I'm currently stuck in Sydney airport on a 7 hour layover. Australian immegration law bars me from leaving the airport (it's a boot-able offense) and my attempts to video the rotational handedness of a toilet flushing ended poorly (these toilets have jets that direct water radially inward!). So as I sip my Victorian Bitter (how is that the Aussies are know for their beer?), I figured I'd answer a question that several friends have asked: "why do we need to go to the South Pole?" Why not do this somewhere closer, let's say Mt Palomar near San Diego or on Mt Wilson above LA?
The answers are that:
1) it's really dry at the South Pole and
2) the air is really still there over the winter
We're trying to look at microwaves (technically millimeter waves) left over from the Big Bang. We're stuck looking at microwaves because our expanding universe has stretched the wavelengths of the Big-Bang's afterglow from infrared into the microwave range. Wayne Hu from University of Chicago is well know for his animated gifs to explain cosmology, and here's his explanation of how our universe's expansions not only drags the galaxies apart but also stretches wavelengths of light into the red end of the spectrum.
The stable air is just as important. Generations of kids have grown up learning about twinkling stars from nurse rhymes, but it's a real pain for astronomy. Stars and distant city lights "twinkle" because of atmospheric turbulence, and it can make images look fuzzy. My friend Christoph Baranec designs telescopes with "adaptive optics" that can correct for turbulence with deformable mirrors. Below are pictures he took of Jupiter with his Robo-AO system on and off: