Pictures of the SPT from this season

Here are some nice pictures of the South Pole Telescope from this season.  Enjoy!

Walking out to the telescope

It's not the telescope, but...

Sweeping snow off of the boom

The rack of readout electronics

Nick explaining how it all works

Chilling on the boom

South Pole Igloo

A few weekends ago, my friend Sam came up with a great Sunday afternoon activity - build an igloo!  We specifically decided to wing it with out looking up any instructions, just to add to the adventure.  That Sunday, we located a shovel, a wood saw, and a snow saw, and headed outside to try our hand at snow-construction.

Finding good snow that could be cut into blocks was not a problem.  But the fact that it was -35 degrees F outside meant that blocks did not melt and re-freeze together with handling.  We started by building a ring of blocks ~8 feet in diameter.  After several hours we had a wall which was shoulder-high, but was not closing over the roof fast enough.  The solution; build a central pillar to support the roof in the middle.  It may be unconventional, but it worked well!  Now we had a 2-room igloo.

After 5.5 hours, we finally placed the last block in the ceiling.  Unfortunately, this was just a bit too long, and we missed dinner.  We melted our frozen beards in hot tea and soothed our tired backs with plates mounded high with left-over chicken and beans.

The next weekend, I came to the conclusion that it would be a good idea to sleep in the igloo.  After talking to the winter station manager, I located a couple of sleeping pads and two -40 deg sleeping bags.  Nobody else was foolish enough to go with me, so I trudged out of the warm station at 10pm on Friday night in the 24-hour sunlight with a gigantic duffle bag, and set up for the night.  I put one sleeping bag inside of the other, and set down the two ridge-rest sleeping pads.  I was not super tired so I read a book for some time; however my hands kept getting cold and eventually I gave up and put the book away to go to sleep.  The sun does not set until March, so the igloo maintained a cool blue color throughout the night, never getting anywhere close to dark.  None-the-less, I slept in 2 hour blocks through most of the night.  At 6:30am my feet started to get cold, and by 7:30 I was ready to get a move on.  I suited up, stuffed the sleeping bags and pads into the duffle, and headed into the station.

Ahhh, the warm station, hot breakfast, steaming cups of HOT-chocolate... luxury!  The thermometer read -47 deg F.  If I were still in boy scouts, I would be 79% of the way towards the "100-degrees of frost" badge!  Sleeping out in the cold meant that I actually got up in time for breakfast, literally the only time I managed this feat the entire time at pole.

Sam, the man with the plan, sporting an awesome ice beard.

Shoveling out blocks.  This was back-breaking work!

Our block collection.

Adding the finishing touches to the igloo.

There she is!  Not the prettiest thing you ever did see, but functional.

My ice-beard and powdered hat.

Yeah... my balaclava froze to my face, and I had to melt it off once inside.

Looking straight up at the central pillar from inside the igloo

Coming back to the igloo to sleep

Self-portrait inside the igloo

The central pillar of the igloo.

Working on polcal

South Pole Telescope

One of the main objectives of my trip to pole this year is to help with "polcal" measurements.  In this post, I will describe these measurements.

Last season, 2011-12, we completely replaced the detectors on the telescope with a new focal plane.  This new focal plane is sensitive to the polarization of the light that we observe.  Light is an electromagnetic wave, and the polarization of a wave of light is the direction that the electromagnetic wave is oscillating in.  Our polarization-sensitive detectors are organized into pixels, where each pixel has two detectors that are sensitive to orthogonal polarizations.  In simple terms, the two detectors in a pixel effectively form a cross.

With this "SPTpol" camera (short for South Pole Telescope polarization), we are studying the polarization patterns of the Cosmic Microwave Background (CMB).  This experiment requires us to know the precise orientation of each detector, and therefore what polarization each detector is sensitive to.  This is where "polcal" comes in.

"Polcal" is our short-hand phrase for "polarization calibration."  The goal is to measure the orientation of polarized light that each detector is sensitive to, to an accuracy of less than a degree.  We accomplish this measurement by installing a source that produces light of a known polarization, pointing the telescope at the source, and measuring the response of each of the detectors.  The source is set up as follows; a "black-body" source provides the light.  As a reminder, the SPT sees light that has a wavelength of approximately a millimeter, which is a much longer wavelength than our eye sees.  The black body source is heated up to 750 Kelvin, and radiates light.  This light is focused by a plastic lens, then goes through a polarization grid.  The grid allows light that is polarized in one direction to pass through, and absorbs all other light with a different polarization angle.  This contraption produces a beam of polarized light that we can observe with the telescope.

The final piece is that the polarization grid described above mounted on a rotation stage, and the angle is rotated in steps of 15 degrees.  This way we can fully map out the detector response as a function of the polarization angle of the incident light.

Ben working on the polcal source box

Inside the box.  From bottom to top is the sense, polarization grind #1, then the rotation stage with the bar-code and grid #2.

Still not working...

We place this source on a stand ~3 km away from the telescope. The telescope is set up to focus on light from the CMB, which is effectively at a distance of infinity.  We can adjust the focal length of the telescope some, but 3 km is about as close as we can get. We put the source box on a stand that is surrounded by a reflective pannel, which reflects the sky.  The ground radiates too much light (at the frequencies that the telescope can see), and the telescope detectors are optimized to observe the sky; thus the reflector is necessary to keep the detectors working properly.

The reflector

My job has been to install or take down the box at the 3km reflector, make sure everything is working properly, and take measurements.

Driving out to the 3km source.  Can you see the reflector?

Looking back at the SPT and the station from the 3km source.

Raising the source box up to the platform on the reflector with Ben and Clarence.

Installing the source box on the reflector platform.

The source box weighs about 150 lbs and it unwieldily.  We install in on the platform on the back of the reflector using a chain hoist.  This is not so easy when it is -25 deg F outside!  It usually takes four people to install the source.

It is pretty cool to be out at the source.  The source is 4 km from the station, which is far enough to really feel the isolation of this amazing place.

Looking into the distance

Once everything is working, we can take a moment to enjoy the location.

Lounging on "The Beach"

SPT!