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Astronomy/North Star

Question
QUESTION: Dear Courtney,
Please can you tell me if the location of the North Star is in fact pure North. That is to say is it North of the whole world considering it is so far away from earth ? I know the earth rotates and in summer in the upper tropic of cancer we are nearer the sun, so we must be "leaning" off center. Does this affect how we see the North Star ? Also as I view the sun throughout the day going east to west (the earth going west to east)and draw a line indicating it's path it shows to me that the North Star that night is in face not pure north, but more like NNE, like 1 o'clock on clock face ? Finally, about how far away is the North Star ? Thank you for taking my question.

ANSWER: Polaris is less than three quarters of a degree from the Celestial Pole, which defines true north. This is a small enough distance that if you hold your arm out and point at it with one of your fingers, just the width of your finger at arm's length is larger than the circle Polaris follows around the Pole during the course of a day (and night).

Your idea of following the Sun's path should have given you the direction of true south, which is almost exactly halfway between the rising and setting points of the Sun on any given day. So Polaris should have appeared to you to be in exactly the opposite direction. I don't know why you ended up with a noticeably different direction.

The tilt of our axis relative to our orbit changes the appearance of the Sun's path during the year, but it does not affect the apparent position of Polaris, because the Pole itself points in the same direction throughout the year.

There are very small variations in the direction of the Pole during the course of a year due to the tug of the Moon and Sun on our equatorial bulge, but they are too small to notice without extremely careful measurements. There are much larger changes over very long periods of time, but when I say very long I mean much longer than a human lifetime. (The path of the Pole in the sky is shown on my page about the constellation of Ursa Minor, at http://cseligman.com/text/atlas/ursaminor.htm )

The distance of Polaris is only roughly known. It is probably a little less than 400 light years away. But even if it were as close as the closest star (other than the Sun) any change in its apparent position due to our motion around the Sun would be over a hundred times smaller than the smallest dot most people can see (even the best naked-eye astronomer in history, Tycho Brahe, would have needed eyesight more than 50 times sharper to see the change in position of even the closest star). Just the size of the apparent disc of Polaris as seen through a telescope (which is an illusion caused by the fact that bright stars look bigger simply because they are brighter, not because they are really bigger) is hundreds of times larger than the change in its position due to our motion around the Sun. So Polaris, save for the fact that it goes around the Celestial Pole instead of being exactly at the Celestial Pole, is north for everyone on Earth no matter where they are on Earth or where we are in our orbit.

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QUESTION: Thank you for such a prompt and brilliant answer. Here in this part of the world we look to the "Plough" and five times the distance between the front two stars of this group is where we think the North Star is approximately. Am I looking at the wrong star perhaps ?? Thank you sincerely,
Aidan

It sounds like you're looking at the right star, but there is another star of equal brightness (Kochab) that is at the other end of the "Little Dipper", so it's possible that you are looking at the wrong one. Although labeled as the Big and Little Dipper instead of the (Large and Small?) Plough, the two constellations and their relative positions are shown partway down my (incomplete) webpage about Stars and Constellations (at http://cseligman.com/text/sky/constellations.htm ). One interesting thing about Kochab is that it was the Pole Star in ancient times, as shown in the diagram of the movement of the Celestial Pole on the page (http://cseligman.com/text/atlas/ursaminor.htm ) about Ursa Minor.
Questioner's Rating
 Rating(1-10) Knowledgeability = 10 Clarity of Response = 10 Politeness = 10 Comment Courtney Seligman Thank you very much for your relies to me. Explanationr super. Now I'm more interested in the stars thanks to you ! Please keep up your wonderful work. Thanks again.

Astronomy

Volunteer

Courtney Seligman

Expertise

I can answer almost any question about astronomy and related sciences, such as physics and geology. I will not answer questions about astrology and similar pseudo-scientific rubbish.

Experience

I have been a professor of astronomy for over 40 years, and am working on an online text/encyclopedia of astronomy, and an online catalog of NGC/IC objects.

Publications
Astronomical Journal, Publications of the Astronomical Society of the Pacific (too long ago to be really relevant, but you could search for Courtney Seligman on Google Scholar)

Education/Credentials
I received a BA in astronomy and physics and a MA in astronomy, both from UCLA. I was working on my doctoral dissertation when I started teaching, and discovered that I preferred teaching to research.

Awards and Honors
(too long ago to be relevant, but Phi Beta Kappa and Sigma Xi still keep trying to get me to become a paying member)