Places · Dark sky
Cherry Springs State Park
A field on a Pennsylvania plateau that draws hundreds of telescopes on a clear new-moon weekend, and one of the few genuinely dark sites within reach of the American northeast.
- Where
- Pennsylvania, United States
- Coordinates
- 41.66°N 77.82°W
- Since
- 2008
- On the map
- Show me
- More
- dcnr.pa.gov
The sky from here
The sky over this spot is zone 3 — rural transition, Bortle 3–4, with a naked-eye limit around magnitude 6.2–7.0. The Milky Way is clearly there but loses its detail near the horizon. Light domes are obvious in several directions.
Against that sky 106 of the 110 Messier objects are straightforward in 10×50 binoculars and 106 in a 130mm, with 38 reachable by eye alone. The nearest sky of Bortle 2 or better lies about 316 km north-east 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.
The centre of the galaxy only ever reaches 19° above the horizon from here, so the richest part of the Milky Way is always seen through the thickest air. It is the single biggest difference between this sky and one further south. Of the 110 Messier objects, 12 never set from here and every one of them rises at some point in the year.
The sky here is kindest to Sunflower Galaxy, Andromeda Galaxy and Cat's 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.
Little Dumbbell, Pinwheel Galaxy and Owl Nebula 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 41.66°N 77.82°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 Cherry Springs State Park?
Everything south of declination −48°. From 41.7°N that is a cap 42° in radius centred on the south celestial pole, which is 13% 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 Cherry Springs State Park get?
From about 4 hours 26 minutes at the thin end of the year, near 21 June, up to 11 hours 30 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 Cherry Springs State Park?
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. 41.7°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 Cherry Springs State Park from the other sites on this map?
Its closest neighbour on this map is Space Telescope Science Institute, 278 km away to the south. The nearest other dark sky is Mont-Mégantic, 682 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.