analyzeThe Analyze Module records and displays what happened in an imaging session. That is, it does not control any if your imaging, but rather reviews what occurred. Sessions are stored in an analyze folder, a sister folder to the main logging folder. The .analyze files written there can be loaded into the Analyze tab to be viewed. Analyze also can display data from the current imaging session.The Analyze Module records and displays what happened in an imaging session. That is, it does not control any if your imaging, but rather reviews what occurred. Sessions are stored in an analyze folder, a sister folder to the main logging folder. The .analyze files written there can be loaded into the Analyze tab to be viewed. Analyze also can display data from the current imaging session.

There are two main graphs, Timeline and Stats. They are coordinated—they always display the same time interval from the Ekos session, though the x-axis of the Timeline shows seconds elapsed from the start of the log, and Stats shows clock time. The x-axis can be zoomed in and out with the +/- button, mouse wheel, as well as with standard keyboard shortcuts (eg. zoom-in == Ctrl +) The x-axis can be panned with the scroll bar as well as with the left and right arrow keys. You can view your current imaging session, or review old sessions by loading .analyze files using the Input dropdown. Checking Full Width displays all the data, and Latest displays the most recent data (you can control the width by zooming). 


Timeline shows the major Ekos processes, and when they were active. For instance, the Capture line shows when images were taken (green sections) and when imaging was aborted (red sections). Clicking on a green section gives information about that image, and double clicking on one brings up the image taken then in a fitsviewer, if it is available.Timeline shows the major Ekos processes, and when they were active. For instance, the Capture line shows when images were taken (green sections) and when imaging was aborted (red sections). Clicking on a green section gives information about that image, and double clicking on one brings up the image taken then in a fitsviewer, if it is available.

If you have moved your captured images, you can set alternate directory in the input menu to a directory which is the base of part of the original file path.

Clicking on a Focus segment shows focus session information and displays up the position vs HFR measurements from that session. Clicking on a Guider segment shows a drift plot from that session, (if it's guiding) and the session's RMS statistics. Other timelines show status information when clicked. 


A variety of statistics can be displayed on the Stats graph. There are too many for all to be shown in a readable way, so select among them with the checkboxes. A reasonable way to start might be to use rms, snr (using the internal guider with SEP Multistar), and hfr (if you have auto-compute HFR in the FITS options). Experiment with others. The axis shown (0-5) is appropriate only for ra/dec error, drift, rms, pulses, and hfr. These may be y-axis scaled (awkwardly) using the mouse wheel, but the other graphs cannot be scaled. To reset y-axis zooming, right-click on the Stats plot. Clicking on the graph fills in the values of the displayed statistics. This graph is zoomed and panned horizontally in coordination with the timeline.


The observatory module is used to manage the dome and weather-triggered shutdown procedure. It has weather data directly displayed in the module. Along with the configurable thresholds for Warning and Alert states, you can rest easily knowing that KStars can take the appropriate actions to protect your observatory from adverse weather conditions. The observatory module also includes a dedicated weather widget with love plotting for each parameter.



  • Position: Controls the position of the Dome.observatory dome
    • Motion: You can move the Dome in four ways.
      • Absolute: Select the absolute position you want the Dome to move and then click on Move (abs). This will move the Dome to the absolute position you set.
      • Relative: Select the amount of degrees (either positive or negative) you want the Dome to move from the current position and then click on Move (rel). This will move the Dome to the relative position you set.
      • Clockwise (CW): Rotates the Dome Clockwise forever until you click on Abort.
      • Counter Clockwise (CCW): Rotates the Dome Clockwise forever until you click on Abort.
  • Slaving: If enabled, Dome motion will follow telescope motion.
  • Park/Unpark: Park or Unpark the Dome. For advanced control, please use the INDI Control Panel.
  • Abort: Aborts the Dome motion.

Shutterobservatory shutter

  • Open/Close: You can open or close your shutter through the observatory module.

Observatory Status

  • Dome: If selected, the dome needs to be unparked for the observatory status being "READY".observatory status
  • Shutter: If selected, the shutter needs to be open for the observatory status being "READY".
  • Weather: If selected, the weather needs to be OK for the observatory status being "READY".
  • Ready: Observatory status. Select the observatory elements that are relevant for the status:
    • Dome: unparked → ready
    • Shutter: open → ready
    • Weather: OK → ready

Weatherobservatory weather widget

Current data of the weather sensors. Click on the sensor name to display its data over time.

  • auto scale values: Scale the value axis to the current value range.
  • trash canClear sensor data history.
  • Graph: You can see the values of both axes if you hover over the graph. You can zoom in or out using the scroll wheel.


  • Alert: Check this checkbox in order to get an Alert whenever any weather value goes under or above the range set in your weather driver INDI Control Panel.
    • Park Dome: Parks the dome whenever you get an alert.observatory actions
    • Close Shutter: Closes the shutter whenever you get an alert.
    • Status: Shows the status of the alert.
    • Delay (sec): Delays the alert after n amount of seconds.
  • Warning: Check this checkbox in order to get an Warning whenever any weather value is close to going under or above the range set in your weather driver INDI Control Panel.
    • Park Dome: Parks the dome whenever you get a warning.
    • Close Shutter: Closes the shutter whenever you get a warning.
    • Status: Shows the status of the warning.
    • Delay (sec): Delays the warning after n amount of seconds.


ekos astrometry

Ekos Alignment Module enables highly accurate GOTOs to within sub-arcseconds accuracy and can measure and correct polar alignment errors. This is possible thanks to the StellarSolver library. Ekos begins by capturing an image of a starfield, feeding that image to the solver, and getting the central coordinates (RA, DEC) of the image. The solver essentially performs a pattern recognition against a catalog of millions of stars. Once the coordinates are determined, the true pointing of the telescope is known.

Often, there is a discrepancy between where the telescope thinks it is looking at and where it is truly pointing. The magnitude of this discrepancy can range from a few arcminutes to a couple of degrees. Ekos can then correct the discrepancy by either syncing to the new coordinates, or by slewing the mount to the desired target originally requested.

Furthermore, Ekos provides the Polar Alignment Assitant Tool: An easy to use tool for measuring and correcting polar errors. It takes three images any where in the sky (prefreably close to the celestial poles but not required) and then calculates the offset between the mount axis and polar axis.

At a minimum, you need a camera and a mount that supports Slew & Sync commands. Most popular commercial mounts nowadays support such commands.

For the Ekos Alignment Module to work, you have an option of either utilizing the built-in StellarSolver, or remote solver

  • StellarSolver: The default solver in Ekos. StellarSolver supports native plate-solving based on Furthermore, it supports online (internet-based) solving, ASTAP, and local offline solver (Available for macOS & Linux). The built-in solver is fast and supported across all platforms.
  • Remote Solver: The remote solver is an offline solver the resides on a different machine (for example, you can use Astrometry solver on StellarMate). Captured images are solved on the remote machine.

Alignment vs Polar Alignment

It is important to understand the differences between Alignment (or more accurately GOTO Alignment) and Polar Alignment. They are two very different procedures that are designed for different purposes. The following is a summary on what each method is used for.

Goto Alignment
 Polar Alignment
  •  Used to improve the Mount GOTO accuracy by plate-solving images to determine the mount actual pointing position in the sky and then correcting the mount position until it is the target is centered in the camera's Field of View (FOV).
  • Each time an image is plate-solved successfully, a Sync point is appended to the Mount Model. With more points added, the mount GOTO accuracy would improve especially if there are sync points close to the GOTO target.
  • Used to align the mount's Right-Ascension axis with the celestial pole. This is done to improve Tracking Accuracy for long exposure astrophtograohy where the mount is required to compensate for the Earth's rotation by moving the mount at a specific speed in order to the keep the target in the center of the frame at all times. 
  • The offset between the mount's RA axis and polar axis is calculated by taking three separate images while rotating the mount by a fixed degree after each image. After the polar error is measured, the error can be reduced by adjusting the mount's Alt and Azimuth knobs until the Mount Axis coincides with the Polar Axis.

StellarSolver Integrationekos astrometry

StellarSolver is an astrometric plate-solving library that has been integrated into Ekos in order to provide accurate and efficient offline plate solving.

