Eratosthenes276 BC - 194 BC
He was the first one to accurately measure the circumference of the earth which has led to use even today using better methods that were bounced off that idea he had
Claudius Ptolemy100 AD
he created models to predict future motion of planets or even past motion of planets which we still do today
Nicolaus Copernicus1473 - 1543
He was the first person to completely model the solar system with the idea that the sun was at the center of the solar system instead of earth. this led to many more discoveries which made more sense because the sun is actually at the center.
Tycho Brahe1546 - 1601
Known for an insanely accurate depiction of the solar system for the time period he lived in. this led to many more discoveries about the solar system because he created an actually accurate depiction. (i picked a random date(within his life) that made semi-sense because I don't know exactly when he discovered it)
Johannes Kepler1571 - 1630
He is well known for his laws of planetary motion which we still use today to determine the motion of planets
Sir Isaac Newton1643 - 1727
He discovered gravity which has been one of the most helpful things to astronomy to this day
Albert Einstein1879 - 1955
He is extremely famous for his equation E = mc^2. This and his theory of relativity has helped science so much in the past almost 100 years.