What is an Astronomical Unit (AU)?
An astronomical unit (AU) is a measure of distance often used in astronomy, equal to the distance between the Earth and the Sun. In terms of more common units of measurement, an astronomical unit is equal to about 93 million miles (150 million km), or the distance light travels in a little over eight minutes. The symbol AU is most often used to represent the astronomical unit, though less commonly you may see UA used instead. People have been estimating the distance between the Earth and the Sun for quite a long time. Many Greeks came up with measurements, often wrong by fairly enormous margins. The Greek Eusebius came up with a measurement that is surprisingly close to the modern measure of an astronomical unit. In one of his works he estimated it at 804 million stadia. The stadia, a Greek unit of measure, is roughly 605 to 625 feet (85-90m), making his estimate somewhere between 92 and 95 million miles (149-153 million km). At the end of the 17th century, the astronomical unit was of
