Nate Holt's Blog

July 5, 2009

Man-made Sun Spots

Filed under: Musings — nateholt @ 9:52 am

(note: originally posted September 2006 on the old blog)

This is pretty cool. This telescopic image of the sun’s disk was reportedly snapped in Normandy by French astro-photographer Thierry Legault.


It shows two man-made (!) “sunspots”, the space shuttle and the International Space Station orbiting the earth together.


So, question is this… how long did Mr. Legault have to snap this picture? Hours, minutes, or seconds? Let’s figure it out.

From grade school, stuff in low-earth orbit takes about 90 minutes to orbit the earth. The sun is 93 million miles away and is about 850,000 miles in diameter. This works out to an apparent width of a half degree or so. That’s all we need. It takes the shuttle 90 minutes to orbit the earth, or go through 360 degrees. It covers the sun for a half degree of that travel (assuming lucky enough to pass right through the center). So, it seems that all we’d have to do is divide 720 into 90 minutes. This would yield about 1/8 minute (7 seconds maximum) that the shuttle is silhouetted against the sun’s disk. Sound about right? Have to be quick to not miss this awesome shot…


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