Position of the stars?

Question

If the solar system revolves around the galactic disk, and other star system revolve at different speeds, why don't their positions change?

Answer 1

These kind of positional changes are called "proper motion" and are measured in milliarcseconds per year. A milliarcsecond is 1/3,600,000 of one degree. That's how tiny these motions are. Stars with very fast proper motions might move as much as 1000 milliarcseconds per year, but most are slower than that.

To correct some errors by previous posters: it takes our solar system about 200,000 years to orbit the galactic center once (not millions of years); and the bright star with the greatest proper motion is not Arcturus, but Alpha Centauri.

Answer 2

Galaxies are large. Our own Galaxy is large. It is a spiral, four or five arms (depending how you count).

ALL the stars we see as individual stars belong to the same arm as the Sun (called the Orion arm -- some say that it is not a real arm, just a segment). All these stars orbit the centre of the Galaxy at roughly the same speed of 220 km/s.

Of course, there are "minor" differences in each individual star's actual speed (as in the phrase: You Mileage May Vary) and, over many generations, we have been able to note some (very small) changes.

Answer 3

O they're changing, at speeds of up to hundreds of miles per second, yet since their distances away are in the dozens of trillions of miles ( 1 light-year is about 6 trillion miles), the changes appear very slow. For example, assume a close star, say 10 light years away that was moving at a right angle to us at say 100 miles per second. For it to move 1 degree from our point of view, it will have to travel about 1 trilllion miles. At 100 miles per second, that's 10^10seconds, which divided by 60 is about 167 million minutes, which divided by 60 again is about 2.78 million hours which divided by 24 is about 116,000 days which divided by 365 is about 317 years.

Make sense?

Answer 4

They do, but because of the vast distances they change very slowly. It takes millions of years for the Sun to orbit the galaxy once, so it takes thousands of years for the positions of the stars to change enough to notice.

The motion of a star across the sky is called its proper motion. The star with the fastest proper motion is Barnard's Star, which is too dim to eve see without a telescope. It takes well over 300 years to move one degree.

Answer 5

Their actual positions change constantly and they are moving at incredibly high speeds, but the distances are so tremendous that they do not appear to be moving. And don't forget that we are moving as well in the same way, so our relative positions cause the motion to appear even more slow.

Answer 6

The previous posters are correct. In fact scientists have shown that constellations from 10,000 years ago are represented in certain human constructions.

Answer 7

they do. further complicating matters is something called
PRECESSION OF THE EQUINOXES. look it up.