Kilometer to Astronomical Unit Converter

A kilometer (km) is a unit of length in the metric system equal to 1,000 meters. It is one of the most commonly used units for measuring medium to long distances on Earth.

The kilometer was first introduced in 1795 during the French Revolution as part of the original metric system. The term comes from the Greek word 'khilioi' meaning 'thousand' and the French word 'mètre'. It became widely adopted throughout Europe in the 19th century and is now the standard unit for road distances in most countries worldwide.

Kilometers are extensively used for measuring road distances, city planning, geographical surveys, and athletic events like marathons. Most countries use kilometers for speed limits (km/h) and fuel efficiency measurements. It's the standard unit for mapping and GPS navigation systems globally.

An astronomical unit (AU) is a unit of length approximately equal to the average distance from Earth to the Sun, defined as exactly 149,597,870.7 kilometers or about 93 million miles.

The astronomical unit was originally defined as the semi-major axis of Earth's orbit around the Sun. It was first estimated by Giovanni Cassini in 1672 and has been refined over centuries. In 2012, the International Astronomical Union redefined it as an exact value rather than a measured quantity.

Astronomical units are primarily used for measuring distances within the solar system, including distances between planets, asteroids, and comets. They're standard in planetary science, space mission planning, and solar system astronomy.