3
$\begingroup$

I came across few sources that claim Polaris movement cannot be observed with the naked eye. But then, I saw images of the star trails (timelapse), and they clearly show Polaris not quite at the true north and moving around the Earth's axis with a radius that is very visible. See for instance the following images:

enter image description here

enter image description here

However, this image from Wikipedia does not show a trail for Polaris:

enter image description here

What am I missing here?

$\endgroup$
  • $\begingroup$ The exposure time of pictures seem to be different. $\endgroup$ – J. Chomel Apr 12 '18 at 6:49
  • $\begingroup$ FWIW Polaris is moving and at some future date ("you could look it up") it'll be well off geographic North. In the meantime, magnetic North is over 16 degrees off for us New Englanders. $\endgroup$ – Carl Witthoft Apr 12 '18 at 17:23
  • $\begingroup$ Mhmhsh, your other question was deleted but you might find this interesting: solar-center.stanford.edu/FAQ/Qsunasstar.html $\endgroup$ – userLTK May 5 '18 at 17:54
5
$\begingroup$

Does Polaris have a trail in the sky timelapse? Yes. Every star has a trail, but it's smaller if it's closer to the pole. Polaris is close to the pole but it's still 45 (arc)minutes away. I don't think it's visible with the naked eye; no star trail is visible with the naked eye as you only see one 'instance' of the sky. What perhaps would work, and is more feasible for stars closer to the celestial equator, is trying to see the movement of a star compared to an object on Earth, e.g. a tree, a building or the horizon.

The exposure times of the photos are different, as @J.Chomel notes in the comments. You can calculate the exposure time by looking at the arc length; in 23 hours and 56 minutes (a 'sidereal day'), a star will make a full circle.

The trails on the last photo have an arc length of about 8 degrees, corresponding to about 30 minutes; the first two photos are more like 9 resp. 5 hours. Also, the zoom factor (of the lens) may play a role; if a photo is zoomed in more, Polaris' movement is more likely to be visible. I'm not sure if this plays a role in this photos, though.

| improve this answer | |
$\endgroup$
3
$\begingroup$

Polaris is about 1 degree from the celestial North Pole. An image with sufficient magnification and sufficient exposure time will show a (short) trail for Polaris.

The difference between the images is the magnification and the exposure time and Magnification. The first image appears to have been about 10 hour exposure (actually a multiple exposure) The Last one appears to be 30 minutes or less. The first has also been magnified more than the last. The result is that the trail of Polaris is just too short to be visible in the last image.

| improve this answer | |
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.