A group of scientists from Hawaii, Brazil and California has measured the diameter of the Sun with unprecedented accuracy by using a spacecraft to time the transits of the planet Mercury across the face of the Sun in 2003 and 2006.

They measured the Sun's radius as 696,342 km (432,687 miles) with an uncertainty of only 65 km. This was achieved by using the solar telescope aboard a NASA satellite, thereby bypassing the blurring caused by Earth's atmosphere that occurs when observations are made from the ground, notes a University of Hawaii Institute for Astronomy Press Release.

The measurements of the Sun's size were made by University of Hawaii Institute for Astronomy scientists. They used the Michelson Doppler Imager (MDI) aboard NASA's Solar and Heliospheric Observatory (SOHO) to make the measurements.

Transits of Mercury occur 12-13 times per century, so observations like this allow us to refine our understanding of the Sun's inner structure. The team is preparing to observe the transit of Venus across the Sun on June 5. They expect these observations will improve the accuracy of their solar size measurement even further.