Astronomy is a subject taught at Hogwarts School of Witchcraft and Wizardry. It is a required subject for first through fifth years; it can be dropped in the sixth year. It is taught by Professor Aurora Sinistra.
Astronomy is also the only field of study at Hogwarts which has a direct equivalent in the Muggle world. Known student activities include learning the names of stars, constellations and planets, as well as their location and movements, and describing the environments of planets and moons.
Astronomy classes take place in the Astronomy Tower, the tallest tower in Hogwarts Castle, and include sky observation sessions with telescopes (each student has to buy one of his/her own).
Harry only received an Acceptable on his O.W.L. exam in Astronomy because at the same time it was being given late at night, Umbridge tried to have Hagrid arrested. There was a protracted fight on the grounds below the tower which totally distracted Harry and everybody else.