The Hindu cosmological time cycles explained in the Surya Siddhanta, give the average length of the sidereal year (the length of the Earth's revolution around the Sun) as 365.2563627 days, which is only 1.4 seconds longer than the modern value of 365.256363004 days. His views go unquestioned for nearly 1500 years in Europe and are passed down to Arabic and medieval European astronomers in his book the Almagest.He also proposed astronomical calculation of the sidereal revolution of planets. Ptolemy publishes his star catalogue, listing 48 constellations and endorses the geocentric (Earth-centered) view of the universe. The astronomer Shi Shen is believed to have cataloged 809 stars in 122 constellations, and he also made the earliest known observation of sunspots. Vitruvius explains that an object’s fall speed depends on their specific gravity. Their records of the comet's movement allow astronomers today to predict accurately how the comet's orbit changes over the centuries. The earliest recorded sighting of Halley's Comet is made by Chinese astronomers. However, there were only a few people who took the theory seriously. His heliocentric model places the Sun at its center, with Earth as just one planet orbiting it. 270 BCE Īristarchus of Samos proposes heliocentrism as an alternative to the Earth-centered universe. It promotes the idea that everything in the universe moves in harmony and that the Sun, Moon, and planets move around Earth in perfect circles.Īristotle, a Greek polymath, described gravity as a downward motion which moves towards the centre of the earth. Plato, a Greek philosopher, founds a school (the Platonic Academy) that will influence the next 2000 years. 400 BCE Īround this date, Babylonians use the zodiac to divide the heavens into twelve equal segments of thirty degrees each, the better to record and communicate information about the position of celestial bodies.

He was the first to explain that the Moon shines due to reflected light from the Sun. Thales of Miletus is said to have predicted a solar eclipse.Īnaxagoras produced a correct explanation for eclipses and then described the Sun as a fiery mass larger than the Peloponnese, as well as attempting to explain rainbows and meteors.

In 6th century BCE Greece, this knowledge is used to predict eclipses. From this they created the first almanacs – tables of the movements of the Sun, Moon, and planets for the use in astrology. Mayan astronomers discover an 18.7-year cycle in the rising and setting of the Moon. List of important events in the history of astronomy

Astrometry for astrophysics pdf