Places · Observatory
Pierre Auger Observatory
Sixteen hundred water tanks spread over 3,000 km² of pampas, waiting for the air shower of a cosmic ray carrying the energy of a well-hit tennis ball.
The sky from here
Measured at these coordinates the sky is zone 2: rural, which is Bortle 2–3 and a naked-eye limit of about 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.
Of the 110 Messier objects, 44 are an unaided-eye target from a sky this dark, 107 are comfortable in 10×50s and 107 in a 130mm reflector. There is nowhere darker worth driving to; this is already among the better skies on the planet.
Every night of the year reaches full astronomical darkness at this latitude; the Sun always gets its eighteen degrees below the horizon, which places much further from the equator cannot say.
The centre of the galaxy climbs to 84° at its best — high enough that the summer Milky Way is genuinely three-dimensional rather than a band low in the south. Of the 110 Messier objects, none are circumpolar and 8 never rise.
Ptolemy's Cluster, Butterfly Cluster and Southern Pinwheel pass close to the zenith from this latitude — 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, Owl Nebula, Spindle Galaxy and Bode's Galaxy never clear the horizon here at all. No amount of aperture or patience changes that; the only remedy is to travel.
Read at 35.21°S 69.32°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 Pierre Auger Observatory?
Everything north of declination +55°. From 35.2°S that is a cap 35° in radius centred on the north celestial pole, which is 9.1% 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 9.1% around the south celestial pole is the same geometry inverted, and never sets.
How many hours of true darkness does Pierre Auger Observatory get?
11 hours 11 minutes on the best night, around 21 June, falling to 5 hours 53 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 Pierre Auger Observatory?
June and July, and the timing is the whole point. The core transits at midnight around 17 June everywhere, but at 35.2°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 Pierre Auger Observatory from the other sites on this map?
Vera C. Rubin Observatory is the nearest thing to it here — 568 km to the north. That is also the nearest other observatory, with the next one 568 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.