For plate-solving there are several parts in StellarSolver that are important:

Source Extraction

To find the stars in your image in order to solve. In StellarSolver, there are options for 3 different methods:

  • Internal SEP: this requires no external programs, it is the same SEP star extraction algorithm that has existed in KStars for Focus and Guiding for awhile noSource Extractionw. It is essentially a library version of the method below (though there are some differences which is why they give slightly different results). It is entirely internal to the program, so there are no files saved to disk for the extraction which is great for Raspberry Pis etc.
  • External Sextractor: this does require an external program, SExtractor, or the Source Extractor. This is their official standalone program. The drawback is you would need to have sextractor installed and it does save a bunch of files to disk in order to do its operations.
  • BuiltIn Sextractor: This uses whatever method of source extraction the solver uses by default. StellarSolver uses SEP, just like the Internal SEP setting. Local uses its own source extraction method which uses a bunch of external resources including python, netpbm and other packages. And finally, ASTAP has its own internal source extractor which is pretty good.

Note: Either Internal SEP or External Sextractor should be superior to the built-in version of the programs. SExtractor is very good at extracting stars, and that greatly speeds up solving, but it requires tuning up the options to perfect it for your optical train.

The Solver

The program that will be used to do the solving of the sources that were found. In StellarSolver, there are 4 options for that

  • StellarSolver: This option uses an internal library build of It uses no external files like configuration files etc, and saves no files to disk (except 0KB solved and cancel files) which is great forsolving method Raspberry Pis. Since this library is entirely internal, no programs have to be installed beyond KStars itself, so if you are going to use this option, you don't need the package at all. This is going to make a world of difference for Windows users who cannot install unless they do it in a compatibility layer.
  • Local This option uses the good old fashioned local installation many users have used with KStars for years. The only differences in Stellarsolver are that we no longer need the configuration files, we can do parallelization to make it MUCH faster, and we can use Internal SEP or External Sextractor to give it the sources to solve.
  • Local ASTAP: ASTAP was available in KStars previously, but more options have been implemented for using it in StellarSolver as well as giving you the option to use Internal SEP or SExtractor with it. The options for ASTAP are now shared with astrometry so you can just set your options in the profile and it will work fine. ASTAP does NOT support parallelization.
  • Online This option was previously available in KStars as well, but a bunch of work has been done on it to make it work better, to use Internal SEP or Sextractor if you like, to use the options in the profiles, and to provide clearer feedback to the user about what is going on. Technically, online is already using parallelization on their server, so there was no need to implement parallelization for it.

The Options Profiles

Here are the profiles that have been developed:

Profiles mainly for Solving:
1-FastSolving: solve images fast, but it does not do parallel solves.
2-ParallelSolving: It can be faster than FastSolving, but does not work nearly as well as the next 2.
3-ParalleLargeScale: This profile is meant to solve DSLR scale images very fast. It assumes larger image scales to solve faster than the above.
4-ParallelSmallScale: The DEFAULT for solving. This profile is meant to solve telescopic images quickly. Most users should probably use this one.

Profiles mainly for Source Extraction in Focus and Guide
5-AllStars: This profile is meant to detect all the stars in an image.
6-SmallSizedStars: detects smaller stars and ignores bigger stars
7-MidSizedStars: detects medium-sized stars
8-BigSizedStars: detects bigger stars and ignores smaller stars

ANSVR Solver

Users on Windows OS can install ANSVR Local solver and use it as a pseudo online solver that happens to be running a server on their machine. It is not recommended given that StellarSolver is built-in and faster. It is left in the documentation for users who want to try it out.

ANSVR mimics the online server services on your local computer; thus the internet not required for any astrometry queries. From the point of view of Ekos, it is still communicating with an online server.

After installing the ANSVR server and downloading the appropriate index files for your setup, make sure ANSVR server is up and running and then go to Ekos Alignment options where you can simply change the API URL to use the ANSVR server as illustrated below:

astrometry windows ansvr

Do not forget to include the full URL including the HTTP part. In Ekos Align module, you must set the solver type to Online so that it uses the local ANSVR server for all astrometry queries. Then you can use the align module as you would normally do. 

Remember as indicated above that StellarMate already includes Therefore, if you would like to use StellarMate remotely to solve your images, simply change the solver type to Remote and ensure that your equipment profile includes Astrometry driver which can be selected under the Auxiliary dropdown. This is applicable to all operating systems and not just Windows.

Download Index Files

For offline (and remote) solvers, index files are necessary for the solver to work. The complete collection of index files is huge (over 30 GB), but you only need to download what is necessary for your equipment setup. Index files are sorted by the Field-Of-View (FOV) range they cover. There are two methods to fetch the necessary index files: The new download support in Align module, and the old manual way.

Automatic Download

astrometry indexes settings

Automatic download is only available for Ekos users on Linux & macOS. For Windows users, please download ANSVR solver.

To access the download page, click the Options button in the Align module and then select Astrometry Index Files tab. The page displays the current FOV of your current setup and below it a list of available and installed index files. Three icons are used to designate the importance of index files given your current setup as following:

  • Required Required
  • Recommended Recommended
  • Optional Optional 

You must download all the required files, and if you have plenty of hard drive space left, you can also download the recommended indexes. If an index file is installed, the checkmark shall be checked, otherwise check it to download the relevant index file. By default, StellarMate comes pre-installed with index files 4206 to 4219. Due to size restrictions, indexes 4204 and 4205 are not included in the official StellarMate OS image. It is recommended to download them. From Astrometry Index Files tab, click on Index File Location combo and select the first entry below All Sources. Once selected, you should be able to download the necessary index files as illustrated below.

Astrometry Settings

Please only download one file at a time, especially for larger files. Once you installed all the required files, you can begin using the offline solver immediately.

Manual Download

You need to download and install the necessary index files suitable for your telescope+CCD field of view (FOV). You need to install index files covering 100% to 10% of your FOV. For example, if your FOV is 60 arcminutes, you need to install index files covering skymarks from 6 arcminutes (10%) to 60 arcminutes (100%). There are many online tools to calculate FOVs, such as Starizona Field of View Calculator.

Index FilenameFOV (arcminutes)Debian Package
index-4219.fits 1400 - 2000 astrometry-data-4208-4219
index-4218.fits 1000 - 1400
index-4217.fits 680 - 1000
index-4216.fits 480 - 680
index-4215.fits 340 - 480
index-4214.fits 240 - 340
index-4213.fits 170 - 240
index-4212.fits 120 - 170
index-4211.fits 85 - 120
index-4210.fits 60 - 85
index-4209.fits 42 - 60
index-4208.fits 30 - 42
index-4207-*.fits 22 - 30 astrometry-data-4207
index-4206-*.fits 16 - 22 astrometry-data-4206
index-4205-*.fits 11 - 16 astrometry-data-4205
index-4204-*.fits 8 - 11 astrometry-data-4204
index-4203-*.fits 5.6 - 8.0 astrometry-data-4203
index-4202-*.fits 4.0 - 5.6 astrometry-data-4202
index-4201-*.fits 2.8 - 4.0 astrometry-data-4201-1
index-4200-*.fits 2.0 - 2.8 astrometry-data-4200-1

The Debian packages are suitable for any Debian-based distribution (Ubuntu, Mint...etc). If you downloaded the Debian Packages above for your FOV range, you can install them from your favorite package manager, or via the following command:

sudo dpkg -i astrometry-data-*.deb

On the other hand, if you downloaded the FITS index files directly, copy them to /usr/share/astrometry directory.

It is recommended to use a download manager as such DownThemAll! for Firefox to download the Debian packages as browsers' built-in download manager may have problems with download large packages.

How to Use?

Ekos Align Module offers multiple functions to aid you in achieving accurate GOTOs. Start with your mount in home position with the telescope tube looking directly at the celestial pole. For users in Northern Hemisphere, point the telescope as close as possible to Polaris. Initial 2-3 star alignment might be required depending on your mount make:

  • EQMod, Celestron Aux (e.g. Evolution), AstroTrac: No need to perform initial alignment, Ekos alignment module can work with the mount right away after power up given the mount is in its home position.
  • All other Mount drivers: Must intially perform 2-3 star alignment using the handset before you can use the Ekos alignment module.

Ekos Alignment module features the following functions:

  • Optical Train: Select which optical train to use for alignment. Usally, it is the Primary optical train used in Camera module as well. Edit the optical train to ensure that the correct camera and telescope are selected. If using a focal reducer or balow, please specify it in the train configuration.
  • Capture & Solve: Capture an image and determine what region in the sky the telescope is exactly looking at. The astrometry results include the equatorial coordinates (RA & DEC) of the center of the captured image in addition to pixel scale and field rotation. Depending on the Solver Action settings, the results can be used to Sync the mount or Sync and then Slew to the target location. For example, suppose you slewed the mount to Vega then used Capture & Solve. If the actual telescope location is different from Vega, it will be first synced to the solved coordinate and then Ekos shall command the mount to slew to Vega. After slew is complete, the Alignment module will repeat Capture & Solve process again until the error between reported and actual position falls below the accuracy thresholds (30 arcseconds by default).
  • Load & Slew: Load a FITS or JPEG file, solve it, and then slew to it.
  • Polar Alignment Assistant: A simple tool to aid in polar alignment of German Equatorial Mounts.

