My last observing run at Cerro Tololo, we were observing in “grey” time, when the moon was between 3rd quarter and full. So the dark sky only lasted a few hours. Now we are here during dark time, the days around new moon. Cerro Tololo is a nice, very dark site… perfect for astronomy. There is a bit of light pollution from La Serena and Coquimbo in the east and Vicuña in the north, but the sky is very dark, especially without the moon up. A large part of what makes this site so important to optical astronomy is this darkness, which is a rare commodity in the modern electric light-filled world.
I realize how dark the skies are here every time I go outside now. The Center of the Milky Way is passing overhead and it just screams out at you to be noticed. You can see it clearly on the right side of this picture, shot by Roger Smith of NOAO/AURA/NSF. It shows the 4-meter at Cerro Tololo shot at night. This is what the skies look like here. Admittedly this picture goes a bit deeper than human vision, but I would swear it isn’t much deeper. At home, we can’t see the Milky Way easily, even 15 miles from town, because of the light pollution and the fact that the Galactic Center is very far south. Here, you can’t avoid it! The Large and Small Magellanic Clouds, two irregular galaxies orbiting the Milky Way, are clearly visible to the human eye (they are on the right side of this picture).
And just a few minutes ago I saw something I have never seen before, Zodiacal Light. I am seeing sunlight reflecting off dust grains in the plane of the Solar System. Something only possible because of these extremely dark skies. Cool!
