Astronomical study is the scientific study of celestial objects, such as stars, planets, comets, and galaxies. Tides, which are the periodic rise and fall of the sea level, are studied in relation to the gravitational pull of the moon and sun. GALAXY is a term used to describe a large group of stars, gas, and dust held together by gravity. Astronomical study can involve observing and analyzing these objects to gain a better understanding of their properties and behavior.