Warning! Never solve an image at or near the celestial pole (unless Ekos Polar Alignment Assistant Tool is used). Slew at least 20 degrees away from the celetial pole before solving the first image. Solving very close to the poles will make your mount pointing worse so avoid it.

Plate Solve Capture Settingsastrometry settings

Configure plate solving capture settings:

  • Exposure: Exposure duration in seconds
  • Bining: Camera binning (2x2 is by default). Use 2x2 or 4x4 to speed up the process.
  • Gain: For cameras supporting gain, set the desired gain.
  • ISO: For cameras supporting ISO (e.g. DSLRs), set the desired ISO.
  • Dark: Perform dark subtraction if a suitable dark frame is found in the Dark Library.
  • Filter: If a filter wheel is used, then use this filter when capturing align images regardless of filter used in other modules.
  • Solver Mode: Select solver mode (StellarSolver or Remote). Remote solver is only available when connecting to a remote device.

By default, the solver will search all over the sky to determine the coordinates of the captured image. This can take a lot of time; therefore, in order to speed up the solver, you can restrict it to only search within a specified area in the sky designated by the RA, DEC, and Radius options above. Settings

Options for offline and online solvers.

stellarsolver options

Most of the options are sufficient by default. If you have installed in a non-standard location, you can change the paths as necessary.

  • Rotator: Rotator threshold in arc-minutes when using Load & Slew. If the difference between measured position angle and FITS position angle is below this value, the Load & Slew operation is considered successful.
  • Time out: Timeout in seconds to wait for astrometry solver to complete.
  • WCS: World-Coordinate-System is a system for embedding equatorial coordinate information within the image. Therefore, when you view the image, you can hover it and view the coordinate for each pixel. You can also click anywhere in the image and command to the telescope to slew there. It is highly recommeneded to keep this option on.
  • Overlay: Overlay captured images unto the sky map of KStars.
  • Upload JPG: When using online, upload all images are JPEGs to save bandwidth as FITS images can be large.
  • Auto Park: Automatically park the mount after completing Polar Alignment Assistant Tools.

Warning: Turning Auto Park off might lead to inaccurate results.

Solver Options

Ekos selects and updates the optimal options by default to accelerate the performance of the solver. You may opt to change the options that are passed to the solver in case the default options are not sufficient.

Imaging Options

  • Use Scale: Use image scale to speed up astrometry solver. This speeds up the solver greatly as it limits the number of images scales it needs to sift through.
    • Low: The lower end of the imager scale, calculated as a little smaller than the shorter dimension of the image.
    • High: The high end of the imager scale, calculated as a little bigger than the longer dimension of the image.imaging options
    • Units: The units of the imager scale bounds above.
      • dw: degree width
      • aw: arcminute width
      • app: arcsecs per pixel
    • : Update Image Scale Bounds from the currently active camera and telescope combination.
  • Auto Update: Automatically update image scale values when CCD and/or Mount parameters are updated.
  • Down Sample: Downsample the image to shrink its size and speed up the solver.
    • Auto: Automatically determine downsample value based on image size

Position Options

  • Use differential slewing instead of syncing: Do not use Sync when Slew to Target is selected. Use differential slewing to correct for discrepancies. This is useful on some mounts (e.g. Paramount).
  • Use position: Limit the astrometry solver to only search for solutions near the mount coordinates. This can significantly speed up the solving process..
    • RA: The RA of the Estimated Telescope/Image Field Position in hh:mm:ss notationposition options
    • DEC: The DEC of the Estimated Telescope/Image Field Position in dd:mm:ss notation
    • Radius: The Search Radius for the Estimated Telescope/Image Field Position in degrees.
    • : Update coordinates to the current telescope position.
  • Auto Update: Automatically update position coordinates when mount completes slewing.
  • Custom: Additional optional options.

If solving always fail even though the image contains lots of focused stars, then it is likely that either the frame field of view (FOV) and/or mount position is wrong. Turn off Use Scale or Use Position then try solving again. If the solving succeeds then that confirms that either the FOV scale or position are indeed incorrect.

Capture & Solve

Using Ekos Alignment Module, aligning your mount using the controller's 1, 2, or 3 star alignment is not strictly necessary, though for some mounts it is recommended to perform a rough 1 or 2 star alignment before using Ekos alignment module. If you are using EQMod, you can start using Ekos alignment module right away. A typical workflow for GOTO alignment involves the following steps:

  1. Set your mount to its home position (usually the NCP for equatorial mounts)
  2. Select Slew to Target in the Solver Action.
  3. Slew to a nearby bright star.
  4. After slew is complete, click Capture & Solve

If the solver is successful, Ekos will sync and then slew to the star. The results are displayed in the Solution Results tab along with a bullseye diagram that shows the offset the reported telescope coordinates (i.e. where the telescope thinks it is looking at) vs. its actual position in the sky as determined by the solver.

Each time the solver is executed and returns successful results, Ekos can run on the following actions:

  • Sync: Syncs the telescope coordinates to the solution coordinates.
  • Slew to Target: Syncs the telescope coordinates to the solution coordinates and then slew to the target.
  • Nothing: Just solve the image and display the solution coordinates.


Sometimes, the solver would fail to solve an image for various reasons. Here are some tips to get you started in the right direction:

Insufficient stars. Astrometry requires a few clearly visible and defined stars.
  1. Increase Exposure Time.
  2. Increase Gain and/or ISO settings.
  3. Change binning to 2x2 or 4x4
  4. Enable Dark frame subtraction. This helps in reducing the noise in the image.
Change Camera Settings in Ekos Alignment module.  Edit Align presets and change camera settings. 
Unfocused image. Focused star field is necessary for astrometry to work. Focus the camera until you get pin-point stars. Focus camera automatically or manually via Focus module. Focus camera automatically or manually via Focus module. 
Wrong Field of View value. Ekos displays the FOV in arcminutes.
  1. Verify your equipment FOV using online FOV calculator (Imaging Mode).
  2. Ensure the telescope focal length is correct.
  3. If using a reducer/corrector, then you must specify this value in the Optical Train.
  4. FOV depends on camera pixel size in micrometers. While it is very rare for this value to be incorrect, double check the camera pixel size is reported correctly in INDI Control Paneli> → Image Info tab.
Wrong Mount position. Astrometry works when the mount is relatively close to the GOTO target. If it is too far away (more than a couple of degrees) then astrometry may fail.
  1. For handset-controlled mounts, ensure a successful completion of 2-star or 3-star alignment routines before connecting the mount to StellarMate. It's recommended to turn off DST (Daylight Time Savings) as this might interfer with time handling in StellarMate.
  2. For direct-controlled mounts (EQMod, Celestron WiFi..etc), ensure that the mount is powered in its correct home position.
  3. Ensure that the date and time are correct. Incorrect time may lead the mount to a totally different location in the sky.
  4. Ensure geographic location is correct.
  5. While polar alignment is not strictly necessary for accurate GOTO (it mostly affects tracking accuracy). It's recomended to have equatorial mounts polar aligned.
  6. Do the RA/DE coordinates of the telescope make sense? By default, the solver searches within 30 degrees of the current mount location. If the mount is way off in the sky, the solver would fail. If this happens, go back to your parking home position and then slew to a nearby star. If the star is off by more than 30 degrees, then there is something wrong with the mount, time, and location settings so check each of those.
  SM App syncs the device time and location from the phone/tablet GPS automatically upon connection.
Missing astrometry index files By default StellarMate come preinstalled with index files 4206 to 4219, but if your FOV is on the narrower scale, you might need to install more index files.    
Automatic Downsampling
  • Automatic downsampling is turned on by default. It essentially reduces the size of your image before it is fed to the solver. For most users, this option improves solver efficiency. However, it can create issues for others. Go to Astrometry options and turn off automatic downsampling and if that doesn't work, try turning off downsampling completely.


Polar Alignment

Polar Alignment Assitant

When setting up a German Equatorial Mount (GEM) for imaging, a critical aspect of capturing long-exposure images is to ensure a proper polar alignment. A GEM mount has two axis: Right Ascension (RA) axis and Declination (DE) axis. Ideally, the RA axis should be aligned with the celestial sphere polar axis. A mount's job is to track the stars motion around the sky, from the moment they rise at the eastern horizon, all the way up across the median, and westward until they set.

