Places · Observatory
FAST — the Five-hundred-metre dish
The largest filled-aperture radio telescope in the world, its 500 m reflector actively reshaped by 2,225 winches under the surface. It has found over a thousand pulsars.
- Where
- Guizhou, China
- Coordinates
- 25.65°N 106.86°E
- Since
- 2016
- On the map
- Show me
- More
- fast.bao.ac.cn
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 reaches 35° 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, 2 never set from here and every one of them rises at some point in the year.
Pleiades, Dumbbell Nebula and Crab Nebula 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.
Bode's Galaxy and Cigar 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 25.65°N 106.86°E. 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 FAST?
Everything south of declination −64°. From 25.7°N that is a cap 26° in radius centred on the south celestial pole, which is 4.9% of the whole celestial sphere. Nothing about the calendar or the aperture changes that — the cap is below the horizon at every hour of every night. Its mirror image, the same 4.9% around the north celestial pole, is circumpolar here and never goes down.
How many hours of true darkness does FAST get?
10 hours 44 minutes on the best night, around 21 December, falling to 7 hours 15 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 FAST?
From roughly May to September, peaking around 17 June when the core is on the meridian at midnight and drifting into the evening sky thereafter. The useful thing about 25.7°N is that every one of those nights actually gets dark — at higher latitudes the best weeks of the core season are also the weeks with no astronomical night at all.
How far is FAST from the other sites on this map?
Xichang Satellite Launch Center is the nearest thing to it here — 559 km to the north-west. The nearest other observatory is KAGRA, 3,120 km to the north-east. Measured as the great circle between coordinates, which is the shortest path across the surface and rarely the one you could travel.