Cerro Tololo

Saturday, April 26 – Day 130

I’m the only American on the tour today and it’s done entirely in Spanish. That’s OK, my Spanish is getting pretty good and I know enough about telescopes to make it work.

There are numerous observatories atop Cerro Tololo, but we common folk are not allowed anywhere near the really cool stuff. We started with a tour of a 1.5 meter telescope that is housed in one of 5 smaller observatories that are right next to Cerro Tololo. We’re able to walk around and get right up next to this scope, then the tour guide described how it works and moved it around and to show us all the parts.

Inside Cerro Tololo, we are only allowed to stand in one spot, and not even the tour guide gets to be close to the instrument. With a primary mirror of 4 meters (over 12 feet), it is absolutely huge, and just being able to walk in and look at it makes the trip worthwhile. Even though this telescope is a bit of an antique, it costs about US$10,000 per night to use, and every night is booked for the next three years. One of the current projects is, you guessed it, confirming that Lyman-alpha emitting galaxies at redshift 3.1 are the first high-redshift items to be identified as the precursors of typical present–day L* galaxies. For a sense of scale, look at the guy walking at the base of the observatory.

The largest telescope on the mountain is the Gemini South 8.1 meter scope. Its primary mirror is 26 feet across, making it one of the 5 largest telescopes in the world, and it cost US$176 million to build. No wonder they won’t let tourists come in and kick the tires.

One of the more interesting points that the guide made, was that professional astronomers actually spend very little time looking at things through these big telescopes. Almost all of the telescope’s time is devoted to capturing non-visible information. Starlight is diffracted and its spectrum is analyzed reveal the various elements of its composition. Redshifts and blueshifts are analyzed to show if things are coming or going, and all of this is being done by computers that are sometimes on the other side of the world. Pretty crazy stuff.