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Palomar Observatory
The 200-inch Hale Telescope was the largest in the world for 45 years. The Zwicky Transient Facility now sweeps the same sky nightly for anything that flares.
- Where
- California, United States
- Coordinates
- 33.36°N 116.86°W
- Since
- 1949
- On the map
- Show me
The sky from here
This is a zone 4 sky — suburban edge on the nine-grade scale, Bortle 4–5, reaching roughly magnitude 5.7–6.5 unaided. The Milky Way is a faint band overhead and gone lower down. The sky is noticeably grey rather than black.
That grade puts 99 of the catalogue within easy reach of 10×50 binoculars and 100 within a 130mm — 21 of them need no instrument at all. Genuinely dark sky — zone 2 or darker — starts about 118 km north-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 28° 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, 5 never set from here and every one of them rises at some point in the year.
Of everything in the catalogue, Ring Nebula, Triangulum Galaxy and Hercules Cluster 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.
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 33.36°N 116.86°W. 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 Palomar Observatory?
Everything south of declination −57°. From 33.4°N that is a cap 33° in radius centred on the south celestial pole, which is 8.2% 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 north celestial pole is the compensation, and it never sets.
How many hours of true darkness does Palomar Observatory get?
From about 6 hours 12 minutes at the thin end of the year, near 21 June, up to 11 hours 6 minutes around 21 December. 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 Palomar Observatory?
Mid-June at its highest, with a workable season either side of it running from about May into September. Because 33.4°N keeps full astronomical darkness all year, the whole of that season is usable, which is not the case for observers much further from the equator, who lose the peak of it to summer twilight.
How far is Palomar Observatory from the other sites on this map?
Its closest neighbour on this map is Mount Wilson Observatory, 147 km away to the north-west. That is also the nearest other observatory, with the next one 517 km beyond it. Measured as the great circle between coordinates, which is the shortest path across the surface and rarely the one you could travel.