Operations at Kitt Peak
Hello from Kitt Peak again everyone. We are now more than half way through our observing run, everything is going really great, we are getting lots of spectra of our candidate galaxies. So far we have managed to do most of our top priority candidates!
Bill gave us a great post of what we are up to and some of the results we have taken so far. I wanted to talk a little bit more about the practical aspects of observing, to give you guys a feel for a typical night up here at the 2.1 meter. We have taken a lot of pictures and a few videos of the experience. Click the video thumbnails to watch each one.
Each night starts about 6pm, roughly an hour before sunset. Before we can do any of the fun stuff we have to get the telescope ready, this involves quite a few steps. The telescope itself is an amazing pice of kit but shares pretty much the same design as most telescopes since Newton’s time. Big curved mirror at the bottom, small mirror up the top, hole in the bottom mirror to let the light out again. It’s essentially a bit light bucket, catching photons which have been traveling happily and uninterrupted through space for billions of years.
The real technology lives at the bottom of the telescope, where your eye would normally go. On our telescope we have Gold Cam, a spectrograph and camera which allows us to analyse the light from galaxies and Voorwerpjes alike. By splitting up their light in to all its component colours, we can tell a great deal about each object, from how far away it is to what kind of atoms make it up and what state these atoms are in . To get the best out of this system however we need to prepare and calibrate it each night. The first thing we have to do is get the system nice and cold. Actually we need to keep it cold at all times, and when I say cold I mean cold. Your fridge freezer at home is probably about -10 degrees celsius, the coldest ever recorded temperature in the Antarctic was −89.2 °C, we have to keep the camera at a staggering -150 °C !!
To do this we cool it down with a supply of liquid nitrogen which we have to top up every 12 hours or so. Each afternoon, before we start observing and again in the morning before we leave, we attach a hose from a dewier to the bottom of the telescope and fill her up. If we didn’t do this then the camera would heat up to unacceptable levels and would have to go away for quite a lot of work before it could be used again.
Once we are sure that the telescope is going to stay nice and chilly we settle in to the observing room. This is adjacent to the main telescope dome and is where we will spend most of the night. To get a feel for where we work I made a quick video tour:
Sorry about the quality I had to use my laptop’s webcam to take it.
The first job of the night is to calibrate all our instruments. The measurements we are trying to obtain are very precise and so we need to make sure that we understand the response of our sensors. Imagine your personal digital camera fell in the bath one day, or was smashed against a wall or something to make it go a bit funny. In this mishap the sensor has got messed up, it still works but when you take a picture with it one side is a lot darker than the other. Instead of throwing the camera out you could try to correct for the damage. If you knew exactly the pattern of light and dark patches you could make some pixels brighter and some dimmer to compensate. So how do you figure out that pattern? Well you could take an image of a totally white background, or an image of something where you knew the exact value that every picture should have.
We do exactly this on the telescope each night, its called “flat fielding”. We also take calibration images of a special lamp which is built in to the telescope. This lamp makes a known pattern in the spectrograph and so lets us correct for any other issues we might have.
Having cooled and calibrated the system we are almost good to go. We look up the coordinates on the sky of the object we are interested in and slew the telescope round to point at it. As the earth rotates around its axis the stars appear to move slowly across the sky. It takes 24 hours for the stars to go all the way round and end up where they started, which may seem slow to us but for a telescope like the 2.1 meter, which is magnifying the field of view a lot, this movement is actually very quick. If we just left the telescope pointing in the same direction, the galaxy we are interested in would quickly move out of the telescope’s view. So we have motors which rotate the telescope in the opposite direction to the Earth’s motion, to keep the telescope pointed at the same patch of the sky. This process isn’t perfect, however, and the galaxy can still drift away if we are not careful.
Thankfully the telescope has another trick up its sleeve, if we find a bright star near to the galaxy we are interested in, we can ask the telescope to move in such a way that this star always appears in the same place. We call these stars guide stars and before we can take data we have to find one and lock on to it. That’s the theory at least; our system has been a bit temperamental this week. Occasionally we have to do things the old fashioned way, manually adjusting where the telescope points to keep the fuzzy blob which is our galaxy centered.
Each of the galaxies we are looking at are very faint. So faint that to gather enough light, even with a telescope as large as this one, requires us to stare at the galaxy for anywhere between 45 and 60 minutes. It’s quite a long time where there isn’t much to do appart form keep an eye on the galaxy, shoot the breeze, chew the fat and plan our next target. On particularly long exposures we have become fond of nipping up to the catwalk that runs along the side of the dome to take in the view. The Milky Way here is the best I have ever seen it! . You can see our bursts of activity in this time lapse of the observing room… we are not just slacking off… honest.
Once the exposure is done we move to a new object, but before we do we need to take yet another calibration exposure. This one is to make sure the position of the telescope isn’t causing the spectrograph and camera to flex out of shape, altering our reading. We also need to rotate the spectrograph to get the slit through which the light enters, in to the right orientation for what we want to look at.
We repeat the same process about 6/7 times a night and hopefully get 6/7 fresh galaxy spectra. Initially we can only tell a little from the data, we wont really get results until all those calibration test are combined with the galaxy spectra. Its a long, careful and very tedious process known as reduation, thankfully one which isn’t mine … its Drews.
At the end of each night, as the sun comes up about 4pm, we have to put the telescope to bed. This involves swinging it back round to its initial position and closing up the main mirror. With that done we can all go to bed as well, to dream sweet dreams of Voorwerpjes.