Polar Alignment

This feature helps you align an equatorial mount to Earth's rotational axis. It will also work with other similar instruments such as equatorial platforms, barn-door mounts, etc.

What is Polar Alignment?

Due to Earth's rotation around its axis, the objects in a telescope's or camera's field of view will appear to move even though the telescope itself might be stationary. To compensate for this motion, a corresponding movement needs to be made on the mount. This compensatory movement is called tracking.

To help with tracking, equatorial mounts and similar instruments have an axis that is aligned with the Earth's axis of rotation. The lesser the alignment error, the lesser will be the tracking error.

Let's define RA axis of mount as the axis on which the mount is intended to rotate such that only the Right Ascension of the target changes. This is the axis that needs to align with the Earth's rotational axis, which is marked by the two Celestial poles.

Similarly, the Declination axis of mount is the axis on which the mount is intended to rotate such that only the Declination of the target changes.

How to Polar Align

To Polar Align with this app, follow the steps below.

Checklist

  • Ensure the location in the app is set accurately.
  • Ensure Plate solving is working. See this page for more details.
  • Make a rough alignment. While not strictly necessary, it will help reduce ambiguities. An alignment within 45° of the celestial poles is good enough.
  • Physically attach the Android device to the OTA or mount. It can be attached in any convenient orientation, as long as the camera points towards the sky.

Start the alignment

  • In the live view screen, press pause, and bring up the Menu
  • Click Start polar alignment button
  • You will be greeted by a screen such as the one shown below.

PolarAlignBegin

  • You will be walked through a number of steps, including,
    • Locking the declination axis
    • Rotating on the RA axis
    • Locking the RA axis as well
    • And finally, the alignment screen shown below:

PolarAlignGuide

This screen indicates the degrees by which the mount needs to be adjusted, so that it is fully aligned. While you move the mount, the screen keeps updating with the latest measurements.

When you are happy with the alignment, you can click the Done button to exit.