We’ve all seen amazing astro photos created by ‘amateur’ astronomers. Some are on par with the finest works of professional observatories just a few years ago. What’s their secret? Well, there are a number of secrets… more than can go into a single blog post. First, there have been amazing breakthroughs in CCD technology in the last several years. Combine this with dramatic price reductions and high end astrocams are within reach of many an aspiring astrophotographer. But, guess what? The finest CCD camera on the market all by itself isn’t enough to catapult you to the top tier of the astrophotography world.

Secondly, the degree of control available to astrophotographers through the latest image processing software programs is unrivaled. With an off the shelf computer and off the shelf image processing software, aspiring astrophotographers can coax an almost unimaginable amount of detail from raw images. Additionally, many kinds of ‘mistakes’ can be cleaned up with these programs. Still, with just the latest copy of Photoshop, you won’t find yourself among the top tier of astrophotographers.

I’ve saved arguably the best and most important component of high-end astrophotography for last. Polar alignment. Without a precise polar alignment, your hopes of taking the spectacular images that’ll end up in Sky and Telescope or on the APOD simply aren’t going to happen. Sure, you can get lucky and shoot some phenomenal passing event. I know, I’ve been lucky a few times I’ll certainly take luck over skill any day. But, that said… if you want to take seriously amazing deep sky images, you must have an absolutely spot on polar alignment. Skip this step and you’re doomed to ‘nice’ shots… but not truly amazing.

Polar alignment involves adjusting your telescope’s mount such that the polar axis of the mount is pointing at the north celestial pole. Huh? Ok, its not as complicated a concept as it might sound. Let’s think this through. We all know that objects in the sky (sun, moon, stars) seem to rise in the east and set in the west. This phenomenon is caused by the Earth’s rotation. Earth is spinning on its axis and astronomical objects (not bound to the Earth) are seen to move because of this. The polar axis of your mount (when aimed properly) corresponds to the axis upon which the Earth turns as it rotates. Simple, right? When properly polar aligned, your mount only needs to make use of one of its two motors to keep the image centered. The RA (Right Ascension) gears compensate for the Earth’s rotation and keep your image centered in the eyepiece or in the camera’s field of view. If your alignment is off, the mount needs to make corrections on two axis. This is almost impossible to do with incredible precision. For visual use, this really isn’t even a critical issue. Simply eyeballing the telescope’s direction as north is ok. For lunar or planetary images you might even stop at this point. However, for deep sky images, you’ll need to go the extra mile to get your scope precisely polar aligned.

Ok, so how do we actually go about precisely polar aligning your mount? First, get the scope roughly polar aligned. Simply pointing the mount’s polar axis to the north star (Polaris) is a good first step. Next, you’ll want to make use of the ‘drift method’ of alignment. The drift method is a technique whereby you point at a couple of specific stars and watch the star drift out of the center of your eyepiece over time. Hence, the name. Adjustments are then made to the mount itself to bring you closer to alignment. This processes is repeated until there is no more drift. Note, that as you fix one axis, you can be slightly messing up the other, hence the iterative nature of this adjustment.

Azimuth Adjustment

To proceed, choose a star near the intersection of the meridian and the celestial equator. The closer the better. I’ve seen references say you should be within 1/2 hour of Right Ascension and 5* of declination. I’m not sure how these tolerances were picked, but I’ve tried my best to follow them. You’ll find that at times, this is easier said than done. Sometimes, there simply aren’t any bright stars in those areas. A goto scope and some good astronomical software will be helpful to find these points (you’ll need a pretty accurate pointing model to find these). To get the stars perfectly centered, you’ll need an illumated reticle eyepiece. I have a non-illuminated one at the moment and usually have to use a red light to help me see the lines that crisscross the eyepiece. Accuracy here is pretty important. Additionally, the higher the power your setup the better. So, either get a very small focal length eyepiece… use a barlow… or both. The higher the power, the faster you’ll notice the drift and the more closely you can watch for improvements.

For this star, you’ll only be making adjustments in azimuth. If the star drifts to the south, adjust your polar axis to the west. If the star drifts to the north, adjust the polar axis to the east.

I like to try to use a consistent time period for the drift, say 2 minutes. This way, you’ll start to get a feel for how quickly your improving things. If you drift out of the eyepiece in 2 minutes the first time, and then only 1/2 way out of the eyepiece the second time, you know that you’re making good adjustments and should have things nailed shortly.  If you use widely divergent intervals, its much harder to gauge how you’re progressing. You can still do it, but it starts to feel much more hit or miss. I usually like to get 3 or 4 iterations on this star before doing an about face.

Additional Resources:

Celestron

Jerry Lodriguss