What is Astronomy?
Astronomy is study of universe.
Although ancient cultures did not fully understand how the planets, moons, and stars move in relation to each other, their observations led to the first calendars.
Our Modern Calendar
The years, months, and days of our modern calendar are based on the observation of bodies in our solar system. A year is the time required for the Earth to orbit once around the sun. A month is roughly the amount of time required for the moon to orbit once around the Earth. (The wordmonth comes from the word moon.) A day is the time required for the Earth to rotate once on its axis.