You may notice that when you are stargazing in your yard at 10:00 every night, the stars appear slightly to the west of where they were the night before.
Stars rise 4 minutes earlier every night, and set 4 minutes earlier.
Therefore, over the months, the starry night changes.
Over the period of a year, those minutes add up to 24 hours, so that every 12 months, the same stars show up at the same positions in the sky.
The difference in the stars’ rising and setting times results from Earth’s rotation around the Sun.
The celestial sphere remains relatively still, but Earth moves around the Sun.
The stars appear to be in a different place at the same time each night because, in fact, you are in a different place in space every night.
Because it takes 365 days for Earth to rotate around the Sun, you have 365 slightly different night skies to study.
