The ISS Transit and Sunspot Group AR 1057

July 11, 2010

ISSsolar transit

Photographers: Peter Stetson and John Stetson
Summary Authors: Peter Stetson and John Stetson

The photo above shows the International Space Station (ISS) transiting the Sun on March 25, 2010 as observed from Kettle Cove State Park, Cape Elizabeth, Maine. We set up two telescopes, a four and a five inch (10 and 12 cm) refractor, to image the 0.62 second transiting the Sun. This is the first time that we've been able to capture the ISS and such a well defined active solar region coincidentally. In this case the sunspots, in AR 1057, and ISS are in the same frame. We used the arc of the limb of the Sun to determine the size of the active sunspot region. Because we knew that the ISS is nearly 37 arc seconds across, we could use the ISS to give us an approximation of the size of the sunspots. Our Sun's average size is 32 arc minutes: 32 arc minutes times 60 equals 1920 arc seconds; 1920 divided by 37 arc seconds equals 51.89. These sunspots are huge; approximately the length of four Earths.