As its name suggests, an astronomical unit is a unit of measurement for calculating distances in the universe. It normally appears in its abbreviated form (ua) and the International Astronomical Union defines it as “the distance from the center of the Sun to a particle of small mass that, following a circular orbit, had a translation period of 365.2568983 days. 1 AU is exactly 149,597,870.691 kilometers. ”In other words, 1 AU is the same as 150 million kilometers, slightly less than the distance from the Sun to the Earth.
The need to create this gigantic measure arose in the 16th-17th centuries, when the distances that separated the different bodies of the Solar System and the Universe were not precisely known. Copernicus himself used trigonometry to calculate the distances between the planets that were known until then, based on the distance between the Earth and the Sun.
Later many other astronomers verified these calculations and observed that the father of the heliocentric theory was not badly misguided. While Copernicus calculated that the distance to the Sun from Mercury was 0.386 ua , the real one is 0.389 ua; Likewise, the distance between Saturn and the Sun is not 9,174 as Copernicus claimed, but 9,555 ua.
Later, when the speed of light was known exactly, more specific and equally useful conversions were made for astronomers . For example, 1 u is 499.0047838362 light seconds (the distance light travels in vacuum in one second).
