The plan for tonight is a busy one, a mix of science and engineering observing. I won't have much time for anything other than observing and analysing data tonight, but as usual I did have a few minutes spare to wander outside at sunset in order to harass the tourists.
The shot above shows the UKIRT (right) and Gemini (left) just about at the moment of sunset. The ventilation systems are open on both telescopes, this is to allow warm air trapped inside the dome during the day to be blown away and replaced by cold summit air. This lowers local turbulence and improves the image quality both telescope deliver. You'll note, however, that the shutters pointing at the sun (which is behind my left shoulder in this case) are kept closed. This is to stop sunlight hitting the telescope structure and warming it up. Even a small amount of light can warm a vital part of the telescope (e.g., the secondary mirror). The rise may only be a few tenths of a degree, but it can be enough to degrade the image quality significantly. Once the sun has set these shutters will be opened.
Dozens of orange-clad tourists join me to watch the sun sink below the Pacific Ocean clouds.