In long exposure imaging, a camera is attached to the telescope where the image sensor captures incoming photons from a particular area in the sky. The incident photons have to strike the same photo-site over and over again if we are to gather clear and crisp image. Of course, actual photons do not behave in this way: optics, atmosphere, seeing quality all scatter and refract photons in one way or another. Furthermore, photons do not arrive uniformly but follow a Poisson distribution. For point-like sources like stars, a point spread function describes how photons are spatially distributed across the pixels. Nevertheless, the overall idea we want to keep the source photons hitting the same pixels. Otherwise, we might end up with an image plagued with various trail artifacts.


Since mounts are not perfect, they cannot perfectly keep track of object as it transits across the sky. This can stem from many factors, one of which is the misalignment of the mount's Right Ascension axis with respect to the celestial pole axis. Polar alignment removes one of the biggest sources of tracking errors in the mount, but other sources of error still play a factor. If properly aligned, some mounts can track an object for a few minutes with only deviation of 1-2 arcsec RMS.

However, unless you have a top of the line mount, then you'd probably want to use an autoguider to keep the same star locked in the same position over time. Despite all of this, if the axis of the mount is not properly aligned with the celestial pole, then even a mechanically-perfect mount would lose tracking with time. Tracking errors are proportional to the magnitude of the misalignment. It is therefore very important for long exposure imaging to get the mount polar aligned to reduce any residual errors as it spans across the sky.

Before starting the process, point the mount as close as possible to the celestial pole. If you are living in the Northern Hemisphere, point it as close as possible to Polaris.

The tool works by capturing and solving three images. After capturing each, the mount rotates by a fixed amount, and another image is captured and solved.

polar align start

After the first capture, you can rotate the mount by a specific amount (default 30 degrees) either West or East. After selecting the magnitude and direction, click Next to continue and the mount will be rotated. Once the rotation is complete you shall be asked to take another capture, unless you have checked Auto Mode. In Automated mode, the rest of the process will continue with the same settings and direction until a total of three images are captured.

Since the mount's true RA/DE are resolved by astrometry, we can construct a unique circle from the three centers found in the astrometry solutions. The circle's center is where the mount rotates about (RA Axis) and ideally, this point should coincide with the celestial pole. However, if there is a misalignment, then Ekos draws a correction vector. This correction vector can be placed anywhere in the image. Next, refresh the camera feed and make corrections to the mount's Altitude and Azimuth knobs until the star is located in the designated cross-hair. To make it easy to make corrections, expand the view by clicking on the Fullscreen button.

polar align manual rotate

If you are away from StellarMate or PC, you can use your Tablet to monitor the camera feed while making corrections. Use the StellarMate's web-based VNC viewer or use any VNC Client on your tablet to access StellarMate. If Ekos is running on your PC, you can use applications like TeamViewer to achieve the same results. The following is a video demonstrating how to utilize the Polar Alignment Assistant tool.


Legacy Polar Alignment Workflow

Using the Polar Alignment mode, Ekos can measure and correct for polar alignment errors. To measure Azimuth error, point your mount to a star close to the meridian. If you live in the northerm hemisphere, you will point the mount toward the southern meridian. Click on Measure Az Error to begin the process. Ekos will try to measure the drift between two images and calculates the error accordingly. You can ask Ekos to correct Azimuth error by clicking on Correct Az Error button. Ekos will slew to a new location and asks you to adjust the mount's azimuth knobs until the star is in the center of the Field of View. You can use the Focus Module's Framing feature to take a look at the image as you make your adjustments.

Similarly, to measure Altitude error, click on the Measure Alt Error button. You need to point your mount either east or west, and set the Altitude Direction combo box accordingly. Ekos will take two images and calculates the error. You can ask Ekos to correct Altitude error by clicking on the Correct Alt Error button. As with Azimuth correction, Ekos will slew to a new location and asks you to adjust the mount's altitude knobs until the star is in the center of the FOV.

After making a correction, it is recommended to measure the Azimuth and Altitude errors again and gauge the difference. You may need to perform the correction more than once to obtain optimal results.

Before starting the Polar Alignment tool, you must complete the GOTO Workflow above for at least one point in the sky. Once your mount is aligned, proceed with the following (assuming you live in the northern hemisphere):

  1. Slew to a bright star (4th magnitude or below) near the southern meridian (Azimuth 180). Make sure Slew to Target is selected. Capture and solve. The star should be exactly centered in your CCD field of view.
  2. Switch mode to Polar Alignment. Click Measure Az Error. It will ask you to slew to a star at the southern meridian which we already done, click continue. Ekos will now perform the error calculation.
  3. If all goes well, the error is displayed in the output boxes. To correct for the error, click Correct Az Error. Ekos will now slew to a different point in the sky, and you will be required to ONLY adjust the mount's azimuth knobs to center the star in the field of view. The most convenient way of monitoring the star field is by going to the Focus module and clicking Start Framing. If the azimuth error is great, the star might not be visible in the CCD field of view, and therefore you have to make blind adjustments (or simply look through the finderscope) until the star enters the CCD FOV.
  4. Begin your azimuth adjustments until the bright star you slewed to initially is as close to center as you can get it
  5. Stop Framing in the Focus module.
  6. Repeat the Measure Az Error to ensure we indeed corrected the error. You might have to run it more than once to ensure the results are valid.
  7. Switch mode to GOTO.
  8. Now slew to a bright star either on the eastern or western horizon, preferably above 20 degrees altitude. It has to be as close as possible to the eastern (90 azimuth) or western (270) cardinal points.
  9. After slew is complete, capture and solve. The star should be dead center in the CCD FOV now.
  10. Switch mode to Polar Alignment
  11. Click Measure Alt Error. It will ask you to slew to a star at either the eastern (Azimuth 90) or western (Azimuth 270) which we already done, click continue. Ekos will now perform the error calculation.
  12. To correct for the error, click Correct Alt Error. Ekos will now slew to a different point in the sky, and you will be required to ONLY adjust the mount's altitude knobs to center the star in the field of view. Start framing as done before in the focus module to help you with the centering.
  13. After centering is complete, stop framing.
  14. Repeat the Measure Alt Error to ensure we indeed corrected the error. You might have to run it more than once to ensure the results are valid.
  15. Polar alignment is now complete!

The mount may slew to a dangerous position and you might risk hitting the tripod and/or other equipment. Carefully monitor the mount's motion. Use at your own risk.

ekos scheduler


Ekos Scheduler is an indispensable arsenal in building your robotic observatory. A Robotic observatory is an observatory composed of several subsystems that are orchestrated together to achieve a set of scientific objectives without direct human intervention. 

It’s recommended to use Ekos Scheduler after you are familiar with using all the Ekos modules manually first. Fine-tune the settings for each module to suit your particular equipment setup.


Ekos Scheduler provides a simple interface to aid the user in setting the conditions and constraints required for an observation job. Each observation job is composed of the following:

  • Target name and coordinates: Select target from the Find Dialog or Add it from Observation Planner. You can also enter a custom name.
  • Optional FITS file: If a FITS file is specified, the astrometry solver shall solve the file and use the central RA/DEC as the target coordinates.
  • Sequence File: The sequence file is constructed in the Ekos Capture Module. It contains the number of images to capture, filters, temperature settings, prefixes, download directory..etc.
  • Priority: Set job priority in the range of 1 to 20 where 1 designates the highest priority and 20 the lowest priority. Priority is applied in calculating the weight used to select the next target to image. (Only enabled in Classic algorithm)
  • Profile: Select which equipment profile to utilize when starting Ekos. If Ekos & INDI are already started and online, this selection is ignored.
  • Steps: Each job goes through a sequence of discrete steps. Each step or stage can be toggled on or off as desired:
      1. Track: Mount is commanded to slew to target.
      2. Focus: Camera autofocus (if applicable) is started.
      3. Align: Plate-solving is performed to ensure the correct location, framing and orientation of the target is met. If a FITS file is specified in General Settings, then this file is first plate-solved and then mount is commanded to to slew to target solution coordinates. This is followed by another plate-solving process to ensure we are within tolerance at the target solution coordinates. If the position angle of the FITS image is different from the current camera orientation, the camera orientation can be automatically adjusted if a mechanized rotator is detected. Otherwise, a manual camera rotation is required until the image position angle is satisfied.
      4. Guide: Using a guide camera, the mount tracking is locked to a guide star to enable long-exposure astrophotography
  • Startup Conditions: Conditions that must be met before the observation job is started. Currently, the user may select to start as soon as possible Now, or when the target is near or past culmination, or at a specific time.
  • Constraints: Constraints are conditions that must be met at all times during the observation job execution process. These include minimum target altitude, minimum moon separation, twilight observeration, and weather monitoring.
  • Completion Conditions: Conditions that trigger completion of the observation job. The default selection is to simply mark the observation job as complete once the sequence process is complete. Additional conditions enable the user to repeat the sequence process indefinitely or up until a specific time.

