Cerro Tololo: A Summit of Telescopes

Our arrival on Cerro Tololo was late in the afternoon after a full day up at Cerro Pachon and the Gemini South campus. While the two mountaintops are relatively close to each other (10km), it takes hours to get from one to the other view the high altitude switch-back roads that lead along a generally more approachable path to the mountains that a direct route. Cerro Tololo itself is 2207m in altitude, a good preparation for our higher altitude stay at ALMA later in the trip. Cerro Tololo is home to the Cerro Tololo Inter-American Observatory, the CTIO.

Cerro Tololo Summit Map

Cerro Tololo Summit Map (Wikimedia Commons)

Arrival on the summit campus gave a very rapid impression of the overall sprawl. There are telescope domes everywhere up there!  The mountain’s top contains a plateau with the 4m Blanco telescope and the 1.5m SMARTS telescope dome being the most prominent. There are some nine instruments on the top plateau alone. A little down the mountainside is a group of small instruments in a region that some call the “mushroom garden”. Plant a mirror and watch the dome grow? In this area there are 16+ domes. Going further down still, there is the cafeteria and the dormitories for administration and visiting astronomers. We were in a dorm lowest down, closest to the SARA telescope facility.


The SARA observatory facility, a little further down the mountain from the rest of the observatories.

SARA stands for the Southeastern Association for Research in Astronomy, a group of some 13 college, universities and institutes which control a series of telescopes for their use. A friend and colleague of mine, Tom Rutherford, gets time on the SARA telescope on Cerro Tololo, and the whole process is done remotely. Robotic technology has been making astronomical observing much more economic and streamlined.

CTIO Mushroom Garden

The telescopes on CTIO just below the main plateau. GONG, 2MASS and others reside here.

The mushroom garden is a real collection of telescopes from all over. There is a GONG facility (Global Oscillation Network Group) which has many facilities all watching the Sun. They study surface oscillations for the field of helioseismology, amazing stuff! Others in the garden include scopes for SMARTS, PROMPT, WHAM, LCOGTN, and 2MASS.

This is the UMass 2MASS telescope.

This is the UMass 2MASS telescope.

The 2 Micron All Sky Survey (2MASS) also has a telescope here. This one run by UMass, the 2MASS system did a huge near IR (I, J, and K) survey of the sky, one of the earliest. using two 1.3m telescopes: one at CTIO and one in the north at Mt. Hopkins.

On top the mountain are the two big facilities: the 4m Blanco Telescope and the SMARTS 1.5m.  The SMARTS 1.5m scope is a Cassegrain focus system with two focal lengths available depending on which secondary mirror is installed: f/13.5 and f/8. Two instruments are now available, R-C Spec and CHIRON. CHIRON is a precision spectrograph, a fiber fed echelle system like that we use at Phillips Exeter, only with higher dispersion  and resolution for making very fine measurements in radial velocity.

CTIO SMARTS 1.5m Telescope

The SMARTS 1.5m Telescope.

Cassegrain focus on SMARTS

The Cassegrain focus on SMARTS.

SMARTS control panel

The SMARTS control panel. It is a thing of beauty and simplicity.

The largest telescope on the mountain is the 4m diameter Victor Blanco. Opened in 1974, this is very similar to the 4m telescope on Kitt Peak in Arizona. The telescope has several instruments: a wide field imaging camera (DECam) and low to medium resolution spectrographs, COSMOS and ARCoIRIS. The DECam is used for data collection in the Dark Energy Survey program, kind of like a new Sloan Sky Survey… more on this at their homepage here: http://www.darkenergysurvey.org/the-des-project/overview/

The 4m Blanco?  It is a pretty huge machine, as you can imagine!

4m Blanco CTIO

The 4m Victor Blanco Dome at CTIO. That is one BIG dome! This is a shot taken by moonlight on our first night.

4m Blanco Controls

4m Blanco Controls: everything from weather to CCD and spectrograph operations are controlled here.

4m Blanco Pan

This is the whole dome interior. Modern photo software allows great opportunities to take photos of large spaces! This is a panorama shot inside the 4m dome.

Our first night on the mountain, we stayed up to observe through a high layer of cirrus clouds and the waxing gibbous moon. Conditions were certainly not optimal, but the views of the milky way, even with moonlight and clouds, was pretty outstanding!

The summit from lower down the mountainside.

The summit from lower down the mountainside. On night-1 we had both moon and clouds, but the views were still inspiring.

Mushroom Garden at night

Looking out from the summit road towards the multitude of domes at night.

Our second night on the mountain proved to be the best. Some high cirrus clouds whisked away into the distance, and the sky turned a deep blue for sunset on the mountain. A tradition among astronomers is to get all the observatory equipment ready for the night, cool things off, and watch the sunset. We had a glorious view!

Sunset on CTIO1

Sunset on night 2 from CTIO: the distant foothills are lovely, all aglow with the evening sunlight.


Looking at the mountains surrounding Cerro Tololo, the views take one’s breath away! The sunset just made it all the more colorful.

sunset CTIO night 2

The sunset itself on night two.

Using a portable telescope, the group had views of some of the prominent southern hemisphere deep sky objects and Saturn… breathtaking!  The air is so steady at this site, that the Cassini Division and the Crepe Ring were clearly visible in a 10″ telescope!  Needless to say, there were a lot of oohs and ahhs.  With the moon still up, I decided to get some sleep for the first half of the night and get up at 3am to catch the moonset and the moon-less views of the milky way. None of us were disappointed, though we were a little sleepy the next day!

Night 2 with moon

This image was taken earlier in the evening of night two while the moon was still up. The views of the milky way are still more incredible here than it is in 90% of the rest of the inhabited planet.


Looking towards the west in this image, the mountain summit and domes are visible on the horizon. The Milky Way was bright enough to walk about easily without a flashlight.


Once the moon had set, the Milky Way just popped out! This is a 30 second exposure with a fisheye lens at about 4am local time. Both the large and small Magellanic Clouds are visible.

If you happen to be in Chile, close to La Serena, have some free time, and some curiosity, you should definitely get in touch with CTIO and see if you can get a tour. It has some of the best observing conditions on the planet, and is well worth the visit…. enjoy the skies, the people, the wildlife and the crisp air!

About johnb

- Director of Grainger Observatory, Phillips Exeter Academy. - Variable-star-crazed astronomer, but have done research in other areas. - Drummer, archer, pilot, chef, friend, pet owner, husband, father, Train-nut.
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2 Responses to Cerro Tololo: A Summit of Telescopes

  1. I thought the 2MASS telescope was run by Caltech.

    • johnb says:

      UMass and Caltech collaborated on the original 2MASS survey which is now complete. IPAC and UMass are now woring on followup work in the IR, SYNOPSIS.

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