Mesopotamians studied astronomy and recorded their theories on clay tablets.
Aristotle said that the Earth was a sphere and we see the moon by the sun"s light. And although it is wrong he thought the Earth was the center of the solar system, and many people believed this for a long time.
In 1543 the book Copernicus wrote about his heliocentric solar system model was published.
Kepler discovered three laws of planetary motion; the area law, the harmonic law, and that the planets have elliptical orbits.
Galileo improved the telescope and also argued against the geocentric model.
Newton made a reflecting telescope, invented calculus, and also studied light. He also made the laws of gravitation and the laws of motion.
Halley was an astronomer who cataloged stars, improved the sextant, and predicted the orbit of a comet that is now named after him.
Einstein came up with the theories of special and general relativity which help explain time and gravity.
Image and Information- https://www.space.com/15524-albert-einstein.html
Hubble is the father of modern cosmology, he found out nebulae were outside of the milky way and that the universe is expanding. After his death, NASA named a space telescope after him.
Hawking studied black holes and theorized that the universe was infinitely large.