How are the number of days in a year related to astronomy?

Related questions

• What's the Earth's "absolute" speed? i.e. in relation to the central Sun, the first-order star,...
• How does density affect earth's layers?
• How fast does the earth rotate? How does this compare to the rotation of other planets?
• At what speed does the earth travel on its orbit around the sun?
• What would happen if the earth's rotation was faster or slower?
• How fast does earth rotate near the equator?
• How fast does the earth rotate per second?
• How fast is the earth traveling along its orbit?
• How fast does the earth rotate on its axis?
• How fast does the earth rotate in one minute? What is the formula to determine this?