You must select the Target and Sequence before you can add a job to the Scheduler. When the scheduler starts, it evaluates all jobs in accord to the conditions and constraints specified and attempts to select the best job to execute. Selection of the job depends on a simple heuristic algorithm that scores each job given the conditions and constraints, each of which is weighted accordingly. If two targets have identical conditions and constraints, usually the higher priority target followed by higher altitude target is selected for execution. If no candidates are available at the current time, the scheduler goes into sleep mode and wakes up when the next job is ready for execution.

scheduler planner

The description above only tackles the Data Acquisition stage of the observatory workflow. The overall procedure typically utilized in an observatory can be summarized in three primary stages:

  1. Startup
  2. Data Acquisition (including preprocessing and storage)
  3. Shutdown

Startup Procedure

Startup procedure is unique to each observatory but may include:

  • Turning on power to equipment
  • Running safety/sanity checks
  • Checking weather conditions
  • Turning off light
  • Fan/Light control
  • Unparkig dome
  • Unparking mount
  • ..etc

Ekos Scheduler only initiates the startup procedure once the startup time for the first observation job is close (default lead time is 5 minutes before startup time). Once the startup procedure is completed successfully, the scheduler picks the observation job target and starts the sequence process. If a startup script is specified, it shall be executed first.

Data Aquisition

Depending the on the user selection, the typical workflow proceeds as following:

  • Slew mount to target. If a FITS file was specified, it first solves the files and slew to the file coordinates.
  • Auto-focus target. The autofocus process automatically selects the best star in the frame and runs the autofocus algorithm against it.
  • Perform plate solving, sync mount, and slew to target coordinates.
  • Perform post-alignment focusing since the frame might have moved during the plate solving process.
  • Perform calibration and start auto-guiding: The calibration process automatically selects the best guide star, performs calibration, and starts the autoguide process.
  • Load the sequence file in the Capture module and start the imaging process.


Once the observation job is completed successfully, the scheduler selects the next target. If the next target scheduled time is not due yet, the mount is parked until the target is ready. Furthermore, if the next scheduled target is not due for a user-configurable time limit, the scheduler performs a preemptive shutdown to preserve resources and performs the startup procedure again when the target is due.

If an unrecoverable error occurs, the observatory initiates shutdown procedure. If there is a shutdown script, it will be executed last.

The following video demonstrates an earilar version of the scheduler, but the basic principles still apply today:


The Greedy Scheduler

Greedy Scheduler will allow you to choose a new scheme for scheduling jobs. (In the nightly release) there should now be a scheduling algorithm choice. If you set it to "Classic" (the default), nothing has changed. If you set it to "Greedy" you will see the changes described below.  Note: these changes concern scheduling--deciding which jobs run and when. They do not affect the job management aspects of the scheduler which remain unchanged.

In both the Classic and Greedy schedulers, jobs are listed as "earlier on the job list means higher priority". With the Classic scheduler, priority** is of the highest importance. It will not schedule a lower priority job until the higher priority job is done, even if that job takes several nights, and even if the higher-priority job cannot run at the current time, e.g. due to altitude/terrain/etc.  In contrast to this, the Greedy scheduler attempts to keep Ekos busy as much as possible. Although it gives priority to earlier-listed-jobs, it will run later-listed ones if the earlier one can't run. Of course, the lower priority job will get preempted when the high-priority job can finally start to run.

**In this discussion, "lower priority" means "further down on the job list". and similarly, higher priority is higher/earlier on the job list. We will be phasing out the priority number that can be assigned to jobs on the Classic scheduler.

If the scheduler is started with only one job, there is no difference between Classic and Greedy scheduling. However, if you have more than one job, depending on your setup, there is a good chance that the Greedy scheduler will schedule more imaging time than Classic.

Here's a recommended way to try this out. Let's assume you have a main target for which you want to collect as many images as possible. Set that target up as first on the scheduler list, have it start ASAP and set its completion condition as "Repeat Until Terminated". It should be scheduled to image whenever possible (even across multiple nights) until you turn off the scheduler or Ekos. Add several other targets as well, ones that you might also be interested in, and that can be imaged in other parts of the night. Make sure those are listed below the primary target on the jobs list. Set those the same way (ASAP/RepeatUntilTerminated). They will be scheduled to run whenever the primary target can't be imaged.  Of course, make sure the twilight restriction is set for all your targets. Altitude and terrain restrictions are important as well--if Ekos doesn't know that there's a tree or house blocking your target, it can't be smart about scheduling it.

Since jobs will be preempted/restarted more often with Greedy than with Classic, the "Remember Job Progress" option is now more important. Can find this setting in the KStars Setting Menu --> Ekos --> Scheduler --> "Remember job progress".  This option only works if you are storing images on the same machine where the scheduler is running. Should enable "Remember Job Progress" with this scheduler to get the most benefit, assuming your capture sequences use multiple/different filters. If your capture sequences are just used with one type of filter/or OSC then it probably doesn't matter. (RememberJobProgress has also be updated a bit, and should now do a better job of picking up where the last attempt finished.)

Here is a screenshot of the scheduler running with this new scheme. Note that there are 4 jobs, and they are listed in order of precedence. See the next start times for each of the jobs on the scheduler table, and the highlighted (4th) job is the one currently running. A schedule for the next 48 hours is also printed in the log window at the bottom.


The scheduler is (minimally) integrated with Analyze. Here's a screenshot of the Analyze timeline for the 3 days. (Note some timelines didn't display well because of screen resolution.)  The top line is the new scheduler timeline in Analyze. The different colors correspond to different jobs that were run, each one keeping its same color on different stars (yes, red is an unfortunate choice of colors and I've already submitted code that changes the color scheme for that line). Different jobs can be seen ran as expected each night.


Weather Monitoring

Another critical feature of any remotely operated robotic observatory is weather monitoring. For weather updates, Ekos relies on the selected INDI weather driver to continuously monitor the weather conditions. For simplicity sake, the weather conditions can be summed in three states:

  1. Ok: Weather conditions are clear and optimal for imaging.
  2. Warning: Weather conditions are not clear, seeing is subpar, or partially obstructed and not suitable for imaging. Any further imaging process is suspended until weather improves. Warning weather status does not pose any danger to the observatory equipment so the observatory is kept operational. The exact behavior to take under Warninig status can be configured.
  3. Alert: Weather conditions are detrimental to the observatory safety and shutdown must be initiated as soon as possible.

Aborted Job Management

Define what should happen when a job steps into an error or aborts:

  • Don't re-schedule (None): Don't restart the job in case of an error or an abort.
  • Re-schedule after all terminated (Queue): If a job gets aborted, the scheduler will only re-schedule it if when all jobs are finished or aborted. If this is the case, the scheduler re-schedules all aborted jobs and sleeps for the given delay.
  • Re-schedule immediately (Immediate): As soon as a job gets aborted, the scheduler will re-schedule it and waits the given delay.

If the option for re-scheduling errors is selected, errors are handled like aborts. Otherwise, jobs that step into an error are never re-scheduled.

Startup & Shutdown Scripts

Due to the uniqueness of each observatory, Ekos enables the user to select startup and shutdown scripts. The scripts takes care of any necessary procedures that must take place on startup and shutdown stages. On startup, Ekos executes the startup scripts and only proceeds to the remainder of the startup procedure (unpark dome/unpark mount) if the script completes successfully. Conversely, the shutdown procedure begins with parking the mount & dome before executing the shutdown script as the final procedure.

Startup and shutdown scripts can be written any language that can be executed on the local machine. It must return 0 to report success, any other exist value is considered an error indicator. The script's standard output is also directed to Ekos logger window. The following is as sample demo startup script in Python:

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import os
import time
import sys

print "Turning on observatory equipment..."


print "Checking safety switches..."


print "All systems are GO"


The startup and shutdown scripts must be executable in order for Ekos to invoke them (e.g. use chmod +x to mark the script as executable). Ekos Scheduler enables truly simple robotic operation without the need of any human intervention in any step of the process. Without human presence, it becomes increasingly critical to gracefully recover from failures in any stage of the observation run. Using KDE notifications, the user can configure audible alarms and email notifications for the various events in the scheduler.

