Sun’s Diameter Measured With Unprecedented Accuracy

Mercury’s path across the solar disk as seen from SOHO on November 8, 2006 (image from NASA)

A group of scientists from Hawaiʻi, 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. Their scientific paper has been accepted by the Astrophysical Journal.

The measurements of the Sun’s size were made by University of Hawaiʻi at Mānoa Institute for Astronomy scientists Marcelo Emilio (visiting from Ponta Grossa, Brazil), Jeffrey Kuhn and Isabelle Scholl in collaboration with Rock Bush of Stanford University. They used the Michelson Doppler Imager aboard NASA’s Solar and Heliospheric Observatory to make the measurements.

They measured the Sun’s radius as 696,342 km (432,687 miles) with an uncertainty of only 65 km (40 miles). 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.

“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, and the connections between the Sun’s output and Earth’s climate,” said Kuhn.

The team is preparing to observe the transit of Venus across the Sun on June 5, 2012. They expect these observations will improve the accuracy of their solar size measurement even further.

Read the news release for more.

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