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What is the astronomical unit

Astronomical unit

The astronomical unit is the distance between the Sun and the Earth. It is also used as a unit to measure distances in the solar system. The average distance between the Sun and Earth is about 149.6 million kilometers or 92.96 million miles.


The distance between the Sun and the Earth is a discretionary process because the Earth’s orbit around the Sun is elliptical. a distance between the sun and Earth in early January, Astronomical unit to estimate the distance between the sun and the planets are used when the size of the planet is negligible for the size of the sun planet, in addition to not change the distance between them throughout the year.

Date of estimation

The Greek astronomer Aristarchus was the first to attempt to estimate the distance between the Sun and the Earth in 250 BC, and then Christiaan Huygens attempted to estimate the distance between the Sun and the Earth in 1653, where he made his estimates through Venus, which helped him to reach the idea that When half of Venus is illuminated by sunlight, a right-angled triangle is formed with three heads: the Sun, Venus, and Earth. You are not a prosecutor Scientific evidence, so they weren’t very accurate.

The researcher Giovanni Cassini conducted research in 1672 based on the principle of angular difference or difference of view with different angle of view (in English: Parallax), which forms a celestial triangle from the Earth, the sun, and another third planet, where the angle of light from the third planet was determined On Earth, Giovanni was able to find out the distance between Mars and Earth, and then discovered the distance between the Sun and Earth.

Modern methods of measuring the astronomical unit

In 1976, the International Astronomical Union (IAU) defined an astronomical unit is a distance between the Sun and the infinite particles, which orbits in a circular orbit for a year. This definition is based on the mass of the Sun, which decreases permanently, thus changing the astronomical unit continuously and does not remain constant.


Several modern and direct methods have been found to measure the distance between the Sun and the Earth, using advanced technology, radar, and advanced spacecraft. In August 2012, the distance between the Earth and the Sun was determined to be 149,597,870,700 km.

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