Millimeter to Astronomical Unit Converter

A millimeter (mm) is a unit of length in the metric system equal to one-thousandth of a meter (0.001 m). It is used for precise measurements of small objects and dimensions.

The millimeter emerged from the metric system's decimal structure, with the prefix 'milli-' from the Latin word 'mille' meaning 'thousand'. It became essential as precision manufacturing and engineering developed during the Industrial Revolution.

Millimeters are crucial in engineering, manufacturing, medicine, and precision work. They're used for measuring thickness of materials, mechanical tolerances, medical instruments, jewelry, and in technical drawings. Most precision tools and calipers use millimeter measurements.

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.