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Motion of the Stars in the Night Sky

-- | September 16, 2015

Question: Why do we see the same stars every day of the year in there same location when we orbit? No way does the Cosmo’s move with us. — Mike

Answer: In fact, the stars that one can see in the night sky on any given night change as the Earth moves along its orbit around the Sun. You can test this yourself by noting the location of a bright star on one night at a specific time. Come back a few weeks later at the same time and note the position of the same bright star. You will find that the star has moved a bit to the west from its previous location. This is due to the fact that the Earth has moved a bit along its orbit, which presents a somewhat different view of the stars in our night sky than it did previously. If you wait an entire year between star position measurements, though, you will find that your star has come back to the same spot.

Jeff Mangum

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