Monday, 9 May 2016

Transit of Mercury

No birding this weekend, due to a family do-it was in a nice part of the New Forest but I was banned from using bins and the camera. Lots of holiday makers, dog walkers etc so I probably wouldn't have seen much anyway.

I had the day off today as a Mercury transit is taking place. I observed the the 2003 event, and recorded it with the 80mm birding scope, an objective filter and imaged with the Coolpix995. Watched the entire event then, which took place from early morning. The next year I was using a TMB115 apo refractor, a Herschel wedge and the Nikon D1x for solar imaging, and saw the entire Venus transit, initially from home and then from Standalone Farm where we held a public viewing event. A few of my images were published in the British Astronomical Association report, and appeared on a few websites.
Using the refractor was a bit of a bind. Initially I had it mounted on a very sturdy photographic tripod and fluid head. This did work, but was prone to vibration and keeping the sun (or any other target) in view with head was very tricky. I eventually picked up an old Vixen Polaris mount which was put on the tripod and was far better, but the tripod was still an issue. The thing is, I already had a much better mount but had no means of connecting the refractor to it.
Before the TMB was purchased, I had obtained an Intes 8" Maksutov Newtonian and a Losmandy G11 mount. Neither item could be considered portable, but it was possible to break the components down and set up outside. Took a bit of time of course but eventually it got too much and everything ended up in storage for quite a long time.
Some time ago, one of the Letchworth and District AS guys, Tom Moss Davies offered to build me a pier so I could have the mount permanently set up outside. A bit of a dilemma then ensued. The refractor works best with a tall pier, the Newtonian needs one rather lower. I settled on a hight that I thought would work, bought a Losmandy-Vixen dovetail adaptor and Tom set to work and we had it all finished a couple of weeks ago.

This is the set up taken today during the transit. Its rather close to the house, but I can stills see most of the sky and virtually all my observing over the last 35 years has been from this spot.
The transit started just after local noon, and I had about three or four hours until the Sun would be hidden by houses. Hazy cloud was really a problem, though there were a few clearer breaks. The high temperature didn't help much either and as a result, the air was very unsteady.
I tried initially getting some video sequences with a 10mm eyepiece (80X) and the iPhone but had a lot of trouble lining everything up and internal reflections seemed to be a problem, so I concentrated on images with the D3s and a 1.7x converter.

This was soon after first contact and reasonably steady conditions. Its been cropped to show three sunspot groups and the much darker tiny disc of Mercury. BTW north is down and east is left in these images-courtesy of the Herschel wedge.

Cloud was a bit of a problem with the second image, and the air was rather unsteady.

A bit of a close up with Mercury getting closer to the two biggest sunspot groups (both are actually rather small and quiet compared to some we see, but still bigger than Mercury).

The last one I was able to get, and conditions are a lot better. The granulation of the solar 'surface' shows quite well here.
I could have probably got some more images with Mercury near the centre of the solar disc but heat from nearby houses would have been an issue, and thick cloud was starting to build up. The cloud got so bad that the Sun has not been visible since about 4pm-and with about three hours of the transit to go.

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