Wednesday, June 6, 2012

Venus Transit Report

7:17 PM, transit underway, sun going behind the trees.
The transit of Venus early Tuesday evening was the eighth such event since the invention of the telescope. The first in 1631 was predicted, but so far as we know, not successfully viewed by anyone. In 1639 two people saw the black ball of the planet Venus glide slowly across the face of the brilliant sun. About a hundred saw the transits of 1761 and 1769, by which time efforts were being made to time the event and thus determine the scale of the solar system. In 1874 and 1882, when thousands viewed, the United States spent over $300,000 dollars (not adjusting for inflation) on expeditions to time the transit. Though the scale of the solar system has long been fixed by other means, millions saw the transits of 2004 and 2012 live, at least if you count second-hand viewing by means of media. (Sources: Guy Ottewell's Astronomical Calendar for the  numbers of viewers and a lecture by Laurence Marschall for the expenditure.)

Not looking good.
Here at Gettysburg College, about 150 fortunate souls got to see a transit of Venus first hand. For those who organized the event (Jackie Milingo, Dick Cooper, Mike Hayden, and me), disappointing memories of 2004 were fresh. The transit of that year was a morning happening, already in progress at sunrise. A thick fog hung over Gettysburg, and before it burned off, the transit had ended. No one there saw a thing. The transit this Tuesday occurred at the opposite end of the day, beginning just after 6:00 PM and still not halfway over at the time of local sunset. To narrow our chances a bit further, there is a wooded hill to the west of the observatory, and we knew the sun would dip behind those trees well before the official time of sunset. Clouds dogged us through the day. As the staff arrived to set up, the skies turned mostly sunny, only to be followed by a band of thick clouds that closed in around 5:30, just as dozens were arriving at the observatory. Their time on this pale blue dot would be up before the transits of 2117 and 2125, but the only remedy was to put a NASA webcast on a laptop and hope that it would not turn out to be their only view of the event.

Watching the webcast.
As the transit began, the webcast (difficult to see outdoors and frequently buffering) was all we saw. We noticed nothing on the image at first contact, but after several minutes, we could see a tiny dent in the edge of the sun. By 6:30 the whole of the planet Venus was enclosed by the backdrop of the sun, but still only on the webcast. All those outside the observatory were watching a blue patch of sky in the northwest moving excruciatingly slowly toward the sun, and hoping it would get there before the sun went behind the trees. There was no denying that the crowd was getting a bit tense.

"We've got Venus!"
Lines at the scopes.
The wait did pay off. The clouds pulled away from the sun, partially at first. We tweeted "#VenusTransit success @gettysburg!" from @GCPlanetarium at 6:37 when the faculty members supervising the solar-filter equipped scopes got their first glimpses of the sun with the transit in progress. Lines formed behind every active viewing station, but it soon became clear that that sun would remain in the big patch of blue sky until it set, and there would be no hurry. At the peak of activity, people went from view to view, looking in eyepieces or at projections, holding small children up to do the same, and snapping pictures with cameras and cell phones. I took the last picture from the observing platform at 7:17 through the eyepiece of a telescope (see top of post). It shows the sun, partly covered by unfocused leaves, but the spot that is Venus is still visible above them. Then the crowd almost all drifted away and a we started to pack up. A handful of new people walked up, local listeners of WZBT, the college radio station that had promoted the event. I was about tcommiserate with their bad timing when I took a moment to look around and realize the obvious: the athletic practice fields just to our east were still bathed in sunlight. I picked up one of the cased-up Sunspotters and we walked into the sunlit field for their only view, and my last one, of planet Venus against the sun.
Astroscan (red) and projection box.

Cooper with successful video setup.
If you are wondering about the technical side of things. here is what we had set up - all comericially available equipment, some of it quite old. Three 8-inch Schmidt-Cassegrain telescopes (one Celestron and two Meades) with standard solar filters; one Celestron 5 with video eyepiece and monitor; one Edmund Astroscan projecting into a cardboard box (the box shields the faint image); and two Sunspotters, purpose-made solar projection telescopes. As we put it all away, Mike Hayden joked that we should carefully label everything for use in 2117.

7:32 PM, a final look.

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