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!

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Cerro Pachón & Gemini South Telescope

Gemini South is one of a two part observatory system, the Gemini Observatory. The northern counterpart is at Hilo, Hawaii, while the southern telescope is located on Cerro Pachón, a 2682m (8799 feet) tall mountain in Chile.  This is one large telescope, with a primary mirror diameter of 8.1 meters!  It collects a lot of light, and at this location, it can do just that. Cerro Pachón has some of the darkest and steadiest skies in the world. Combine that with the instrumentation on board this telescope, and the total integrated system produced results better than the Hubble Space Telescope!

Gemini South Dome

A view of the Gemini South dome from the far side of the mountain. That is one big dome!

The telescope is a somewhat unusual design in terms of mounting: it is on an altitude-azimuth configuration. The azimuth bearing is literally the steel rotating platform of the telescope resting on a steel azimuth ring. The ring is set atop a concrete telescope pier. To allow for smooth movement, oil is pressurized and pumped into the region between the two steel plates.  This setup has withstood all the seismic activity that Chile has thrown at it, but it was somewhat damaged during one of the strongest quakes in recent years which caused the mount to slide side-to-side with such force that the restraining plates were damaged.

Instrument package for Gemini South

This is the Cassegrain focus location for Gemini South. The instrument package hangs between the two stairways. The blue disk on the floor is the telescope’s azimuth bearing plate.

The altitude bearings are a little smaller but also float on a thin film of pressurized oil. The pumps for both axis can be heard constantly in the background of this rather industrial setting. Astronomers immediately know when something is wrong if those pumps are not making their usual noises.

Being an altitude-azimuth arrangement, this means that the field of view at the image plane rotates!  They compensate for this by de-rotating the entire instrument package at the Cassegrain focus of the telescope (hanging underneath the primary mirror). As the field rotates, this package rotates precisely in the opposite direction to counteract this.

One of the most amazing packages on board Gemini South is the GeMS, the Gemini Multi-Conjugate Adaptive Optics System. Now, you might already know about adaptive optics. A laser is projected into the sky to make a fake guide star, which the telescope system sees and senses. As the atmosphere makes this star wobble, small mirrors are used to move the image of that star back into place. This happens at a rate of up to 1000 times each second in both axis: up/down, and left/right. To make the system better, Gemini South uses five laser beams into the sky. This allows them to not only correct the errors caused by atmospheric seeing conditions, but also to correct for predicted motions in the stars’ positions!  This allows the telescope to image down to 0.1 arc-second seeing!  That is very sharp indeed!

GS primary mirror

Gemini South’s primary mirror. That’s 8.1 meters of diameter. The mirror is not coated with aluminum like most astronomical telescopes, but is coated with silver. This makes it more reflective to infra-red wavelengths. To the left of this image is a large metal “box”. This is where the laser is installed for the GeMS.

At this altitude, and given that it was winter there in June, snow was present on the mountain and those surrounding. The views here are lovely, as one would expect from an altitude of 8900 feet.

Winter here in June. Yes, that is snow!

Winter here in June. Yes, that is snow!

Controlling the telescope and all the associated equipment is done from the central control room. Eventually all this will be done from operations at AURA back in La Serena. The control system includes everything necessary for all observatory components, including: ventilation/cooling, instrument status and control, telescope pointing, oil system control, sky conditions and weather forecasts, and more. The system has redundancy with dual control desks.

Gemini South Control

Gemini South Control

Gemini South Control Room

Gemini South Control Room

All in all, the Gemini South observatory is an amazing place! All the instrumentation and systems that work together make for an astounding ability for data collection… and also a huge need for systems integration and maintenance. If you have the opportunity, I highly recommend a visit!

All of Gemini South

All of Gemini South: an indoor panorama.

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Panoramic Chile

One of the things I like to do when traveling is to take photos that give an overall perspective to the surroundings. While this is getting to be easier with cell phones and their build-in 3D and spherical photography applications, not much can beat a full frame DSLR or film camera taking shots that are later merged to form a solid, high resolution image. These were stitched together in Adobe Photoshop with minimal post processing. The images are not cropped, so that you can see all the data. Enjoy!

Santiago seen from the top deck of the Gran Torre Santiago

Santiago seen from the top deck of the Gran Torre Santiago, the tallest building in South America (64 stories). The view is spectacular.

Laguna de Chaxa

Laguna de Chaxa, home to very salty water, Los Flamincos and brine shrimp galore.

Geology of the Atacama Desert.

Geology of the Atacama Desert.

View from the top of Cerro Tololo just before sunset.

View from the top of Cerro Tololo just before sunset.

View from the top of Cerro Pachón.

View from the top of Cerro Pachón.

View from the top of Cerro Pachón.

View from the top of Cerro Pachón.

ALMA seen from a higher vantage point.

