Sun, 1. July 2012
Astro-Speaker Watch - May 2012
Fred Watson and the MAS Transit Event
Professor Fred Watson is always a very entertaining speaker, easily comprehended by all who are present. He has visited MAS numerous times and last month's talk, entitled "In the Face of The Sun", was a lively romp through the upcoming transit of Venus, also touching on exo-planets, eclipses and aurorae.
Fred explained that transits occur in repeating patterns every 243 years when the orbital planes of Venus and Earth coincide. During this period, only four transits occur, in two pairs. The first pair comes in December and the second in June. There were no transits of Venus during the twentieth century and the first of the current transit pair came eight years ago.
The 1631 and 1639 transits were believed to be the first ever observed (following the invention of the telescope) and Fred took us through the scientific opportunity that the earliest transits gave astronomers to accurately establish the scale of the Solar System, using the parallax method from data gathered from varying global observation sites. The first scientific observations were of the 1639 event, predicted by Jeremiah Horrocks and the first transit photographs were taken in 1882, making this year's transit only the third to be photographed and only the eighth to be observed visually.
Fred told us that transits were currently being used to discover exo-planets around other stars, and he also talked about the aurorae, inviting anyone interested to join him on a tour of Sweden, Norway and Iceland, in pursuit of the Northern Lights, next January.
He also talked about the coincidence that both the Moon and the Sun appear the same size to us, suggesting that this may perhaps be a contributing factor in the evolution of mankind. He advised that eventually the Moon's orbit will have receded so that we only see annular solar eclipses, rather than total eclipses. Coincidentally, the day after Fred's talk, I read an article published at http://astrobob.areavoices.com/2012/05/20/561667292-a-d-date-of-earths-last-solar-eclipse/ which predicted that the last ever total solar eclipse would occur in approximately the year 561,667,292 A.D.
As usual our members came up with a series of great questions but Fred was stumped by ex-President Noel Sharpe's incisive question about whether the early transit observers used protection!
Another good question which Fred was unable to provide a definitive answer to was whether transits of Venus and Mercury could occur together. To that, I now refer you to the following Wikipedia page http://en.wikipedia.org/wiki/Transit_of_Mercury which predicts that the last simultaneous occurrence of Mercury and Venus transits occurred in the year 373,173 BCE and the next will not occur until the year 69,163 CE, 'closely followed' by another in 224,508 CE. Wouldn't that be a sight?
So how did Transit Day work out for MAS?
We obtained very late approval to set up our solar telescopes at Eagle Vale Leisure Centre and we are very grateful to the Centre Management and to Campbelltown City Council for allowing us to do that. However, we were unable to promote the event as much as we would have liked.
The weather outlook leading up to the event was very poor and I awoke that morning with that awful sinking feeling you always get when you realise that things are not going to plan. Thick clouds! It was obvious that it would not be a good day for astronomy. However, as it was (almost) a unique event in our lives, seven of our members still turned up and we had four solar telescopes on duty with one more in reserve.
The poor visual conditions persisted throughout the transit but we had some occasional short breaks in the clouds to observe it. We were able to show it to everyone who had the patience to wait for a glimpse. Some of the patrons came to the telescopes dripping wet, straight out of the pool! Many were amazed to see how tiny Venus is, compared to the size of the Sun and we were asked a lot of questions about the Solar System.
It worked out well, under the circumstances, although 95% of the period was spent looking at clouds.
The next big astro-event locally will be a partial eclipse of the Sun in November (total eclipse in North Queensland).
(This article first appeared in the June edition of Prime Focus magazine, the monthly Journal of Macarthur Astronomical Society.)
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