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Because the South Pole is probably the best place on Earth for this telescope. It is extremely dry, making the atmosphere exceptionally transparent for SPT.




Even though the universe is glowing with the cosmic microwave background (CMB) light, from the ground we can only view this background light through the Earth's hazy atmosphere. The component of the atmosphere that causes the biggest problem for these observations is simple water vapor. Just like water in food absorbs radiation in a microwave oven, which heats the food, water in the atmosphere absorbs millimeter and sub-millimeter wavelength light from the sky (i.e., the CMB). In addition to absorbing the light we are looking for, water vapor also creates a false signal. It emits light at these wavelengths, and since water vapor is not uniform (consider how patchy clouds often look to us), the light it emits makes the sky look brighter in some spots than others (which is exactly what we are looking for in the CMB). In order to see faint variations in the CMB's brightness, we need to minimize these effects.




The South Pole lies on a plateau at a high altitude (almost 2 miles), elevated above much of the normal water vapor in the atmosphere. The extremely cold weather also reduces water vapor in the air. You may have experienced this phenomenon if you have been in Chicago, or a similarly cold place, in the winter. You probably noticed that the air was dry, the sky was clear, (and lip balm was a necessity!). The South Pole is much colder and thus much drier then Chicago. These desert-like conditions make the South Pole a great site for a millimeter/sub-millimeter telescope.


The South Pole's unique position on the globe makes it an even more extraordinary site for this telescope. During the winter, sunshine does not reach the South Pole; nighttime (or daytime in the summer) extends for months. The lack of daily sunsets and sunrises makes the atmosphere extremely stable. Conducting observations in the winter also removes another contaminant to millimeter/sub-millimeter observations - the sun. All these factors conspire to make the South Pole the perfect place for the South Pole Telescope.

SPT Collaboration Chicago Berkeley UIUC Case JPL Smithsonian McGill U Boulder Davis