Polar finder use with an app

Alignment with pole finder with the aid of an app

After the successful pole finder adjustment, the north celestial pole is aimed via the pole finder. The North celestial pole must be centered in the middle of the pole finder. Since Polaris rotates around the North celestial pole, the pole finder must be adjusted via the telescope adjustment so that Polaris lies at a specific position of the circle drawn in the pole finder.

North celestial pole (red cross) and Polaris (thick white line right of it) [Source image: James Lee from Chester, NH, USA, CC BY 2.0, via Wikimedia, supplemented by markings]

Before the use of smartphones, the date discs on the pole finder were used for this purpose. Depending on the year, day and time, the pole finder could be rotated in the mount so that the correct position around the North celestial pole was set. Afterwards the telescope was aligned by the azimuth and pole height adjustment in such a way that the marking for Polaris lay directly on the star. The center of the pole finder was on the North celestial pole.

However, the markings on the discs are only valid for a few years, since Polaris shifts by one day every three years. This has made it necessary to look at maps and calculations to determine where Polaris is at the time of observation. This is complicated and can also easily lead to errors.

In the meantime, there are apps that provide considerable assistance. One of them is called "Polar Scope Align", developed by Dimitrios Kechagias. It shows the current position of Polaris in relation to the North celestial pole.

App „Polar Scope Align“ [https://apps.apple.com/de/app/polar-scope-align/id970157965, April 2021]

The pole finder is rotated in the mount as shown in the figure (the "6" at the bottom, the "12" at the top). Via the azimuth and pole height adjustment, Polaris is brought exactly to the position of the pole finder circle, as it can be seen in the app. The app takes into account that the image is rotated 180° by a pole finder due to its optical properties. Therefore, a rethinking is not necessary. In the illustration, Polaris is just before "12" when looking at the sky, and Polaris is just before "6" when looking through the pole finder.

As of version 3.4, a "Daytime / No Polarscope Alignment" has been added to the app, which makes it possible to align the telescope without a pole finder or during the day. The smartphone is attached to the mount for this purpose. The mount can be aligned via a target cross.

Target cross of the "Polar Scope Align" app for daytime alignment

This method is sufficiently accurate to observe the sun. If astrophotographic capturing is the goal, however, readjustment is still necessary because the smartphone sensors do not provide the required accuracy. (With the smartphone, an accuracy of just under one degree is achieved). [https://astro.ecuadors.net]

In addition, the smartphone is placed on the mount, which can be affected by surrounding magnetic metal. An adapter that is used to attach the smartphone and at the same time provides a distance to the magnetic metal parts is helpful here.

Adapter to attach the smartphone with simultaneous distance from magnetic metal parts