Places · Observatory
Green Bank Telescope
The largest fully steerable dish on Earth, 100 m across, inside a radio quiet zone where mobile phones and microwave ovens are restricted by law.
- Where
- West Virginia, United States
- Coordinates
- 38.43°N 79.84°W
- Since
- 2000
- On the map
- Show me
The sky from here
This is a zone 3 sky — rural transition on the nine-grade scale, Bortle 3–4, reaching roughly magnitude 6.2–7.0 unaided. The Milky Way is clearly there but loses its detail near the horizon. Light domes are obvious in several directions.
That grade puts 106 of the catalogue within easy reach of 10×50 binoculars and 106 within a 130mm — 38 of them need no instrument at all. Genuinely dark sky — zone 2 or darker — starts about 403 km east.
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.
The centre of the galaxy reaches 23° at its highest, which puts the brightest part of the Milky Way clear of the horizon murk without ever being overhead. Of the 110 Messier objects, 10 never set from here and every one of them rises at some point in the year.
Of everything in the catalogue, Hercules Cluster, Cat's Eye Galaxy and Andromeda Galaxy 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.
Pinwheel Galaxy, Owl Nebula and Spindle Galaxy never set from this latitude, so they are available on any clear night of the year rather than for one season of it.
Read at 38.43°N 79.84°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 Green Bank Telescope?
Everything south of declination −52°. From 38.4°N that is a cap 38° in radius centred on the south celestial pole, which is 11% 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 11% around the north celestial pole is the same geometry inverted, and never sets.
How many hours of true darkness does Green Bank Telescope get?
11 hours 21 minutes on the best night, around 21 December, falling to 5 hours 14 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 Green Bank Telescope?
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. 38.4°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 Green Bank Telescope from the other sites on this map?
Space Telescope Science Institute is the nearest thing to it here — 296 km to the east. The nearest other observatory is LIGO Livingston, 1,330 km to the south-west. These are straight-line distances over the surface, not driving distances, and in this part of the world the two can differ considerably.