Places · Observatory
Extremely Large Telescope
A 39 m segmented mirror under construction on a levelled peak next door to Paranal. When it opens it will be the largest optical telescope ever built, by a wide margin.
- Where
- Cerro Armazones, Chile
- Coordinates
- 24.59°S 70.19°W
- Since
- 2028
- On the map
- Show me
- More
- elt.eso.org
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.
At its highest the galactic centre stands 86° 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 2 never rise.
Lagoon Nebula, Trifid Nebula 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, 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 24.59°S 70.19°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 Extremely Large Telescope?
Everything north of declination +65°. From 24.6°S that is a cap 25° in radius centred on the north celestial pole, which is 4.5% 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 Extremely Large Telescope get?
From about 7 hours 23 minutes at the thin end of the year, near 21 December, up to 10 hours 41 minutes around 21 June. The measure is astronomical darkness — the Sun a full eighteen degrees under — not simply the hours between sunset and sunrise. Unlike sites further from the equator, no part of the year here is written off entirely.
When is the Milky Way best from Extremely Large Telescope?
June and July, and the timing is the whole point. The core transits at midnight around 17 June everywhere, but at 24.6°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 Extremely Large Telescope from the other sites on this map?
Its closest neighbour on this map is Paranal Observatory — the VLT, 22 km away to the west. That is also the nearest other observatory, with the next one 303 km beyond it. Distances are great-circle, so they are what a signal covers rather than what a road does.