UF :: Astronomy

September 22, 2010
GTC Observatory
Roque de los Muchachos
La Palma, Canary Islands

All dressed up and no place to go! CanariCam, the University of Florida’s new high tech mid-infrared camera, is hooked up to the spectacular 10.4 meter (410 inch) GTC telescope, passing all of its commissioning tests so far with flying colors, and ready to start bringing in new astronomical data from deep space. But closer to home, a strong front has moved in and the mountaintop is covered in clouds, rain cascading off of the closed up dome, while the telescope sits idle, safely within its custom made garage.

The storm is bad enough that local authorities have activated emergency plans due to heavy rain and winds. On the mountain, movement is restricted between the astronomers' dormitory and the telescopes. If the weather continues to deteriorate, there is a possibility that the GTC telescope operator might decide to temporarily abandon the telescope. Here at the GTC, all is quiet and uncommonly empty as the rain continues to fall. Oh well, no scientific data today.



Into the early morning hours, the team has been checking out the workings of the University of Florida's CanariCam, designed and constructed by Professor Charlie Telesco and his team. They are making sure that it is properly aligned with the telescope, is communicating with the control room scientists, and is receiving images as expected. Until it clears up, however, the only “objects“ it can image are a couple of astronomers on the catwalk of the dome. The man on the right is doing the Gator chomp, imaged at mid-infrared!



Once the weather clears (maybe by Friday), the team can point to a few bright stars, check the pupil alignment, make sure the guiding of the telescope is working with the camera, and finish full commissioning of CanariCam. Then the real working science can begin.


Charles Telesco, Principal Investigator on CanariCam

Because the instrument must be able to pick out the relatively few photons from a distant protoplanetary disk or galactic nucleus, mixed in with millions of extraneous photons from the background radiation, the atmosphere, and the telescope itself, it is necessary to use a few astronomical tricks such as “chopping and nodding.”

Chopping is the process of offsetting the imaging by a tiny amount. Because the background radiation stays relatively the same for each offset image, they can be subtracted from the final image to eliminate the unwanted radiation from the final data. These offsets can be as small as 10 arc seconds (trust me, that’s a very tiny amount) every 5 seconds.

Nodding is the additional process of moving the telescope to a new nearby position once or twice a minute. This further refines the final image across the field of view, helping to eliminate the heat of the telescope itself. The combination of techniques allows CanariCam to detect faint objects with as little as a couple of minutes of exposure, and draw out the fine details that will reveal more knowledge of our universe.



All of this, of course, depends on the proper functioning of the telescope itself. A tour of the observatory with Chief of Operations Michiel van der Hoeven, originally from the Netherlands, reveals just how complicated this can be.


Michiel van der Hoeven, Chief of Operations, GTC

He explains that ventilation of the dome is critical. As any amateur astronomer can tell you, it does no good to have a large telescope and a clear night if your lenses are dripping with dew from the moist outdoor air. Also, air turbulence inside the huge dome can deteriorate the telescope’s performance.

An entire intricate system of cooling units (twenty large air conditioners), vents, and windows keep the interior of the dome cool and balanced so that when the dome is opened, the mirrors are at the proper temperature.

Moving a 400 ton telescope poses its own problems, but the GTC has that task well in hand. The entire telescope rests on hydrostatic bearings - not steel bearings, but rather a very thin layer of pressurized oil, which minutely lifts the telescope and allows it to glide with almost no friction. A child pushing against the telescope’s frame can move the entire assembly, giving a few visiting children bragging rights. “I moved a 400 ton telescope with my bare hands."


Closeup of bottom edge of telescope dome resting on pressurized oil, the overflow dripping into a pan

Although the GTC is functioning and busy with astronomical projects, aspects of its operation are still being worked on. The large ventilating windows on the dome, which will allow the flow of outdoor air to keep the telescope cool, are not fully operational as yet. Also, the dome doors do not fully open, limiting the telescope to a maximum elevation of about 70 degrees, plenty for important work but not yet 100%.

The 36 segmented mirrors are each separately controlled by motors mounted on their backsides. These allow fine adjustments to be made to their surfaces, sometimes as small as 2 nanometers (one billionth of an inch!), making sure the mirrors are in fact working as one large almost perfect mirror surface.


View of the rear of a spare segmented mirror

Alien asteroid belts and the secrets of our Milky Way's center must wait, however, as the rain continues to beat against the windows of the control room. Twenty astronomers and observatory staff were crowded in here just a few days ago, but now it contains only team member Frank Varosi, continually massaging the software interfaces and controls, a lone telescope operator, and me - an amateur astronomer having the experience of a lifetime.


Frank Varosi, Senior Software Engineer



Terry Smiljanich