solar parallax

astronomy

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July 14, 2026

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Solar parallax is a fundamental concept in astronomy used to determine the distance of the Sun from Earth. It is defined as the angle subtended at the Sun by the semidiameter of Earth, with an adopted value of 8.80 arcseconds. This measurement is crucial for establishing the dimensions of the solar system.12

The principle behind measuring solar parallax is similar to how our two eyes allow us to perceive depth. By observing the Sun from two different points, such as Earth at opposite ends of its orbit, astronomers can measure the apparent shift in the Sun's position against more distant background stars. This shift, known as parallax, forms a triangle with the two observation points and the Sun. Knowing the base of this triangle (Earth's orbital diameter) and measuring the parallax angle allows for the calculation of the distance to the Sun. This distance is also known as the astronomical unit.23

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parallax
Solar parallax
The basic method used for determining solar parallax is the determination of trigonometric parallax. In accordance with the law of gravitation, the relative distances of the planets from the Sun are known, and the distance of the Sun from Earth can be taken…
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The basic method used for determining solar parallax is the determination of trigonometric parallax. In accordance with the law of gravitation, the relative distances of the planets from the Sun are known, and the distance of the Sun from Earth can be taken…
Read More

Sir Harold Spencer Jones
…astronomy and in particular the solar parallax—the angle subtended by the Earth’s radius as viewed from the Sun. Using information from observations of the asteroid Eros during its close approach to the Earth in 1931, he computed in 1941 the solar parallax and from that the mean distance to the…
Read More
…astronomy and in particular the solar parallax—the angle subtended by the Earth’s radius as viewed from the Sun. Using information from observations of the asteroid Eros during its close approach to the Earth in 1931, he computed in 1941 the solar parallax and from that the mean distance to the…
Read More