Places · Observatory
La Silla Observatory
ESO's first site, and still the home of HARPS — the spectrograph that turned exoplanet detection from a handful of discoveries into a catalogue.
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 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.
Of everything in the catalogue, Southern Pinwheel, Butterfly Cluster and Lagoon Nebula 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 29.26°S 70.73°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 La Silla Observatory?
Everything north of declination +61°. From 29.3°S that is a cap 29° in radius centred on the north celestial pole, which is 6.4% of the whole celestial sphere. It is out of reach permanently rather than seasonally: no time of year and no instrument brings it above the horizon. The matching 6.4% around the south celestial pole is the same geometry inverted, and never sets.
How many hours of true darkness does La Silla Observatory get?
10 hours 54 minutes on the best night, around 21 June, falling to 6 hours 48 minutes around 21 December. That counts only proper astronomical night, with the Sun eighteen degrees down; the merely-dark hours either side of it are longer. 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 La Silla Observatory?
June and July, and the timing is the whole point. The core transits at midnight around 17 June everywhere, but at 29.3°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 La Silla Observatory from the other sites on this map?
Las Campanas Observatory is the nearest thing to it here — 27 km to the north. That is also the nearest other observatory, with the next one 102 km beyond it. Measured as the great circle between coordinates, which is the shortest path across the surface and rarely the one you could travel.