Verifying Target Location

Due to a variety of factors, the captured target image might get shifted during the imaging process. Such factors might include:

  • Mount tracking issues.
  • Guiding issues.
  • External factors such as wind or vibrations.

To ensure the target stays centered, configure the scheduler to recheck the image position every few frames. If the captured image position has veered off the original target more than a configure threshold, then the scheduler would immediately abort the imaging and guiding processes, and perform a re-alignment to bring the mount back to the original target. Once this is successfully completed, it would resume the guiding and capturing workflows. You can configure these settings in Settings -> Configure KStars -> Ekos

recheck image

Manual Target Selection

When selecting a target usign the Ekos Find Tool, the objects equatorial coordinates (J2000) are automatically filled in the RA/DE fields. You can also define your own custom target. Simply type in your target name in the target field and then manually enter the desired J2000 coordinates in the respective fields.

KStars provides a conventient method to Copy Coordinates. Simply right-click on the desired object or point in the sky where you want to image, and click copy coordinates. You can paste the coordinates in any text editor and then copy back the J2000 coordinates in the scheduler RA and DE fields as shown below.

copy coordinates

Mosaic Planner

mosaic planner

Hubble-like super wide field images of galaxies and nebulae are truly awe inspiring, and while it takes great skills to obtain such images and process them; many notable names in the field of astrophotography employ gear that is not vastly different from yours or mine. I emphasize vastly because some do indeed have impressive equipment and dedicated observatories worth tens of the thousands of dollars. Nevertheless, many amateurs can obtain stellar wide-field images by combining smaller images into a single grand mosaic.

We are often limited by our camera+telescope Field of View (FOV). By increasing FOV by means of a focal reducer or a shorter tube, we gain a larger sky coverage at the expense of spatial resolution. At the same time, many attractive wide-field targets span multiple FOVs across the sky. Without any changes to your astrophotography gear, it is possible to create a super mosaic image stitched together from several smaller images. There are two major steps to accomplish a super mosaic image:

  1. Capture multiple images spanning the target with some overlap between images. The overlap is necessary to enable the processing software from aligning and joining the sub-images.
  2. Process the images and stitch them into a super mosaic image.

The 2nd step is handled by image processing applications such as PixInsight, among others, and will not be the topic of discussion here. The first step can be accomplished in Ekos Scheduler where it creates a mosaic suitable for your equipment and in accordance to the desired field of view. Not only Ekos creates the mosaic panels for your target, but it also constructs the corresponding observatory jobs required to capture all the images. This greatly facilitates the logistics of capturing many images with different filters and calibration frames across a wide area of the sky.

The Mosaic Planner in the Ekos Scheduler will create multiple Scheduler jobs based on a central target. To toggle the planner, click on the Mosaic Planner button in Ekos Scheduler or KStars INDI toolbar as illustrated in the screenshot. The planner draws the Mosaic Panel directly unto the sky map. It is recommended to enable HiPS overlay for the best experience. The planner is composed of four stages:

  1. Confirm Equipment: Ekos attempts to load equipment settings from INDI. If unsuccessful, you need to enter your equipment settings including your telescope focal length in addition to camera's width, height, and pixel dimensions. The settings are saved for future sessions.

confirm grip

  1. Select Grid: Select the mosaic panel dimension and overlap percentage. The Mosaic Panel is updated accordingly on the sky map. Adjust the Position Angle to match the desired mosaic orientation in the sky. If the Position Angle is different from your camera's usual orientation, you may need to rotate the camera either manually or via a mechanized rotator when the scheduler jobs are executed. Tile transparency is automatically calculated by default but may be turned off and adjusted manually. To compute the mosaic field from the number of tiles, click the Cover FOV button. The mosaic panel can be centered in the sky map by clicking on the Recenter button.

select grid

A large overlap will make frame stitching easier during post-processing, but it requires more panes to cover the desired extent. However, if you already know the minimal amount of sub-frames your rejection algorithm will use during post-processing, you may want to increase the overlap to attain that amount on the areas covered by multiple panes. For instance, a 4x4 mosaic grid with 75% overlap has 16 sub-frames covering the central intersection, which is enough for Winsorized Sigma rejection. Although the resulting stack does not have the same height on all parts of the final frame, this method gives you control on signal-to-noise ratio and allows you to provide context to your target while exposing a relatively low number of captures.

The large number drawn in the corner of each grid pane represents the order in which panes will be captured. The default S-shaped choice (west-east then alternating high-low/low-high moves), ensures minimal movement of the mount during observation. Uncheck Minimum mount move to revert to west-east/high-low movement only. The coordinates of each pane are rendered in their center as degrees, minutes and seconds. Finally, the angle each pane rotates from the center of the mosaic is displayed at the bottom. If your field of view is large, or if your mosaic is located close to a celestial pole, you may observe that rendered panes start rotating visibly due their horizontal position or high declination. Use the overlap to ensure panes cover the desired frame extents properly.

 mosaic grid
  1. Adjust Grid: Adjust Grid center by manually entering the J2000 center or by dragging the center of the mosaic on the sky map.

adjust grid

  1. Create Jobs: The final step is to select the sequence file and directory to store the images. Target field is automatically filled but may be changed as desired. Select the steps each scheduler job should execute in sequence (Track -> Focus -> Align -> Guide -> Capture), and adjust the frequency of automatic alignment and focus routines that must be executed during the mosaic operation. For example, if Align Every is set to 2 Scheduler Jobs, then the first job will run the astrometry alignment, while the second job will skip it. When the third job is executed, alignment is performed again and so forth

create scheduler jobs

Click Create Jobs to generate mosaic scheduler jobs and add them to the schedule queue.


ekos guide


Ekos Guide Module enables autoguiding capability using either the powerful built-in guider, or at your option, external guiding via PHD2 or ln_guider. Using the internal guiding, guider CCD frames are captured and sent to Ekos for analysis. Depending on the deviations of the guide star from its lock position, guiding pulses corrections are sent to your mount Via any device that supports ST4 ports. Alternatively, you may send the corrections to your mount directly, if supported by the mount driver. Most of the GUI options in the Guide Module are well documented so just hover your mouse over an item and a tooltip will popup with helpful information.


Each module has it's own train. You can use a specific train for Guide module. Click here to know more about Optical trains.

To perform guiding, you need to select a Guider CCD in Ekos Profile Setup. The telescope aperture and focal length must be set in the telescope driver. If the Guider CCD is attached to a separate Guide Scope, you must also set the Guide Scope's Focal Length and Aperture. You can set these values under the Options tab of the telescope driver or from the Mount module. Autoguiding is a two-step process: Calibration & Guiding.

During the two processes, you must set the following:

  • Exposure: CCD Exposure in seconds.
  • Binning: CCD Binning.
  • Box: Size of box enclosing the guide star. Select a suitable size that is neither too large or too small for the selected star.
  • Effects: Specify filter to be applied to the image to enhance it.

Main Module Controls

Most of the main module controls are briefly explained in this section.


  • Capture: Takes one capture
  • Guide: Starts the guiding process
  • Stop: Stops the guiding process
  • Loop: Starts taking frames every n seconds (n = exposure value)
  • Subframe: Subframe the image around the guide star. Or for PHD2, receive the Guide Star Image instead of the full image frame. For the Internal Guider, before checking this option, you must first capture an image and select a guide star. Uncheck it to take a full frame again.
  • Auto Star: AutomaticControl
    Capture: Takes one capture
    Guide: Starts the guidally select the calibration star.
  • Dark: Subtract dark frame. If no dark frame is available, a new dark frame shall be captured and saved for future use.
  • Show in FITS Viewer  : Shows frame in FITS Viewer
  • Clear calibration data  : Clears all the calibration data for the guiding process.
  • Manual Dither  : Allows manual dithering.
  • Exp: Exposure time in seconds.
  • Bin: Guide camera binning. It is recommended to set binning to 2x2 or higher.
  • Box: Guide star tracking box size. Box size must be set in accordance to the selected star size.
  • Effects: Apply filter to image after capture to enhance it.
  • Directions: Shows the values of RA and DEC.
    • RA: Guide Right Ascention Axis
        • +: East Direction Guiding
        • -: West Direction Guiding
    • DEC: Guide Declination Axis
      • +: North Direction Guiding
      • -: South Direction Guiding
  • Connect: Connect to external guiding application.
  • Disconnect: Disconnect from external guiding application.

