How To Polar Align A Telescope Mount During Daylight

For those of us who do astronomy, whether visually or for astrophotography, polar alignment is a procedure that we are familiar with, and have to do before every observing sessions, unless we have a permanent observatory.

There are several methods to do polar alignment, but they all work after dark. Whether it is centering Polaris in a polar scope, Celestron's All Star Polar Alignment (ASPA), QHY's PoleMaster, the more accurate but time consuming Drift Alignment, or DARV.

Since I am using the open source Onstep telescope controller, I use its 6-star align, with plate solving in KStars/Ekos, followed by the OnStep RefinePA feature, which involves de-centering a star, then manually re-centering it using the Alt and Az knobs, somewhat similar to Celestron's ASPA.

All the above methods rely on stars being visible, which can only be done after dark. At a minimum, it is 30 minutes after sunset.

But what do you do if you want to do polar alignment during daylight?

Why polar align during the day?

What? Polar align during daylight? Why is that helpful?

Well, you need to do that if you are observing the sun, for example, during an eclipse, or just viewing sunspots.

You also need it if you are observing a transit of Mercury, or even the transit of the International Space Station.

Needless to say, that any of that needs a special solar filter, otherwise it will damage your equipment or even your eyes.

The following is a list of methods that help you do a polar alignment

Scheiner's Method

Christoph Scheiner was a Jesuit priest and an astronomer. He observed the sun using a helioscope. He recorded and published his findings on sunspots as a result.

To align his helioscope, Scheiner devised a method, now known after him. This is a variant of the Declination Drift method, known as Drift Alignment if stars are used.

There is an Android app based on Scheiner's method, written by Wolfgang Strickling.

Using A Smart Phone

Smart phones these days have many sensors that can be used in various useful ways.

One such way is if your mount has a flat surface on its Right Ascension axis. If there is, then you can place a phone in the right way, and use a free planetarium application, such as KStars Lite, or Stellarium Mobile Free.

The idea is described here, and the goal is to center the 'other' celestial pole visually in the phone while lying flat at 90 degrees on the RA axis. For example, if you are in the northern
hemisphere, you view the planetarium, and center the south celestial pole on the phone's screen

For KStars Lite, you swap the top menu, then click the A icon to turn on the internal sensors, the Horizon icon to make the celestial map below the horizon visible, and the Equatorial Grid button. Zoom in and adjust the telescope's knobs to center the south celestial pole.

Similarly, with Stellarium Mobile Free, click the phone icon to turn on the sensors, click on the Landscape icon to turn the horizon off, and the Equatorial grid button. Point the phone up to enable sensor tracking, then press it against the flat surface perpendicular to the RA axis. Adjust the knobs until the south celestial pole is centered.

Align At Night, Then Park

One other method that can be practical in certain situations is to align at night, then park the telescope in a configuration that makes its alignment reproducible using a compass and a bubble level.

For example, in this Astro-Physics manual page 21, is that RA is level horizontally, and DEC = 90 - Latitude. The telescope is aligned north (or south in the southern hemisphere) using a compass.

Once the scope is unparked, you slew to the Sun, then sync on it.

Align During Daylight, Then Park

For a Vixen Porta Alt-Az mount, with OnStep, Keith Trivett shares the following procedure:

No need to put an optical tube on the mount.
Perform a 3 star align, and accept the positions as they are.
Park the mount horizontal (altitude 0) and pointing north (azimuth 0).

Then, to observe the following day (or thereafter), level the tripod, point scope north and set horizontal with bubble level. Update the location, date and time. Unpark and slew the sun, center and sync. The sun is always in the view finder after the goto and tracks fine. Remember to park up and its good to go the next time.

Do you have other methods? Please share them in the comments below.

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