Greece is known for some of the most famous and important ancient astronomers ever. Ptolemy, Thales, Aristarchus, and Hipparchus are among the men who, alone, changed the idea of astronomy and had many revolutionary discoveries about the universe. Here is a small description of each of them, the discoveries they had, and the impact they've left on today.
Ptolemy lived from 89 A.D. to 168 A.D. and had many discoveries about the Earth and the other planets. For instance, he found out that earth had a spherical shape, which back then most people thought it to be flat. He knew this because he was able to notice that people who lived farther east saw the sun rise earlier than people living to the west. Ptolemy was also the first person to propose the famous theory of epicycles, where the Sun, Moon, and other planets orbit in circles, but also rotate in a smaller a circle within the large cycle. He named and charted forty-eight of the eighty-eight constellations that we know of today. Ptolemy was very well known throughout Greece and is often considered today to be one of the best and most influential astronomers.
Thales, who lived at the beginning of the sixth century B.C., was one of the original Greek astronomers and is credited for several inventions. He was the the founder of trigonometry, which is a branch of mathematics dealing with measuring the angles of triangles. Trigonometry is occasionally used by astronomers to map stars and planets. Thales also had many discoveries including recognizing that the Ursa Minor constellation was crucial for sailors to navigate as well as measuring the diameter of the Sun. These two things were great leaps forward in astronomy and they inspired later astronomers to continue observing the Sun and the constellations. He is also credited for successfully predicting an eclipse in 585 B.C.
Hipparchus is often called one of the greatest astronomers ever for the many advancements and discoveries he had in the field of astronomy. He was a Greek astronomer that lived from 189 B.C. to 120 B.C. and compiled some of the best known records in Greece. He was one of the first astronomers to keep long-term notes of observations. and this allowed him to discover several things. For example, he was able to use these records to find the exact length of a year, recognize that the seasons are not completely equal in length, and successfully predict eclipses. Hipparchus was also the first to make a large catalog of stars. This catalog consisted of 850 of the brightest stars that he observed and that can be seen by the naked eye. He rated each star on a scale of 1 to 6, with 1 being the brightest and 6 being the faintest. This record of stars was crucial to several of his other discoveries, and it has led to many findings made by later astronomers.
Aristarchus was a Greek astronomer that is known for his many findings involving the universe. One of his first discoveries was that the apparent angular sizes of the Moon and the Sun are the same, which is why their sizes are in proportion to their distances from the Earth. He also recognized that when there is a half moon, the Sun-Moon-Earth angle is exactly a right angle. This allowed him to determine that the distance from the Earth to the Sun was twenty times the distance from the Earth to the Moon. Aristarchus recorded the eclipse time and the lunar orbital period as well, which allowed him to discover that the Moon is one third the size of the Earth, and that the Sun is seven times the Earth. This also allowed him to calculate he distances from the Sun to the Earth and from the Moon to the Earth relative to the diameter of the Earth. Finally, Aristarchus was the first Greek astronomer to propose the heliocentric theory, where the Earth orbits around the Sun.