NOIRLab
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Cerro Tololo Inter-American Observatory
Where the Dark Energy Survey ran its camera for six years, mapping 300 million galaxies to measure how fast the expansion of the universe is accelerating.
- Where
- Coquimbo, Chile
- Coordinates
- 30.17°S 70.81°W
- Since
- 1963
- On the map
- Show me
- More
- noirlab.edu
The sky from here
This is a zone 2 sky — rural on the nine-grade scale, Bortle 2–3, reaching roughly magnitude 6.7–7.5 unaided. The Milky Way is structured and obvious. Light domes sit low on the horizon over distant towns, and the rest of the sky is genuinely dark.
That grade puts 107 of the catalogue within easy reach of 10×50 binoculars and 107 within a 130mm — 44 of them need no instrument at all. There is nowhere darker worth driving to; this is already among the better skies on the planet.
There is no season here in which the sky fails to get properly dark — the Sun clears eighteen degrees below the horizon on all 365 nights.
At its highest the galactic centre stands 89° up, which is the difference between a Milky Way with depth in it and a smear along the horizon. Of the 110 Messier objects, none are circumpolar and 4 never rise.
Of everything in the catalogue, Southern Pinwheel, Butterfly Cluster and Ptolemy's Cluster are the best served here, climbing to within a few degrees of straight up — an object at the zenith is being seen through the least air it will ever be seen through, and the difference against the same object low in the south is not subtle.
Against that, Bode's Galaxy and Cigar Galaxy never clear the horizon here at all. No amount of aperture or patience changes that; the only remedy is to travel.
Read at 30.17°S 70.81°W. Darkness is estimated rather than measured; everything else follows from the latitude and holds along the whole parallel. How accurate this is.
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Questions
What part of the sky never rises at Cerro Tololo Inter-American Observatory?
Everything north of declination +60°. From 30.2°S that is a cap 30° in radius centred on the north celestial pole, which is 6.8% of the whole celestial sphere. That part of the sky is not merely a winter object or a difficult one; it is geometrically unavailable from this latitude. The equivalent cap around the south celestial pole is the compensation, and it never sets.
How many hours of true darkness does Cerro Tololo Inter-American Observatory get?
Between 6 hours 41 minutes on the shortest night of the year, around 21 December, and 10 hours 57 minutes on the longest, around 21 June. Astronomical darkness is the Sun more than eighteen degrees below the horizon, which is a stricter thing than the Sun being down. The sky here reaches it on every night of the year, which is not true much further from the equator.
When is the Milky Way best from Cerro Tololo Inter-American Observatory?
June and July, and the timing is the whole point. The core transits at midnight around 17 June everywhere, but at 30.2°S that is the depth of winter: the longest nights of the year, sitting underneath the galaxy at its highest. Northern sites get the same transit date during their shortest and least dark nights. It is the single biggest structural advantage a southern observatory has.
How far is Cerro Tololo Inter-American Observatory from the other sites on this map?
The nearest is Vera C. Rubin Observatory, about 10.0 km to the south-east. That is also the nearest other observatory, with the next one 10 km beyond it. Distances are great-circle, so they are what a signal covers rather than what a road does.