Guide Info

  • Focal length: Guide camera focal length. Unit is in millimeters (mm)
  • Aperture: Guide camera aperture. Unit is in millimeters (mm)
  • F/D: Focal ratio
  • FOV: Field of view (arcmin)
  • Guiding Delta ": Immediate Guiding RA deviation in arcseconds and Immediate Guiding DEC deviation in arcseconds respectively.
  • Pulse Length (ms): Generated RA pulse and Generated DEC pulse respectively.
  • RA RMS": RA Guiding RMS error.
  • DE RMS": DEC Guiding RMS error.
  • Total RMS": Total Guiding RMS error.
  • Guide SNR: Guide Signal-to-noise ratio.

Dark Frames

Dark frames are immensly helpful in reducing noises in your guide frames. It is highly recommended to take dark frames before you begin and calibration or guiding procedure. To take a dark frame, check the Dark checkbox and then click Capture. For the first time this is performed, Ekos will ask you about your camera shutter. If your camera does not have a shutter, then Ekos will warn you anytime you take a dark frame to cover your camera/telescope before proceeding with the capture. On the other hand, if the camera already includes a shutter, then Ekos will directly proceeds with taking the dark frame. All dark frames are automatically saved to Ekos Dark Frame Library. By default, the Dark Library keeps reusing dark frames for 30 days after which it will capture new dark frames. This value is configurable and can be adjusted in Ekos settings in the KStars settings dialog.

dark library

It is recommended to take dark frames covering several binning and exposure values so that they may be reused transparently by Ekos whenever needed.


guide calibration settingsIn the calibration phase, you need to capture an image, select a guide star, and click Guide to begin the calibration process. If calibration was already completed successfully before, then the autoguiding process shall begin immediately, otherwise it would start the calibration process. If Auto Star is checked, then you are only required to click capture and Ekos will automatically select the best fit guide star in the image and continues the calibration process automatically. If Auto Calibration is disabled, Ekos will try to automatically highlight the best guide star in the field. You need to confirm or change the selection before you can start the calibration process. The calibration options are:

  • Pulse: The duration of pulses in milliseconds to be sent to the mount. This value should be large enough to cause a noticable movement in the guide star. If you increase the value and you do not notice any motion of the guide star, then this suggests possible mount issues such as jamming or connection issues via the ST4 cable.
  • Two axis: Check if you want the calibration process calibration in both RA & DEC. If unchecked, the calibration is only performed in RA.
  • Auto Star: If checked, Ekos will attempt to select the best guide star in the frame and begins the calibration process automatically.

The reticle position is the guide star position selected by you (or by the auto selection) in the captured guider image. You should select a star that is not close to the edge. If the image is not clear, you may select different Effects to enhance it.

Ekos begins the calibration process by sending pulses to move the mount in RA and DEC. If the calibration process fails due to short drift, try increasing the pulse duration. To clear calibration, click the trash-bin icon next to Guide button.

Calibration can fail for a variety of reasons. To improve chances of success, try the tips below.

  • Better Polar Alignment: This is critical to the success of any astrophotography session. Perform a quick polar alignment with a polar scope (if available) or by using Ekos Polar Alignment procedure in the Align module.
  • Set binning to 2x2: Binning improves SNR and is often very important to the success of the calibration and guiding procedures.
  • Prefer use ST4 cable between guide-camera and mount over using mount pulse commands.
  • Select different filter (e.g. High contrast) and see if that makes a difference to bring down the noise.
  • Smaller Square Size.
  • Take dark frames to reduce noise.
  • Play with DEC Proportional Gain or disable DEC control completely and see the difference.
  • Leave algorithm to default value (Smart)


guide guide settingsOnce the calibration process is completed successfully, the guiding shall beging automatically hereafter. The guiding performance is displayed in the Drift Graphics region where Green reflects deviations in RA and Blue deviations in DEC. The colors of the RA/DE lines can be changed in KStars color scheme in KStars settings dialog. The vertical axis denotes the deviation in arcsecs from the guide star central position and the horizontal axis denotes time. You can hover over the line to get the exact deviation at this particular point in time. Furthermore, you can also zoom and drag/pan the graph to inspect a specific region of the graph.

Ekos can utilize multiple algorithms to determine the center of mass of the guide star. By default, the smart algorithm is suited best for most situation. The fast algorithm is based on HFR calculations. You can try switching guiding algorithms if Ekos cannot keep of the guide star within the guiding square properly.

The info region displays information on the telescope & FOV, in addition to the deviations from the guide star along with the correction pulses sent to the mount. The RMS value for each axis is displayed along with the total RMS value in arcsecs. The internal guider employs PID controller to correct the mount tracking. Currently, the only the propotional and integral gains are utilized within the algorithm, so adjusting it should affect the length of the generated pulses sent to the mount in milliseconds.

To enable automatic dithering between frames, make sure to check the Dither checkbox. By default, Ekos should dither (i.e. move) the guiding box after each frame captured in Ekos Capture Module. The motion duration and direction are randomized. Ekos will estimate the RA and DEC pulses necessary to move to the randomly generated position, and issue those pulses. Since the guiding performance can oscillate immediately after dithering, you can set the appropriate Settle duration to wait after dither is complete before resuming the capture process. In rare cases where the dithering process can get stuck in an endless loop, set the appropriate Timeout to abort the process. But even if dithering fails, you can select whether this failure should terminate the autoguiding process or not. Toggle Dither Failure Aborts Autoguide to select the desired behavior.

Note: Dithering will not obey the guider's axis and direction restrictions. For instance, if one chooses to only guide in RA, dithering will occur in both RA and DEC.

Non-guide dithering is also supported. This is useful when no guide camera is available or when performing short exposures. In this case, the mount can be commanded to dither in a random direction for up to the pulse specified in the Non-Guide Dither Pulse option.

Ekos supports multiple guiding methods: Internal, PHD2, and LinGuider. You need to select the desired guider in your Ekos equipment profile:

  • Internal Guider: Use Ekos internal guider. This is the default and recommened option.
  • PHD2: Use PHD2 as the external guider. If selected, specify the host and port of the PHD2. Leave to default values if Ekos and PHD2 are running on the same machine.
  • LinGuider: Use LinGuider as the external guider. If selected, specify the host and port of the LinGuider. Leave to default values if Ekos and LinGuider are running on the same machine.

ekos profile guider select


GPG RA Guider

guide guide settings GPGEkos also supports GPG RA Guider, but this is for RA only--that is, guiding for DEC still happens, but using the existing guiding algorithms. This guider can be enabled by going to the Guide Module, clicking on Options (bottom-right) and then clicking on the GPG RA Guider tab and then checking the Enable GPG checkbox. This guider is based on the work in this PhD thesis and is the same as the well-regarded PHD2 guide algorithm known as Predictive PEC. It estimates the periodic error in the guiding system, and tries to fix it before it happens. This system should perform about the same as the standard guider for the first period or two of your mount's periodic error, then improve. When using this system, it's best to set in advance what your mount's worm-gear period is. For example, the Orion Atlas pro is about 480s. You enable this in the Guide options menu, in the GPG RA tab, and then checking "Enable GPG". There are other parameters you can change, but as indicated earlier, the main one to think about is "Major Period".

It can be used with all Guide star-detection algorithms but has been tested most and is recommended with SEP MultiStar. It combines a reactive correction whose aggressiveness is controlled with Control Gain and Minimum Move, with a predictive correction controlled by Prediction Gain. Again, The most important parameter is Major Period. If you can determine it for your mount, it's much
better to set it yourself and uncheck Estimate Period. 

Control Theory

PID guider. Stands for Proportional, Integral, Derivative control.
- Proportional means make corrections based on the error (e.g. you're off by 1 pixel in one direction, put the mount a certain amount in the other direction, and that amount is "control" times the error).
- Integral means look at the recent history of error (e.g. the average error in the past N samples) and make adjustments based on that. KStars defaults to not using that (e.g. the integral gain is 0).
- Derivative isn't implemented in KStars. (It looks at the rate that the system is approaching the target, preventing an overshoot)

If you're using GPG, the above 2 (Proportional & Integral) aren't used for RA, but rather the GPG settings.
Whether or not you're using GPG, DEC is controlled by Proportional and Integral.


