B. Geerts and E. Linacre

7/'98

South Pole Observatory, located at 2841 m on the Antarctic ice dome. The ice has drifted a little since the station was established, so it is now 330 m away from the geographic South Pole. The living quarters for scientists are in the central gray dome. The aircraft runway starts in the lower right corner of the picture.

The Antarctic atmosphere is consistently much more transparent in the submillimeter-wave atmospheric windows than that at any other existing or proposed observatory site on Earth. This is partly because of the elevation, which reduces the attenuation of light by our atmosphere, partly the air’s low aerosol concentration, and mainly because of the coldness, which reduces the obscuration by water vapour.

Other major astronomical sites are Hawai'i's observatory on top of the 4,180 m Mauna Kea and the European Southern Observatory in La Silla, in Chile's Atacama desert, the world's driest desert. Of these sites, the integrated atmospheric water vapour content (known as the precipitable water (PW), Section 6.6) is lowest over the South Pole (Fig 1). In fact, the summertime PW over the South Pole is less than the wintertime PW over the Atacama. Water vapour is the main absorber in the sub-millimeter (mainly infrared) spectrum.

Also, the lower half of the troposphere above Antarctica is extremely stable, with a deep inversion present mainly in winter, so that there is very little shimmer of galactic light due to convection. The result is that the air more transparent, the sky clearer and the stars brighter.

Fig 1. Mean precipitable water (mm) at three major observatory sites (from (2)).