Sunday, April 28, 2013

Adventures at the James Clerk Maxwell Telescope

Two weeks ago I was privileged to be invited up to the summit of Mauna Kea to the James Clerk Maxwell Telescope as part of my job. Well, I say that, but really the only reason I was there was as a "warm body" – safety regulations require a minimum of two people together up at the summit at all times, in case of medical emergency, so my specific job had nothing to do with it.

Which I don't mind at all! It meant I got to go up with no real responsibilities besides crisis management in the event that something came up, which it didn't. I was therefore free to get a tour of the telescope that I officially work for, and wander around to get some pictures.

For instance, this black machine here is the water vapor meter, whose output I work with a lot. It measures the amount of water vapor in the air, which directly (and dramatically) affects the opacity of the atmosphere in the sub-millimeter wavelengths we observe in. It's been having some issues, so it was actually replaced with a different (silver) one just last week.


This big blue machine down here is SCUBA-2, the Sub-millimeter Common User Bolometer Array (2). This is another instrument whose output I work with on a regular basis. It's basically the best sub-millimeter camera in the world today.


It also happens to be the coldest place in the known universe. You think outer space is cold? Out far away from hot stars and galaxies, in the inter-galactic voids of space, the temperature can drop to about 2.7 kelvins, the temperature of the cosmic microwave background radiation, which is about 2.7 degrees Celsius above absolute zero (which is -273.15 °C or -459.67 °F).

That's cold alright, but it's still quite a bit hotter than the temperature of the SCUBA-2 imaging arrays, which are kept a mere one-tenth of a kelvin above absolute zero.

(The reason for such cold temperatures is that, in order to get a reasonably high signal-to-noise ratio from the electronic imaging arrays used in astronomy and digital cameras, the imaging array itself has to be cold enough that it's not emitting too much electromagnetic radiation in the portion of the spectrum it's trying to take a picture of. Consumer digital cameras work because they aren't glowing at visible wavelengths. Another way to think about it is that trying to take images in the sub-millimeter portion of the spectrum [which comes from objects that are themselves quite cold already] is like trying to take pictures with a digital camera that is on fire. The amount of light given off by the camera at that point is so much that you won't catch much light coming from what you want to photograph by comparison.)

Anyway, this is a panorama I took from behind the telescope looking up at the back of the dish. It's slightly misleading; it looks like it's looking at the sky, but that's actually the world's largest piece of Goretex (no joke). It also looks like it has a square opening, but that's a result of the image stretch due to the panorama. It's actually more like a rectangular slice in the side of a cylinder. (Unfortunately I forgot to take a picture of it from the outside.)


Finally, here's a high dynamic range image of the back of the dish. I had to take this one lying on the floor to get it all in, hence the slightly off-horizontal angle.


For those who don't know what the JCMT looks like from the outside, here's a picture of it from back in 2010 while I was up on a summit tour. It's the white cylinder on the middle-left. The opening is on the left side of the cylinder in this picture (the whole building rotates to point the telescope), but it wasn't actually open at the time.

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