Why does a pole star appear as a spot when others show a track?

Answer 1

The pole star, also known as the north star, is straight above the axis of the earth. If you take a picture with an open iris for a bit of time, all the other stars move, showing a blur or a line. Since the north star is above the axis, it remains a point of light and not a line.

As the earth revolves in its orbit around the sun, it acts like a gigantic gyroscope. The tilt in the pole is always oriented (with some complex variations that can't be covered here) toward the pole star. The star is so far away that the width of earth's orbit doesn't have a great effect on the star's position in our sky. The pole star does appear to move a little. It is very close to the celestial position of the north pole, but it is not exactly on the point.

Unfortunately the Southern Hemisphere is not blessed with a South Star despite the extraordinary display we see as we look in towards the ~ centre of the galaxy.

The Earth is near the outer edge of the galaxy but the North or Polar Star, is even further out.

Circumpolar stars are stars that never set. These types of stars are found at the poles of the Earth. They do not set because of their location at the pole or top and bottom of the Earth. Picture a globe and put your hand above the top of it and spin it. If you where standing on top of the globe your hand would always be visible even though the globe is spinning. Now put your hand off to the side, and imagine you where standing on the side. The star [your hand] would stay in place and you would go around the globe and not be able to see your hand when your on the other side of the globe.

The Pole Star is lined up with the Earth's axis so it always apparently stays in the same direction as the Earth rotates and we revolve with it. All the other stars appear to rotate anticlockwise round it (in the northern hemisphere).

Answer 2

There's no fundamental reason a bright star should exist in line with the Earth's axis of rotation, and actually the Earth wobbles very slowly (precession) over a period of about 26,000 years, so the fact that there's a fairly bright star almost directly over the north pole at this particular time is purely coincidence. Right now, the pole star is Polaris (alpha UMi), but 2500 years ago, the pole star was Kochab (beta UMi) at the other end of the Little Dipper and 4700 years ago it was Thuban (alpha Dra). 12000 years from now the pole star will be Vega (alpha Lyr), though it won't be nearly as close to the pole as Polaris is now (neither was Kochab). There isn't a bright star over the south pole. Sigma Oct is fairly close, but with an apparent magnitude of 5.5 it's barely visible even on a clear night.