The field of study of the universe is called astronomy. The universe is commonly defined as the totality of everything that exists or is known to exist. It consists of galaxies, planets, stars, meteorites, satellites and all other forms of matter and energy. The spatial size of the entire universe is still unknown, but it is possible to measure the observable universe.
1. The Geocentric Theory
The Sun, Moon and stars appear to rise in the East and move towards the West, as if going around the Earth. Objects that do not twinkle and drift against the backdrop of stars are the planets.
Two motions of the Moon
- Daily motion: the Moon rises in the east and sets in the west, as if it goes around the Earth in one day.
- Motion against the stars: if the Moon is near the star Asvini today, it is near Bharani (east of Asvini) tomorrow and near Kartikai the next day. Moving little by little eastwards, it returns near Asvini after 27 days – a circle from west to east in about 27 days.
- Astronomers like Aryabhata said that the Earth is spinning on its axis, which causes the apparent daily motion from East to West.