Friday, March 23, 2012

Sun's Dimensions Refined

The image shows the Mercury transit of the sun on Nov. 8, 2006, as seen from the   NASA/ESA Solar and Heliospheric Observatory (SOHO). Image Credit: NASA/ESA/SOHO

A team of scientists from Hawaii, Brazil, and California universities has measured the diameter of the Sun with new accuracy by using the instruments aboard the NASA/ESA Solar and Heliospheric Observatory (SOHO) to time the transits of the planet Mercury across the face of the Sun in 2003 and 2006.

The team is composed of Marcelo Emilio (visiting from Ponta Grossa, Brazil), Jeff Kuhn, and Isabelle Scholl from the University of Hawaii Institute for Astronomy in collaboration with Rock Bush from Stanford University, California. They made the measurements with SOHO's Michelson Doppler Imager (MDI).

The team's results show the Sun's radius to be 432,687 miles (696,342 kilometers) with an uncertainty of only 40 miles (65km). By using the SOHO spacecraft, the team avoided the blurring caused by Earth's atmosphere that occurs when observations are made from the ground.

SOHO has a distinct advantage. Not only does the observatory have an uninterrupted view of our nearest star -- hovering around the Earth-sun Lagrange point 1 (L1), 1.5 million miles from Earth in the direction of the sun -- it doesn't suffer the obscuring effects of the Earth's atmosphere.

The same team is preparing to observe the transit of Venus across the Sun on June 5. They expect these observations will improve on the accuracy of their Mercury-transit observations.

Follow the link below to learn more about SOHO and the recent transits.


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