June 23, 2012

What's Up in July: Planet pairs and meteors follow exciting transit

By BERNIE REIM

The first full month of summer will bring some interesting celestial sights with it, but nothing as dramatic as the transit of Venus we experienced last month.

click image to enlarge

SKY GUIDE: This chart represents the sky as it appears over Maine during July. The stars are shown as they appear at 10:30 p.m. early in the month, at 9:30 p.m. at midmonth and at 8:30 p.m. at month’s end. Saturn and Mars are shown in their midmonth positions. To use the map, hold it vertically and turn it so the direction you are facing is at the bottom.

Sky Chart prepared by George Ayers

Most of Maine got extremely lucky as the skies finally cleared after a solid week of rain just minutes before the great event was due to start. I was well prepared by having a live feed from Mauna Kea in Hawaii projected onto a large screen in York Harbor for a reunion of the class of 1957 from MIT. We also had an 8-inch Dobsonian telescope with solar filters ready to go, though we didn't think we would even use it until a few minutes before the transit started at 6 p.m.

It was interesting to see that the transit started about nine minutes earlier for us in Maine than it did in Hawaii. It was a very dramatic beginning because we were still fighting some clouds as Venus played hide and seek for about half an hour. The clouds racing across the sun added a nice three-dimensional view of the whole scene, giving it more excitement. Then we watched and photographed it through the telescope along with the live feed from Hawaii while we enjoyed a lobster and clambake for the next two hours until the sun set.

I watched the entire event until nearly 1 a.m. from different live feeds across the world. Some of the telescopes had hydrogen alpha filters, so I could also see the red prominences around the sun. There were also about 10 large sunspots on the active sun during this transit, which you can see anytime with just a good solar filter and a pair of binoculars.

Even though we don't need accurate timings of the transit to determine the solar size and distance anymore, there are still many things we can learn today from carefully watching such a rare event. I got a much better sense of the vast size and power of our sun and the great scale of even the inner part of our solar system, which is the smallest part of it.

Venus orbits the sun at 22 miles per second, more than 3 miles per second faster than the Earth moves, and even at that great speed, it still took six and a half hours to complete the transit. Venus was 3 percent of the size of the sun, but it would only be 1 percent of the sun's size if it were the same distance from us. Sometimes called our sister planet, Venus is about the same size as Earth, 8,000 miles in diameter.

I was able to see the black drop effect during both the beginning and ending of this transit, but I did not see the silvery semicircular arc of the heavy atmosphere of Venus starkly outlined against the blackness of space. Fortunately, I saw the silver arc last time, during the end of the transit on the morning of June 8, 2004.

The next transit won't occur until December 2117. However, there will be a less dramatic transit of Mercury on May 9, 2016. These happen 13 times per century.

A really dramatic event that would let you see the entire inner solar system at once is a simultaneous transit of Mercury and Venus. That last happened more than 375,000 years ago and will next happen in the year 69,163.

The most important thing to remember is that you don't need to actually see any of these events for yourself to know about them and their potential to happen. Just like lunar or solar eclipses or northern lights or active meteor showers, these events allow us a brief glimpse of the real inner workings of our solar system. We can't see them all the time because of our very limited Earth-bound perspective.

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