I think I've pretty much finished recycling and reprocessing the photos I took before the great computer crash of April 2009, at least those taken at the summit of Mauna Kea. There may be two or three more I post soon but that's it until I'm back up there, although I have a very busy summit schedule in August, so should get some opportunities! There are plenty of others I need to work on that were taken in Hilo and the Puna district of the Big Island but they can wait awhile.
This picture is of the twin Kecks on the summit. On this particular evening the domes would remain closed for quite some time after sunset due to clouds at summit level. The last thing you need is to have water condense on any of the optics, such as the telescope mirrors themselves, and then possibly freeze as the temperatures drop at night. That once happened to me on an observing run in Australia and both the observing team and telescope operator were rather embarrassed! Fortunately, it was alright in the end as we managed to evaporate the water before it could cause any problems.
The Kecks are among the largest optical (and infrared) telescopes on the planet and certainly the largest established optical telescopes with primary mirrors 10-metres in diameter (approximately 33-feet). The primary mirrors aren't one single piece of glass, in fact they are essentially a honeycomb of smaller one metre diameter hexagonal mirrors. It is extremely challenging to build a single-piece large astronomical mirror although the technology is certainly improving (the precision needed in the final mirror is extraordinary). 8-metre single mirror optical telescopes do exist (Gemini on Mauna Kea is an example) and I'm sure one day there will be larger ones although how you transport such large mirrors might be a bit of an issue, especially on the narrow dirt road on Mauna Kea. Single mirrors are definitely an advantage for infrared observing as the emissivity is reduced, i.e., the glow from the telescope itself is minimised. A honeycomb type design does tend to have emissive regions in between the mirror segments although as always there are clever ways to reduce that.
On evenings like those pictured above, so typical during the winter and spring, we'll arrive at the summit with clouds surrounding us. Inexperienced visitors tend to be concerned, especially during the foggy drive up, that we won't be observing that night, but nearly always, just as the sun sets, the clouds will drop way below the summit and it will be safe to open the domes. On some occasions that doesn't happen of course, but when you've worked here for several years you often just have a "feel" for what the clouds will do and can reassure the visiting astronomers that they'll soon be able to take some data!
PS. Incidentally, especially for my Europe- and Asia-based readers, the region-free PAL release of "Hawaiian Starlight" is now available. If for some reason you like my pictures taken at the summit of Mauna Kea I think you'll love the DVD. Beautiful and stunning movies of the summit, telescopes, sunsets/sunrises and the universe accompanied by some great music and no narration, it's just a visual and aural spectacular. Make sure the volume is turned up!