  • Enable GPG: Toggles GPG RA Guiding.
  • Major Period: The length in seconds of the mount's major period that's being corrected. (look it up for your mount, and then uncheck estimate period, or alternatively if you're adventurous, run it with estimate period checked for an hour or two, and assuming you like the RA guiding during the last half of the interval, keep the period value it found and uncheck estimate period)
  • Estimate Period: If checked, the GPG estimates the mount's major period. Otherwise, it uses the entry above.
  • Prediction Gain: The fraction of its prediction the GPG uses to move the mount. Similar to Control Gain, but instead of error, now it has started making predictions of how to fix the error (based on the error and based on its periodic error estimate).
  • Control Gain: The fraction of the guide-star drift that the GPG uses to move the mount. The GPG guider at the start uses a simple control mechanism (the pulse tries to correct the error). Control gain of 0.5 means "try to fix half of the error". Setting it 1.0 would likely result in an overcorrected system with poor guiding, so 0.5 is pretty normal.
  • Minimum Move: The min-move parameter the GPG uses to move the mount when it uses its backoff proportional guider. (don't react to errors less that XXX--but really min move is in units of pulse ms, so don't put out a shorter correction pulse than XXX) and Max (don't put out a pulse greater than XXX.)

You can make the GPG guiding less aggressive by reducing control gain. If you want the guiding process to be less aggressive, make the guide exposure pretty long (e.g. 3 or 4 or 5s), reduce the control gain, reduce the prediction gain, and increase the min move. If you suspect that you don't have much periodic error you should consider NOT using GPG.

If you have no idea what to set Control and Prediction gains, keep them around their defaults (in the  0.5 area).

Expert Settings

  • Long-range Length Scale: Length scale of the long range kernel.
  • Long-range Variance: Long-range kernel signal variance
  • Periodic Length Scale: Periodic Kernel length scale
  • Periodic Variance: Periodic kernel signal variance
  • Short-range Length Scale: Length scale of the short-range kernel
  • Short-range Variance: Short-range kernel signal variance
  • Approximation Points: Number of points used in the Gaussian Process approximation
  • Num Periods for Inference: The min number of periods that must be sampled before prediction is fully used. Before that, it is mixed with the control/proportional guider.
  • Num Periods for Period Estimate: The min number of periods that must be sampled before GPG fully estimates the period.

Guiding Direction Control

You can fine tune the guiding performance in the Control Section. The autoguide process works like a PID controller when sending correction commands to the mount. You can alter the Proportional and Integral gains to improve the guiding performance if necessary. By default, guiding corrective pulses are sent to both mount axis in all directions: positive and negative. You can fine-tune control by selecting which axis shall receive corrective guiding pulses and within each axis, you can indicate which direction (Positive) + or Negative (-) recieves the guiding pulses. For example, for Declination axis, the + direction is North and - is South.

Guiding Rate

Each mount has a particular guiding rate in (x15"/sec) and usually ranges from 0.1x, to 1.0x with 0.5x being a common value used by many mounts. The default guiding rate is 0.5x sidereal, which is equivalent to a proportional gain of 133.33. Therefore, set the guiding rate value to whatever value used by your mount, and Ekos shall display the recommended propotional gain value that you may set in the propotationl gain field under the Control Parameters. Setting this value does not change your mount guiding rate! You must change your mount guiding rate either via the INDI driver, if supported, or via the hand controller.

Drift Graphics

guide drift settingsThe drift graphics is a very useful tool to monitor the guiding performance. It is a 2D plot of guiding deviations and corrections. By default, only the guiding deviations in RA and DE are displayed. The horizontal axis is the time in seconds since the autoguiding process was started while the vertical axis plots the guiding drift/deviation in arcsecs for each axis. Guiding corrections (pulses) can also be plotted in the same graph and you can enable them by checking the Corr checkbox below each Axis. The corrections are plotted as shaded areas in the background with the same color as that of the axis.

You can pan and zoom the plot, and when hovering the mouse over the graph, a tooltip is displayed containing information about this specific point in time. It contains the guiding drift and any corrections made, in addition to the local time this even was recorded. A vertical slider to the right of the image can be used to adjust the height of the secondary Y-axis for pulses corrections.

The Trace horizontal slider at the bottom  can be used to scroll through the guide history. Alternatively, you can click the Max checkbox to lock the graph onto the latest point so that the drift graphics autoscrolls. The buttons to the right of the slider are used for autoscaling the graphs, exporting the guide data to a CSV file, clearing all the guide data, and for scaling the target in the Drift Plot. Furthermore, the guide graph includes a label to indicate when a dither occurred so the user knows guiding was not bad at those points.

The colors of each axis can be customized in KStars Settings color scheme.

Drift Plot

A bulls-eye scatter plot can be used to gauge the accuracy of the overall guiding performance. It is composed of three concentric rings of varying radiuses with the central green ring having a default radius of 2 arcsecs. The last RMS value is plotted as add circle with its color reflecting which concentric ring it falls within. You can change the radius of the inner most green circle by adjusting the drift plot accuracy.

Calibration Plot

The Calibration Plot shows the mount positions recorded during internal-guider calibration.
Basically, if things are going well, it should display dots in two lines which are at right angles to each other--one when the calibration pushes the mount back and forth along the RA direction, and then when it does the same for the DEC direction. Not a ton of info, but can be useful to see. If the two lines are at a 30-degree angle, something's not going well with your calibration! Here's a picture of it in action using the simulator.

guide calibration plot

The colored dots (same color scheme as the internal guider) shows the RA and DEC samples on their way out, and the small white and yellow circles show their return paths.

Manual Dither

Screenshot 20220804 083730

After guiding is started, it is possible to adjust the star lock position by clicking the Manual Dither button. The dialog provides two options:

  1. Magnitude: Specify the magnitude of the required manual dither in Pixels. This would move the lock position in a random direction by the specified magnitude.
  2. Coordinates: Specify the exact X,Y coordinates where the lock position should end up at. If the desired lock position is far away (> 3 pixels), it is recommend to move there is small steps. The initial coordinates position are that of the currently locked star.

For Spectroscopy applications, use the Coordinates option to adjust the star so that the target star light falls onto the reflective slit of the spectrograph

Guiding while Cloudy

It is possible to Guide in Ekos while it is partly cloudy. When the camera passes through a layer of clouds, guiding would be aborted followed shortly by the capture sequence. KStars developer Wolfgang Ressenberger suggested a few recommendations when guiding on partly cloudy night:

It does not matter how clouded the sky is as long as the small fraction of the sky you are capturing is clear. So the best approximation that capturing does not make sense is when guiding runs into problems with the guiding star. If there are clouds that are so heavy that guiding get's into trouble, the captured frame is worthless.


If a guiding problem is detected, the best reaction is to immediately abort capturing. You can control this with the following parameters:

  1. Guiding options | Guide | Lost star timeout
    If the guiding star is lost for this period of time, guiding aborts and subsequently capturing aborts. A typical value is 20 seconds.
  2. Capture | Guide Limits | Abort if Guiding DeviationIt might happen that the guide star re-appears, but your scope is already to far off so that continuing would create elongated stars


If you are using the Capture module standalone without the Scheduler, capturing will recover as soon as the guiding deviation is below the configured value. If this is unchecked, capturing will remain aborted.A more robust way for recovery is using the Scheduler. Its main feature is the "Aborted Job Management" that gives you the opportunity to try to restart capturing. There are two options that should be used, depending on the expected scenario:

  1. Aborted Job Management | Immediate
    This is the option that I prefer. If a job aborts due to guiding problems and restarting guiding fails for 5 times, the Scheduler sets the job state to ABORTED and will retry to start it after the configured amount of time. This will happen as long as the constraints of the job remain valid.
  2. Aborted Job Management | Queue
    Similar to 1., but the Scheduler will jump to the next scheduled job and tries to start this one. This variant makes sense if you expect that the clouds remain in a certain part of the sky and starting the other job increases the chances to find some clear sky. From my experience, that does not happen very often and it's better to stay a a certain target.

PHD2 Support

You can opt to select external PHD2 application to perform guiding instead of the built-in guider.

ekos guide phd2

If PHD2 is selected, the Connect and Disconnect buttons are enabled to allow you to establish connection with the PHD2 server. You can control PHD2 exposure and DEC guide settings. When clicking Guide, PHD2 should perform all the required actions to start the guiding process. PHD2 must be started and configured before Ekos.

After launching PHD2, select your INDI equipment and set their options. From Ekos, connect to PHD2 by clicking Connect button. On startup, Ekos will attempt to automatically connect to PHD2. Once connection is established, you may begin the guiding immediately by click on the Guide button. PHD2 shall perform calibration if necessary. If dithering is selected, PHD2 shall be commanded to dither given the offset pixels indicated and once guiding is settled and stable, the capture process in Ekos shall resume.

 Ekos saves a CSV guide log data that can be useful for analysis of the mount's performance under ~/.local/share/kstars/guide_log.txt. This log is only available when using the built-in guider.


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