AAS Nova
Places · Observatory
KAGRA
Built inside a mountain and cooled to 20 K — underground to escape ground motion, cryogenic to escape thermal noise in the mirrors.
- Where
- Kamioka, Japan
- Coordinates
- 36.41°N 137.31°E
- Since
- 2020
- 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 89 km north.
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 25° 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, 9 never set from here and every one of them rises at some point in the year.
Of everything in the catalogue, Hercules Cluster, Ring Nebula and Cat's Eye 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 36.41°N 137.31°E. Darkness is estimated rather than measured; everything else follows from the latitude and holds along the whole parallel. How accurate this is.
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Questions
What part of the sky never rises at KAGRA?
Everything south of declination −54°. From 36.4°N that is a cap 36° in radius centred on the south celestial pole, which is 9.8% 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 9.8% around the north celestial pole, is circumpolar here and never goes down.
How many hours of true darkness does KAGRA get?
Between 5 hours 39 minutes on the shortest night of the year, around 21 June, and 11 hours 15 minutes on the longest, around 21 December. That counts only proper astronomical night, with the Sun eighteen degrees down; the merely-dark hours either side of it are longer. The sky here reaches it on every night of the year, which is not true much further from the equator.
When is the Milky Way best from KAGRA?
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. 36.4°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 KAGRA from the other sites on this map?
The nearest is Uchinoura Space Center, about 812 km to the south-west. The nearest other observatory is FAST — the Five-hundred-metre dish, 3,120 km to the west. Distances are great-circle, so they are what a signal covers rather than what a road does.