ALMA seen from a higher vantage point.

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Under the Stars of Cerro Tololo: Night 2

Night Two on Cerro Tololo was tremendous. We started out the evening with a viewing of the sunset from the edge of the mountain top just outside the central gathering place: the cafeteria 😉  Food on the mountain, by the way, is delicious, plentiful and healthy. We had hoped to catch the green flash, but we had some low clouds floating in the western horizon. No flash, just gorgeous views of the mountains as the landscape turned red.

CTIO Night 2: Sunset Panorama

CTIO Night 2: Sunset Panorama

CTIO Night 2: Sunset

CTIO Night 2: Sunset

Once the sun had set completely, the stars came out rapidly. The moon was in a waxing gibbous phase, which meant that much of the night would be illuminated quite well: no need for flashlights to get around the mountain until the moon set. Here is a 30 second exposure of the Milky Way, which was VERY visible, while the moon was still high in the sky. Imager: Nikon D810a 16mm f/2.8 fisheye 30 seconds.

CTIO Night 2: Milky Way with Moon

CTIO Night 2: Milky Way with Moon

It is pretty exciting to be seeing the Milky Way so clearly even with a gibbous moon high in the sky. The transparency at CTIO is tremendous with some of the best seeing conditions I have ever witnessed.  One very obvious feature of the Cerro Tololo sky is that there is no scintillation. Stars do not twinkle! They are steady and just hang in the sky. If this was the sky with the moon above the horizon, what would it look like once the moon had set after 3:30am or so?  I went to bed and set the alarm for 3am. That was a very good decision!

As the alarm went off, I was pretty sleepy, but very excited by the prospect of getting some stunning images of the sky. Stepping out of the dorm room onto the sandy pathway, it was more than obvious that the moon had set for our side of the mountain. Shadows of Cerro Tololo were being cast by the moon onto the eastern peaks. The snow line was still clearly visible, but that shadow was rising rapidly as the moon went further below the horizon. Grabbing the camera and tripod, I made my way outside. Several of us gathered for the stunning view: a Milky Way from horizon to horizon, with dark lanes, bright nebulae, clusters galore, and color! It is very difficult to convey just what the scene looked like. There were so many stars that constellations were sometimes impossible to identify, giving strong evidence to the native constellations, the dark regions of the Milky Way become the Llama, the Toad, the Serpent, the Shepherd, the Fox, all became visible as dark shadows over the blazing Milky Way.

CTIO Night 2: Milky Way

CTIO Night 2: Milky Way. A single 30 second exposure. D810a 16mm fisheye f/2.8

CTIO Night 2: The Milky Way with SMC and LMC

CTIO Night 2: The Milky Way with SMC and LMC. A single 30 second exposure 16mm f/2.8 D810a.

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Under the Stars of Cerro Tololo: Night 1

We arrived on Cerro Tololo after the day’s approach through the desert and the prior visit to Cerro Pachón. The roads are winding, often edge-less, packed gravel and sand pathways that lead up to both mountains. There is a split at the moment the road heads out to one observatory peak or the other. Cerro Tololo has been a site of observatories since 1965. It was studied and identified as an appropriate site in the 50s, and it is amazing that people were able to get up to the peak sans roadway. Images show people on horseback threading their way up.

The skies?  They are amazing. We’ll get to that. Night one was a little on the cloudy side from about sunset on to 3am or so. Before heading off to bed, we stayed up near the 4m Blanco courtyard and just looked up. The waxing moon was out, but one could still see Milky Way and the brighter southern stars without any issues through a light covering of cirrus. We had a smaller scope to look at the planets and some of the brighter deep sky objects, and enjoyed that as the clouds came and went. We also had a little fun with the moonlight, which, when used properly, can be a perfect illuminator for long exposures.

CTIO Night 1: The 4m Blanco by Moonlight

CTIO Night 1: The 4m Blanco by Moonlight

CTIO Night 1: The ACEAP team by moonlight

CTIO Night 1: The ACEAP team by moonlight

At about 3, I struggled to get out of the warm bed and out into the driveway to our dormitory. The dorms are located a ways down the peak, so I did not intend to work my way back up to the 4m plateau, but just wanted to go out and look up. Sure enough, the moon had set and the skies were clearing rapidly. There will still some high clouds, but nothing obscuring the skies as before. What I saw was amazing, just phenomenal: Milky Way illuminated the sky from horizon to horizon!  It was even bright enough to allow me to walk around without a flashlight. That’s a lot of stars! That is a clear site!  I ran back inside to get some more clothes on(!) and to grab the Nikon D810a with tripod and a 16mm fisheye. This is the view… amazing. One word.

CTIO Night One: Milky Way

The Milky Way seen from CTIO on night one. The view is so incredible that it is difficult to see constellations in the traditional way. Nikon D810a, 30s, 16mm f/2.8.

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