Moravian instruments, Inc., source: https://www.gxccd.com/art?id=789&lang=409, printed: 21.07.2026 15:35:21

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20.7.2026
SIPS Mount Polar Alignment tool
 While the commonly used polar axis viewfinders, supplied with many mounts, may help to achieve polar alignment of equatorial mounts sufficient for visual observations, astro-photography or research applications (e.g. variable star observations etc.) could benefit from more precise mount polar alignment, achievable e.g. using drift method. But this method is quite time-consuming, and its precision is also limited due to refraction changes when a monitored star rises or descends during adjustment. Faster and more precise polar axis adjustment is a big help for more precise telescope go-to and star tracking and it is a necessity especially for permanent (observatory) setups.

To help with precise equatorial mount polar alignment is a task for the new SIPS Polar Alignment tool, introduced in SIPS v4.5. The align procedure is based on imaging of the pole with the main camera. To function properly, several prerequisites need to be satisfied:

  1. Main imaging camera must be connected and online. If you want to use the Guiding camera for pole align, temporarily select it as the main Imaging camera.

  2. Astrometry of images, acquired with the main camera, must be properly working. This means the Star search parameters must be defined to find even the brightest stars within field of view, astrometry catalog must be selected etc. The Astrometry tool should be used to configure and test plate solution of acquired images prior to polar alignment.

  3. Exposure time must be set so the image contains enough stars to allow astrometry (acquiring just Polaris is not enough).

  4. The celestial pole must be visible from the observing site, and the equatorial mount must be at last roughly aligned to the pole, so the real pole remains in the field of view even if the telescope is rotated in the R.A. axis.

  5. If the algorithm should count with the atmospheric refraction (required for sub-arcminute alignment precision), the observing side location must be defined in the Observatory Setup dialog.

Equatorial mount pole align dialog box

The dialog box offers several steps, allowing to determine actual position of the mount polar axis and its adjustment, so it precisely points to the celestial pole.

Step 1: Introduction

The first screen of the mount alignment dialog box summarizes these prerequisites. It also allows to choose if the algorithm should count with refraction.

Hint:

To properly calculate refraction, SIPS needs to know the site geographic latitude. The Polar alignment dialog box relies on the value specified in the Observatory Setup dialog box, instead of yet another latitude definition controls. If the Count with refraction check box remains disabled, the observing site geographical location is not defined properly.

Remark:

SIPS currently does not allow specification of actual temperature and atmospheric pressure, which also affect the refraction. Instead, SIPS calculates refraction for temperature 10 °C and pressure 101 kPa. However, temperature change for 5 °C affects the refraction by approx. 1”. Refraction changes caused atmospheric pressure are more prominent, but still typically remain well below uncertainty often defined simply by mechanical deformations of mount polar axis locking screws, which is typically around 5” even for very robust and high-quality mounts.

Step 2: Pole Shot One

When the mount points the telescope to the pole, SIPS needs to perform an exposure and calculate its astrometry. Set exposure time properly so the image contains enough stars allowing astrometric reduction. SIPS calculates the location of the apparent pole (this means the pole as projected by refraction) and highlights it in the image.

If the refraction is to be included in calculations, also the position of the real pole (where the pole would be seen is there is no atmosphere).

Hint:

The Polar adjustment dialog box runs modally, so no other controls are accessible. This is why the Image Zoom control is available withing the dialog box. Also, the mouse wheel image zooming is propagated to the image view and can be used to find a desired visible sub-frame from the whole image.

Step 3: Mount rotation

In the next step, SIPS needs to determine where the R.A. axis of the mount actually points. This is done by rotation the mount around the R.A. axis. The rotation angle is not that important; however, it should be large enough to allow calculation of the rotation center with enough precision. Angle close to 90° is optimal, but any angle between 60° and 120° should work as well.

Step 4: Pole Shot Two

Another exposure of the imaging camera allows SIPS to determine rotation center.

Step 5: R.A. Axis Adjustment

The desired state is the mount rotation center and the celestial pole overlaps. Use the final step of the Pole alignment dialog box to start exposures, process them and display actual angular deviation between the pole and the mount rotation axis. The distance is shown in the Deviation field. Also, the deviation is displayed within the image.

SIPS also calculates and displays the projection of the angular deviation into Azimuth and Altitude part. As the mount polar axis adjustment is typically done separately in azimuth and altitude, seeing deviations in both coordinates independently helps with the adjustment.

Hint:

SIPS does not distinguish negative and positive directions in both axes, as different mounts use different placement of adjustment elements—sometimes the user observes the mount from southern direction, sometimes from northern direction etc. Using the trial-and-error (move the mount in one direction and check if the deviation increases or decreases) proves to be more effective than keeping track of what direction is interpreted as positive and which is negative.

There is only one celestial pole displayed in this step. If the refraction is included in calculation, only the real pole position is shown. Otherwise, only the apparent pole is used.

The dialog allows to check the Repeat exposures option, which initiates next exposure, including the astrometry processing and calculation of celestial pole position and deviation. The next exposure is started after the defined Delay between images, which is intended for actual R.A. axis adjustment.

The best achievable pole adjustment precision depends largely on the robustness, stability and precision of the used mount and its adjustment mechanism.

  • Deviation < 15” is excellent. Such deviation should not meaningfully affect the telescope go-to precision or tracking accuracy.

  • Deviation < 1’ is good. Any go-to or tracking uncertainties should be easily compensated by precision go-to (multi-step go-to including plate solving and mount syncing) and guiding. At least, this precision should be achieved on permanent setups (observatories).

  • Deviation < 5’ is acceptable, especially for portable and ad-hoc setups. Higher pole adjustment deviation may negatively affect mount functions.