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Wednesday 27 June 2012

Photographing the Venus transit

Last week, we explained why scientists are still interested in the Venus transit of the Sun, which featured this stunning photo taken by astronomer and TWDK contributor Nick Howes.
Photograph of the Sun using H-Alpha and CaK filters
© All rights reserved by Nick Howes, image reproduced with permission.

As promised, Nick explains how he did it in our first ever guest post.
“You do know about Spacefest?” was the email from UN Space Generation's Jane Macarthur, when I casually mentioned that I planned to be in Tucson for the transit of Venus. This event, now in its 4th year held at the Marriott hotel, plays host to some really special names in the world of space flight, but this year, with the 40th anniversary of the last Apollo flight, all the stops had been pulled out and no less than 10 astronauts to have walked on or flown to the Moon/on Apollo missions were in attendance. Meeting up with a plethora of the world's greatest names in astronomy and research was something I will never ever forget.

The transit itself was set to start at around 3pm local time in Tucson. I’d been kindly invited to the home of Geoff Notkin, star of Science Channel/Discovery Channel’s “Meteorite Men”, a multi award winning program which features Geoff and his colleague Steve Arnold, visiting the world’s great meteorite sites in search of new and exciting discoveries. Geoff’s home, fondly known as “The Bat Cave” is the HQ of the Meteorite Men, where Geoff and his amazing team of assistants work.

I arrived about lunch time, with two telescopes in hand. I’d brought from the UK a 66mm Calcium K line (CaK) telescope, which uses a special filter to isolate the frequency of light which is absorbed by Calcium, which is one where some of the Sun's more interesting features can be observed. It knocks out around 99.8% of all the harmful radiation coming from the Sun using a combination of filters, making it safe to look at an image with. However, as it's in to the UV portion of the spectrum, the view is at best very dim to most people's eyes. Alongside this, I’d brought a Solarscope SV50 Hydrogen-alpha telescope which looks at a frequency associated with ionized hydrogen (which makes up three quarters of the Sun).

My telescope mount allowed me to track the Sun effortlessly, and after setting up the mount and telescopes out on the front patio of Geoff’s house, I trailed the associated cables into the living room area, where we comfortably could adjust the scope through a window, avoiding the summer heat outside. I’d coated the telescopes in aluminium foil to help keep them cool, and then using a combination of two cameras, started the imaging run about 10 minutes before the predicted first contact, which occurred just after 3.05PM local time in the H-Alpha images.

Then for the next 4 hours, I switched between taking images of the full disc of the Sun in both H-Alpha and CaK imaging, intermingled with some “off band” white light imaging using the SV50, and then adding a lens to give very detailed looks at the active regions which littered the Sun. The CaK view in particular was stunning, with a huge active region clearly visible.

We had absolutely no clouds for the entire 4 hours, in fact, it was some of the bluest sky I had ever seen. The thermals did have a part to play in the images, but working at around 10-12 frames/second, I managed to get more than enough image data to “beat the seeing” (close to 400GB in total).

Despite not seeing the entire event from Tucson, the over 4 hours of amazing skies more than made up for losing the last part at sunset. At the end of the event, we had some celebratory cocktails, and Geoff took a group of us out for a fantastic meal. All in all, a day I’ll never forget.

For those interested in the specifics, the equipment Nick was using is as follows:
  • Compact EQ3-Pro synscan mount
  • Custom made Calcium filter at 2.3A
  • Solarscope SV50
  • Two Lumenera Skynyx 2-1 and 2-2 cameras
  • 2.5X Televue powermates
If you'd like to see more of his work, why not check out Nick's photostream on Flickr. Be warned though, it'll take you a long time to see them all - he has hundreds!

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