How to Polar Align Without Polaris
You might have wondered how to polar align without Polaris when Polaris (the North Star) or the region around the Southern Celestial Pole is not visible.
Polar alignment is the process of aligning the right ascension axis of an equatorial mount telescope or camera tracking mount with the celestial pole in order to accurately track and photograph celestial objects.
If Polaris is not visible due to factors such as light pollution, obstruction by buildings, clouds, or trees, you can use alternative methods to polar align your equatorial mount.
Compass and protractor
While not as accurate as other methods, you can use a compass and a protractor to roughly align your equatorial mount with the North or South direction, depending on your hemisphere.
This can serve as a rough initial alignment, and you can then fine-tune it using other methods.
This method can also be useful (if not the only one available) for polar alignment during the daytime, like when shooting solar eclipses and you have to travel to a remote location without the opportunity to align your mount the night before the eclipse.
Prior to using this method, you need to know the latitude and the magnetic declination (the offset between the magnetic North Pole shown by the compass and the celestial pole) of your location.
There are apps (like Polar Scope Align Pro) that will tell you the magnetic declination for any location on Earth.
First, make sure the head of your mount is as level as possible. Most equatorial mounts will have a bubble level; use it to level the mount head.
You can use a classic magnetic compass or the compass on your phone (some compass apps should be able to correct for magnetic declination too).
In case you use a magnetic compass, be careful not to have it too close to any metallic part of the mount as that will affect the reading. Smartphones are usually pretty well shielded, and metal will not affect them that much.
You will use the protractor to set the angle of the right ascension axis of your mount. Latitude is equal to the angle of the celestial pole above the horizon.
Most mounts will have a protractor printed on the wedge; if that scale is not visible or is not there by design, use a classic protractor for measuring angles.
Polar alignment apps
There are several smartphone apps available that can help you polar align your equatorial mount without relying on Polaris.
These apps use your device’s built-in sensors, such as gyros and accelerometers, to calculate the position of the celestial pole even when Polaris is not visible. Polar Scope Align Pro (iOS) and Polar Aligner Pro (Android) are probably the best apps in the field.
Simply follow the instructions provided by the app to adjust your equatorial mount’s altitude and azimuth until it aligns with the calculated position of the celestial pole.
They even have a mode that allows you to roughly polar align your mount during the daytime.
This method requires patience and practice but can be used when Polaris (or the region around the Southern Celestial Pole) is not visible.
In the beginning, it will not be very easy to remember all the steps involved in drift alignment, so it might be a good idea to print them out.
Here’s a step-by-step guide on how to perform drift alignment:
- Set up your equatorial mount and telescope as you normally would, ensuring that the mount is roughly levelled and pointing towards the general direction of the celestial pole (you can use any of the previous two methods to achieve this).
- Choose a suitable star for drift alignment. Ideally, you should choose a star that is near the meridian (the imaginary line that runs from due north to due south through the zenith) and is located at least 30 degrees above the horizon. A star with a declination close to the celestial equator (0-20 degrees) is preferred, as it will show the most noticeable drift.
- Center the chosen star in your telescope’s eyepiece or camera’s field of view. Use high magnification if possible to make it easier to observe the star’s motion. In case you use a telescope, a reticle eyepiece will be of great help. Now, figure out which way is east and west in the eyepiece. Turn tracking off and see in which direction stars drift. That will be west. Then find where north is by nudging your telescope towards the north on the declination axis. In case you use a reticle eyepiece, align the wires of the reticle with the cardinal points.
- Turn tracking on and start monitoring the star’s motion over a few minutes. In the case of using an autoguider, turn it off.
- Observe the direction of the star’s apparent motion. If the star drifts north, you have to move the azimuth so that the star appears to move east as in the following diagram:
Of course, if the star drifts south, you’ll have to move the azimuth west instead. Keep on doing this until there’s no noticeable drift for at least 5 minutes.
- Once you’ve got the azimuth aligned, you need to align the altitude. Find a star about 10 degrees above the western horizon in the same declination range as the first star (0-20 degrees). Compared to the azimuth, the altitude is way more intuitive. Line the star up on the east-west reticle line and wait. If the star drifts up, adjust the altitude so that the star appears to move down in the eyepiece. If the star appears to drift down, adjust the altitude so that it appears to move up in the eyepiece. Again, do this until the star doesn’t drift off the line for at least 5 minutes.
- Once you have achieved minimal drift, your equatorial mount is now accurately polar aligned. Lock down your mount’s altitude and azimuth adjustments to secure the alignment.
If you’re in the southern hemisphere, you’ll have to reverse South for North and East for West.
Drift alignment can be a challenging technique that requires patience and practice, but it results in very precise polar alignment, which is crucial for accurate tracking and long-exposure astrophotography.
Most of the time, you will not need to be as accurate as this.
Very accurate drift alignment is needed when you polar align the mount of a permanent observatory.
For the astrophotographer on the move, using just a star tracker and a short focal length lens and looking for relatively short exposures (let’s say below 2 minutes), it’s enough to align the mount using the compass and protractor method.