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2012 Venus Transit
On June 5, 2012 Venus transited the Sun starting at about 2209 UTC (5:09 p.m. CDT) and lasted for about six hours. Cathy and I were able to watch it until 0059 UTC on June 6, 2012 (7:59 p.m. CDT, June 5, 2012), when the Sun set at our location. Transits happen when a planet crosses between Earth and the Sun. Only Mercury and Venus, which are closer to the Sun than our planet, can undergo this unusual alignment. When Venus passes directly between earth and the Sun, we see the distant planet as a small dot gliding slowly across the face of the Sun. Historically, this rare alignment is how we measured the size of our solar system. With its relatively tight orbit, Mercury circles the Sun fast enough that we see the innermost planet transit every 13 to 14 years. But transits of Venus are exceedingly rare, due to that world's tilted orbit. After this 2012 Venus transit, we won't see another until 2117.
Transits of Venus are so rare because the planet's orbit is tilted just over three degrees from the plane of the solar system. This means that most of the time Venus passes above or below the Sun's disk, as seen from Earth. On average, we see four transits of Venus within 243 years. The events happen in pairs spaced eight years apart, and they alternate whether Venus crosses the top or the bottom of the solar disk. This year, for instance, the planet transited the top of the Sun.
Observations from different locations on Earth allowed scientists to not only triangulate the true size of the Sun but also to more accurately determine the distance between the Sun and Earth. The transit, meanwhile, allowed astronomers to get a broader picture of Venuvian weather in the planet's upper atmosphere and see how different regions interact. Watching how the Sun's light changes during the Venus transit can show astronomers whether their calculations capture the known properties of a nearby planet, helping them to refine their models for studying more distant worlds.
Below are a couple of photos of Venus transiting the Sun on Tuesday, June 5, 2012. The top photo is in Hydrogen Alpha (HA) and the second photo used a White Solar Filter.
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