Polaris Distance from Celestial Pole

If you've taken star trails photos facing north, or used Polaris to calculate latitude, you're probably aware that the North Star doesn't sit directly over the north celestial pole. But how far off is it?

My trails are a little wonky because my tripod was on a wooden balcony, 300mm zoom lens, field of view in this image is about 3.5°

In the above photo, Polaris is the brightest line in the center of the image. You'll notice that there are quite a few stars in between Polaris and the true celestial pole. However, none of these stars are bright enough to be reliably visible, and aren't used for naked eye navigation or basic polar alignment.

Polaris lies 0° 40' 37" from the celestial pole

Polaris' position in the sky is moving toward the pole, making it a better pole star by the day! In the year 2000, Polaris was located at 89° 15' 50.8", and is now (according to Stellarium) located at 89° 19' 23".

I thought it would be a relatively simple question to answer "how far is Polaris from the celestial pole" but now I've been looking up terms and reading about things like parallax, precession, nutation, aberration, and proper motion. Wow! So much to learn still.

So in the year 2000 at exactly noon (terrestrial time) on January 1st, the position of stars was calculated as the new standard for the next 50 years. This is called J2000.0 denoting Julian date 2451545.0 TT. I still can't find a good description of the difference between equinox and epoch, but nevertheless right ascension and declination are constantly changing, so the epoch servers as a standard starting point for calculations.

This is getting a bit heavy, so I'll wrap up by saying that since the reported "to date" position of Polaris is 89° 19' 23" all we need to do is subtract from the celestial pole 90° 00' 00", which (be sure to borrow units of 60) comes out to 0° 40' 37" (or 40 and 37/60 arc minutes = 40.6166 arc minutes).

Don't take my word for it, kids! I never took a class on this, I'm just sort of thinking out loud trying to figure all this stuff out.

Two hour star trails before and after color correction

I took these 210 images at ISO 800 for 15 sec each using my point and shoot camera with the shutter taped down. I'm so sick of light pollution, but I'm also sick of jacking up the contrast to make my photos look cool - so I couldn't decide which one to post.

Color-corrected and contrast adjusted version

Original stacked image with yellowish light pollution at ISO 800

Which one is more "real," the one that looks more like a red brick building and night sky, or the one that was untouched out of the camera (after stacking of course).

What's with the checkerboard JPG compression in this post? Below is a PNG version to compare. Ugh, it's always something!

This two hour stack is long enough to illustrate that Polaris, the North Star, is not at the actual celestial pole. The curved trail shows that it is very close to the pole (within 1º), but if the star were perfectly aligned with the pole it wouldn't make a trail at all! 

Green dot added to show approximate location of true celestial north pole

Double star in the Big Dipper handle with labels

It's supposed to rain for the next 5 days here in Bowling Green, but I feel the need to blog! Blogging is a great way to learn, because to make sure I don't just talk out my ass I have to actually look things up to write about them. I bet to real amateur astronomers this is just silly, but I'm a noob and having a blast teaching myself what I can!

Tonight I decided to pull up a 15 sec exposure of the northern sky from Sunday night when I made my star circle image. I remember Dale Smith from the BGSU Planetarium asking if we could spot the double star in the handle of the Big Dipper (apparently a Native American test of good eyesight). I was able to just barely make out the double star with the naked eye, but I'm pleased that they are visible even with this quick snapshot. 

For some reason, the stars near the edge seem to smear more during a 15 sec exposure than the ones in the middle. 

The stars are called Mizar (the larger one) and Alcor (the smaller one). Mizar is actually a double star itself, making this "star" in the handle of the Big Dipper an interesting combination of three. For much better images and explanations, head over to AstroPix.com. But wait! The images by Jerry Lodriguss show that this small point in the sky actually has 4 stars with the addition of the very faint Sidus Ludoviciana. It's as if somebody bejeweled rhinestones to the handle of our celestial saucepan! 

Finally, you'll notice that Polaris is easy to locate by drawing an imaginary line through Merak and Dubhe at the large end of the dipper bowl. They don't exactly line up, but in the open sky it's a very hard to miss the obvious Polaris (48th brightest star in the sky).