Places · Observatory
Arecibo Observatory (collapsed)
A 305 m dish slung in a limestone sinkhole for 57 years. Cables failed in 2020 and the platform fell into the bowl; the site is not being rebuilt.
The sky from here
The sky over this spot is zone 6 — bright suburban, Bortle 6–7, with a naked-eye limit around magnitude 4.7–5.5. The sky within thirty degrees of the horizon glows greyish white. Only the brighter constellations survive.
Against that sky 37 of the 110 Messier objects are straightforward in 10×50 binoculars and 37 in a 130mm, with 9 reachable by eye alone. The nearest sky of Bortle 2 or better lies about 52 km north of here.
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 43° 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 every one of them rises at some point in the year.
The sky here is kindest to Beehive Cluster, Phantom Galaxy and Black Eye Galaxy, 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.
Read at 18.34°N 66.75°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 Arecibo Observatory (collapsed)?
Everything south of declination −72°. From 18.3°N that is a cap 18° in radius centred on the south celestial pole, which is 2.5% 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 2.5% around the north celestial pole is the same geometry inverted, and never sets.
How many hours of true darkness does Arecibo Observatory (collapsed) get?
10 hours 23 minutes on the best night, around 21 December, falling to 8 hours 1 minutes around 21 June. 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 Arecibo Observatory (collapsed)?
Around 17 June, when the galactic centre transits at local midnight, and usefully from about May to September — earlier each evening as the season goes on. 18.3°N is close enough to the equator that the sky reaches full astronomical darkness on every night of the year, so unlike sites further north there is no part of the season where the core is high and the sky refuses to cooperate.
How far is Arecibo Observatory (collapsed) from the other sites on this map?
Landing Zones 1 & 2 is the nearest thing to it here — 1,800 km to the north-west. The nearest other observatory is Green Bank Telescope, 2,570 km to the north-west. Distances are great-circle, so they are what a signal covers rather than what a road does.