Places · Observatory
Las Campanas Observatory
Home of the twin 6.5 m Magellan telescopes, and the site being prepared for the Giant Magellan Telescope's seven 8.4 m mirrors.
The sky from here
The sky over this spot is zone 2 — rural, Bortle 2–3, with a naked-eye limit around magnitude 6.7–7.5. 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.
Against that sky 107 of the 110 Messier objects are straightforward in 10×50 binoculars and 107 in a 130mm, with 44 reachable by eye alone. There is nowhere darker worth driving to; this is already among the better skies on the planet.
The Sun drops far enough below the horizon here for full astronomical darkness on every night of the year — which is not true of anywhere much further from the equator.
At its highest the galactic centre stands 90° 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 3 never rise.
The sky here is kindest to Southern Pinwheel, Butterfly Cluster and Lagoon Nebula, each of which passes within a few degrees of overhead — 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 29.02°S 70.69°W. Darkness is estimated rather than measured; everything else follows from the latitude and holds along the whole parallel. How accurate this is.
Nearby
Questions
What part of the sky never rises at Las Campanas Observatory?
Everything north of declination +61°. From 29.0°S that is a cap 29° in radius centred on the north celestial pole, which is 6.3% of the whole celestial sphere. Nothing about the calendar or the aperture changes that — the cap is below the horizon at every hour of every night. Its mirror image, the same 6.3% around the south celestial pole, is circumpolar here and never goes down.
How many hours of true darkness does Las Campanas Observatory get?
10 hours 53 minutes on the best night, around 21 June, falling to 6 hours 50 minutes around 21 December. The measure is astronomical darkness — the Sun a full eighteen degrees under — not simply the hours between sunset and sunrise. Every night of the year gets there eventually, which is the quiet advantage of not being any further from the equator than this.
When is the Milky Way best from Las Campanas Observatory?
June and July, and the timing is the whole point. The core transits at midnight around 17 June everywhere, but at 29.0°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 Las Campanas Observatory from the other sites on this map?
The nearest is La Silla Observatory, about 27 km to the south. That is also the nearest other observatory, with the next one 129 km beyond it. These are straight-line distances over the surface, not driving distances, and in this part of the world the two can differ considerably.