The motion of stars?

Question

If I were to keep track of a star's movement in the east and another star in the west, once a week at relatively the same time, how many degrees would the star appear to move? Also do they appear to be higher or lower in the sky?

Answer 1

The short answer to your question is that each week, the eastern star would be 7 degrees higher and the western star would be 7 degrees lower. The how and why of this is so much more interesting so I will elaborate.

If you go out at the same time each night you will find all the stars shifted to the west by about one degree (more precisely its 360/365.25 degrees). The reason for this is that our day, and our timekeeping is based on the rotation of the Earth relative to the Sun. On the average, midnight occurs when you are on the part of the Earth directly opposite the Sun. That means that the point directly overhead at midnight is in a straight line from the Sun to the Earth and beyond. Call this first observation January 1st. Of course, the stars you see overhead then are in that region of sky where the Sun-Earth line points. Three months later (1/4 year) on April 1st, the Earth has moved around the Sun so the Sun-Earth straight line now points in a direction 90 degrees (1/4 revolution) from where it was 3 months ago. You see a new set of stars over head and your January stars are 90 degrees to the west, putting them on the western horizon. Another 3 months to July 1st and your April stars are setting in the west. Yet another 3 months to October 1st and the July stars are setting. By now it is only 3 months to January 1st so the January stars are 90 degrees away from overhead. So they are rising in the east as the October stars are overhead, the July stars are setting and the April stars are on the other side of the world, hidden behind the Sun.

Answer 2

They would move about a degree per day because the Earth completes one 360 degree circuit around the Sun every 365 1/4 days. This motion makes the Sun appear to move against the background of stars, but since time is measured by the Sun, the stars will appear to move if you look at them only once a day at the same time.

Answer 3

You probably wouldn't notice any variation in the degrees of separation of the stars, unless you watched them for thousands of years. If you mean on a single night, then they would appear to move uniformly with each other, and thus would always be at an equal distance. However, you would notice them moving higher and lower in the celestial sphere in correlation with the seasons, much like the sun. But, if you are observing two stars in the summer, they will not be in the night sky in the winter.

Answer 4

I worked for N.A.S.A 17 yrs. I reduced many star shots and the star charts were taken in the 1898 time from glass plates and I never found a star that was out of place.

Answer 5

The question needs a period of time in which you are measuring weekly movement for. & where on the earth you are observing from and what month of the year.