An ocean of clouds

Hualalai surrounded by a sea of clouds at sunset.

Preparing for the night

Many of the observatories on Mauna Kea open their domes before the sun has set. It's not because they're observing anything, it's to help equalize the temperature within the dome to that of the outside air. Having said that, many observatories can observe during the day, especially those that operate in the mid-infrared (beyond about a wavelength of 2.5 microns) and the submillimetre (such as the JCMT and CSO). Many years ago we started the commissioning process of an instrument called Michelle by observing after the night shift had ended until around nine or ten in the morning. After that the sun is high in the sky and the risk of the primary mirror concentrating sunlight on part of the dome becomes a real risk. Even before then we would regularly go out into the dome to make sure we weren't setting fire to the observatory!

Those were long and tiring shifts, I remember them well.

During the day heat builds up inside the domes. Some observatories actively control the dome temperature via air conditioning whereas we (UKIRT) control the primary mirror temperature to keep it as cold as the expected night-time air. This is a project we've been doing for a couple of years now and it's made a significant improvement to the delivered image quality in the first few hours of the night.

No matter how these things are handled though, it's always best to try and ventilate the dome for as long as you can before observing starts as any difference in the temperatures inside the dome and the outside air result in local turbulence and reduced image quality. Gemini, one of the observatories that employs active cooling of the dome, will still open the vents early when they can, as seen above. I think the only issue I'd have with this is that sunlight is apparently being allowed to strike the telescope structure directly. Our own experience with this is that it's enough to heat the structure so that thermal expansion occurs. It's only a few microns but it makes a difference. On the other hand, Gemini is a much larger telescope and therefore has a much larger thermal mass than us, so it may not be a problem.

At UKIRT we open the dome ventilation system as soon as the night crew are at the summit although the vents facing the setting sun remain closed. The dome slit is opened as well to help with the cooling process although we make sure the slit is facing away from the sun! We rely on the summit winds to blow through the dome and equalize the temperatures although that's a bit of a problem when it's calm. Fortunately, that's doesn't happen very often.

This is also the time that the summit tourists find their best spots to view the western sky for a sunset of a lifetime. I tend to join them when I'm on the summit because no matter how many times I've watched a Mauna Kea sunset, they simply never become boring.

Sunset tourists

The sun has just disappeared below the horizon and all around me people have witnessed a sight they'll probably only see once in a lifetime. You might think those of us that work on Mauna Kea's summit would be bored of the sight by now, but that isn't the case. If you take a close look at the picture above, Gemini staff and observers are standing on the telescope mount watching the view from within the dome. For both regulars and first-time visitors, the view is not to be missed.

Outside the telescope dozens of tourists watch the spectacle. They are just a small subset of people watching the spectacular view; about a hundred yards behind me are approximately three times this number enjoying the moment. At around $200 per person for taking the tour to 14,000 feet, I hope they are satisfied!

The visitors will be heading back to sea level soon. They'll stop on the way down to view the night sky from one of the best astronomy sites on the planet and then return to their hotel rooms a little before midnight. As they leave the summit, my workday begins.

Spreading your wings

The Smithsonian Submillimeter Array (SMA) appears to have deployed its dishes to their maximum extent. A few weeks ago I posted a picture in "Odd one out" where you can see them about as closely grouped as they can get, with the "sergeant major" to the left (see picture below). Now they're as far apart as I think they can get, obviously trying to maximise their delivered resolution at the expensive of sensitivity. I wonder what they're observing?

At this time of year the Galactic plane is roughly overhead at around midnight, so at sunset it'll be very low on the eastern horizon which is where the dishes are pointing. Maybe they're studying our Galactic centre? It's one of the hottest topics in Galactic astronomy these days.

Twin peaks

The last couple of nights have offered some of the more spectacular sunsets from Mauna Kea's summit. I've a few more photos to come! Above: distant Hualalai to the left, Pu`u Poli`ahu to the right, the usual ocean of low-level clouds beyond the peaks and beautiful post-sunset clouds above. Layers of vog are noticeable below Hualalai's summit. Don't forget that as ever you can see a much larger version of the picture by clicking on it.

Thursday's summit views

About half an hour before sunset the Kohala coastline 14,000 feet below is clear and the sunlight reflects off the Pacific ocean. Distant clouds on the horizon are a worry for tonight, but so far they haven't bothered us.

Well after sunset, Hualalai to the left, Pu`u Poli`ahu in the centre, Submillimeter Valley centre-right and red cirrus clouds above!

Yellow

The clouds were spectacular this evening, both to the east of us (above) and to the south (below). Fortunately by the time it got dark there were none overhead. We also tried to spot Comet C/2009 R1 (McNaught) but had little luck as it was lost in the twilight sky. Andrew Cooper may have had more luck tonight.

Hope I haven't said something wrong!

There's been a noticeable decrease in the number of comments recently, I hope I haven't said something offensive or anything like that! If it's down to a lack of content, then I definitely understand, I just hope those kind enough to read my posts understand things have become incredibly busy recently and it's hard to find time to put much thought into what I write here - so it's pictures instead!

Oh well, it's back on the mountain again tonight and I need to make the most of the next few visits. From November onwards my visits to this most amazing place will be very limited.

Cinder cones above the clouds

It's easy to forget we work on top of a volcano. Mauna Kea isn't active but is classified as dormant - certainly not an extinct volcano. It last erupted around 4,500 years ago but it will likely erupt again. No one knows when. The cinder cones that litter the summit area and the rest of the mountain bear testimony to a time not long ago when the mountain spat fire.

Light versus darkness

As the sun sinks below the horizon astronomers at Mauna Kea's summit start to work, the tourists leave for lower altitudes and the sky takes on some amazing colours. There comes a time when the light from the sun can no longer illuminate even the highest clouds and it tends to happen very quickly. One moment the cirrus clouds are bright red and the next they're a dull grey.

On occasion I catch the moment when day turns to night but it's not often. In this case you can see the dark clouds above and the brilliantly lit clouds off in the distance. In a few more minutes the distant clouds will be dark as well and shortly after that the sky will be dark. You wouldn't even know there are clouds there.

Well, you would if you're an astronomer working at one of the telescopes. Our data reduction pipeline shows that the stars aren't as bright as they should be, it even tells us by how much, so it's time for a backup plan until the clouds go away.