Thursday, 7 June 2012
An event equally momentous to the Queens Diamond Jubilee, the transit of Venus grabbed my attention.
Britain’s location and the threat of clouds meant that I was unlikely to see the last few minutes of the transit of venus at 5am or so on the 6th of June. However, having a long standing interest in solar activity via the SOHO and SDO solar observation satellites, I thought these would present a good opportunity to watch the transit from space.
Surprisingly, the older SOHO satellite, although placed at the L1 Lagrange point directly between the Sun and Earth, would not see Venus transit across the sun. The reason being that the SOHO satellite is placed about 1.5 million kilometres closer to the sun and the angle of view is sufficiently different.
Fortunately, the SDO satellite is in a geosynchronous orbit around the Earth, a mere 36,000 kilometers above the Pacific Ocean just off the coasts of Peru and Mexico. It was expected to see the transit much as we would from Earth. The SDO also had a special Venus transit page at http://venustransit.gsfc.nasa.gov/data and therefore was worth watching.
There were two other opportunities to view the event live over the internet. NASA Edge promised to bring a live stream from the telescopes on the peaks of Mona Loa in Hawaii at http://www.ustream.tv/nasaedge. Across the Pacific, the University of Quennsland was also coordinating live coverage from Australian telescopes – at http://www.uq.edu.au/transit-of-venus/.
The transit was supposed to start with first contact with the disc of the sun (as seen from Earth) at 23:16 BST from Australia and about 23:09 from Mona Loa in Hawaii.
I had all three sites up and by 22:25 BST. Venus could be seen approaching the sun via through the SDO when viewed using very short ultraviolet light. These wavelengths shows the corona or outer atmosphere of the sun and are not as bright as the photosphere - the bright yellow sun surface we usually see. Flicking between channels, the Mona Loa broadcast started at 10:45 and the Australians also went live.
Just before first contact, when Venus just appears to touch the edge of the sun, the Hawaiian telescope went off line briefly! Having access to several different observation sites paid off. I observed first contact via the SDO at about 23:07:45 BST, followed later by the Australian telescopes. Eventually, the Americans did come back online.
You can see the images I downloaded at the time from the SDO page, every couple of minutes or so.
They show Venus and the sun's edge highly magnified as the planet approaches and then begins to move across the sun. These are followed by pictures of the entire sun about halfway through the transit.
I deliberately downloaded images on the 6th (the following day) to show Venus against the sun as seen at different wavelengths.Each successive image looks deeper into the sun. We start at the Corona, where flares are visible and move into the chromosphere, where you can see convection cells. Then we reach the low temperature, quiet zone of the sun. Finally, we arrive at the final layer which is the one we usually see with our naked (but protected!) eyes, the photosphere.
A particular lovely feature is that Venus crosses the sun close to a region of sunspots and high solar activity. We are currently in the peak period of the sun's activity in its 11 year cycle and sunspots are a regular feature on the sun's surface.
The next transit of Venus across the sun is expected on the 10th December, 2117 so I was very happy to have lived at the right time in our history to see this momentous event.
Viewing the transit of Venus would not have been possible in this way if information from NASA, the SDO, the University of Queensland and access to the internet were not made publicly available. This event demonstrated to me, why open access to technology and information is important.
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