Solar radius

Solar radius is a unit of distance used to express the size of stars in astronomy equal to radius of the Sun. The solar radius is usually defined as the radius to the layer in the solar photosphere where the optical depth equals 2/3.:

The solar radius is approximately 695,700 kilometres (432,288 miles), which is about 10 times the average radius of Jupiter, 110 times the radius of the Earth, and 1/215th of an astronomical unit, the distance of Earth from the Sun. It varies slightly from pole to equator due to its rotation, which induces an oblateness of order 10 parts per million. (See 1 gigametre for similar distances.)

The SOHO spacecraft was used to measure the radius of the Sun by timing transits of Mercury across the surface during 2003 and 2006. The result was a measured radius of 696,342 ± 65 kilometres (432,687 ± 40 miles).

Haberreiter, Schmutz & Kosovichev (2008) determined the radius corresponding to the solar photosphere to be 695,660 ± 140 kilometres (432,263 ± 87 miles). This new value is consistent with helioseismic estimates, and the same study showed that previous estimates using inflection point methods had been overestimated by approximately 300 km.