Star Tracker Polar Alignment in the Southern Hemisphere.

Star trackers are quite popular for landscape astrophotography. This kind of equatorial mount is key for capturing stunning landscapes with the Milky Way in the background. Unfortunately, setting up these special mounts can be challenging and frustrating for beginners.

Setting up a star tracker in the Northern Hemisphere is relatively easy, thanks to a bright star situated very close to the north celestial pole (Polaris). Unfortunately, there is no such bright star in the Southern Hemisphere, indicating the south celestial pole. The stars of the Octans constellation represent the closest equivalent to Polaris, but they are within the human eyesight limit, even in a dark and clear sky.

In addition to that, there are situations where there is no visual access to Polaris or Octans asterism because of a mountain, building, trees, light pollution, etc. Limiting the compositions and the scenarios that you want to capture just because of that seems entirely unreasonable.

In this article, I’m going to describe a process that not only makes this process easier and faster but also makes it possible when the celestial pole is not visible. This process does not require having visual access to Polaris or Octans asterism. It provides a reasonable alignment accuracy for visual telescopes and for astrophotography with short focal lengths. Obviously, if you have visual access to the celestial pole, you can improve the accuracy of your alignment.

If you want to use an equatorial mount for astrophotography with a telescope or long focal length lens, this process will help you in the initial alignment, but you should consider using an additional step to achieve better accuracy. Visit the SharpCap[1] or StellarMate[2] polar alignment documentation for more information. DSO astrophotography with a telescope also requires a guiding system to correct periodic errors of the mount.

Requirements

You need just a few inexpensive accessories to achieve a painless polar alignment.

• Install in your smartphone PS Align Pro (iOS), PolarAligner Pro (Android), or PhotoPills (less accurate).

• Skylabs Polar Alignment Adapter.

I previously used a rectified timber with a Vixen dovetail section and four silicone stickers to hold the smartphone. It worked reasonably well, but finally, I decided to design my own adapter to achieve better results. That particular design allows me to use a standard smartphone with a protective case and it also supports QHY PoleMaster. It is compatible with any telescope mount and star tracker with a Vixen dovetail or a 3/8” screw. The model works in the Southern and also Northern Hemispheres. You can order this adapter from the Skylabs NZ website.

Please, note that if your smartphone case is not flat, it may introduce some accuracy issues. In that case, consider removing your phone from the protective case to align your equatorial mount.

This device supports six different setups attending to the type of equatorial mount and the smartphone app / QHY PoleMaster. Check the following diagram to learn what option works best for your equatorial mount.

Instructions

Set up the star tracker as usual and point to the celestial pole using the smartphone compass.

1. Star Tracker Levelling and Rough Alignment

1. Level the tripod using the bubble level of the mount.

2. Unscrew the azimuth screws to give more range during the alignment.

3. Introduce the smartphone adapter to the equatorial mount dovetail bracket or 3/8" screw.

4. Introduce the smartphone in the adapter.

2a. Polar Scope Alignment App (iOS)

1. Place the phone parallel to the polar axis.

2. Open the PS Align Pro App.

3. Click on the three dots located in the bottom-right corner.

4. Select the Daytime/No Polar scope alignment (Sun symbol).

5. Move the mount with the AZ screws until the cross moves just in the middle of the circle.

2b. PolarAligner Pro App (Android) - suitable only for the northern hemisphere

1. Place the phone parallel to the polar axis.

2. Open the PolarAligner Pro App.

3. Click on the level button.

4. Use the azimuth screws to tune the alignment with the pole.

5. Click on the mount text in order to adjust the RA axis.

2c. PhotoPills App (iPhone and Android)

1. Place the phone facing the polar axis.

2. Open the PhotoPills App.

3. Click on the "Spot Stars".

4. Click on the AR button.

5. Use the azimuth screws to tune the alignment with the opposite pole.

6. Click on the mount text in order to adjust the RA axis.

3. Further Accuracy

If you have followed the previous instructions, you should have quite a reasonably good polar alignment. The described process works quite well for wide lenses (8mm to 50mm). If you have visual access to Polaris or Octans asterism, then those stars should be already visible through the polar scope.

The following steps will give you even better accuracy in your alignment.

1. Take your smartphone from the adapter and open the “Polar Scope Alignment Pro” or “PolarAligner Pro App” again.

2. Change the polar scope reticle with the one that you have. In my case, Skywatcher.

3. Rotate the RA axis until the polar scope reticle aligns with the image you can see in your app.

4. Move AZ screws and move Polaris or the Octans asterism into the right place.

Alternatively, if you have a QHY PoleMaster, you can slide it into the big hole of the adapter and secure it with the nylon screw. Then you can follow the user guide instructions as usual. The QHY PoleMaster is very handy because it's a very portable solution. If you are using a laptop with SharpCap or StellarMate (or similar) during your sessions, you can get even better accuracy with the mentioned software packages.

4. Test Drift and Accuracy

To assess your polar alignment’s accuracy, you can point your telescope or lens to a bright star from the East. Take a long exposure (~5 minutes) and review it with your camera or computer if there is any evident drift. The longer the focal length, and the longer the exposure, the more challenging it will be for your mount to track the stars. In that case, you should consider guiding tools for correcting the tracking.

Other tutorials and strategies

1. https://www.sharpcap.co.uk/sharpcap/features/polar-alignment

2. https://www.stellarmate.com/support/ekos/align.html

3. https://www.bas.asn.au/equipment/instructional-videos/

4. https://astrobackyard.com/polar-alignment/

5. http://astropixels.com/main/polaralignment.html

Do you want to learn more?

Consider enrolling in our landscape astrophotography course!