Learn the basics of astronomy with historical background and an introduction to the basic astronomy concepts, details about planets, satellites, asteroids, comets and meteors. Also learn the history of Astronomy from its origins in the religious, mythological, and astrological practices of prehistory through to modern astronomy.
In 1609, a German mathematician by the name of Johannes Kepler discovered a simple relationship between the distance from the Sun and a planet's orbital period. This relationship became the foundation for Kepler's laws of planetary motion.
How far away is the Moon? Hipparchus first calculated the distance in 190BC using a simple method involving trigonometry and was accurate to 1,000km!
How large is the Earth, and how do we know that? It was the Greek mathematician and astronomer Eratosthenes who first calculated the size of the Earth, and he did it in 200 BC with a stick!
The IAU system of constants defines a system of astronomical units for length, mass and time, and also includes astronomical constants such as the speed of light and the constant of gravitation which allow transformations between astronomical units and SI units.