Glacier National Park

The southern sky is open here. The land to the south rises no more than 5.7 degrees, and the Milky Way core reaches 12.3, so it clears the ground by about 6.6 degrees at its highest.

Computed from elevation data, 16 directions sampled out to 19 miles and corrected for the curve of the Earth. Site elevation 4,501 feet, worst southern angle 5.7 degrees. ⚠️ This is arithmetic, not a visit. It knows the shape of the land and nothing about a locked gate, a security light or where a car can actually stop. The nearest sample sits 820 feet out, so a treeline at the edge of a clearing does not register in it at all, and at a wooded site that is the thing most likely to be wrong.

Finding a spot. No individual pullout is named here. What decides a good one is a clear view low to the south, because the Milky Way core and most of the season's best targets sit low in the southern sky. From this latitude the core never climbs higher than about 12 degrees, roughly a fist and a half held at arm's length above the horizon, so a ridge or a treeline to the south takes it away entirely. An ordinary parking area with an open southern horizon beats a named viewpoint with a ridge in the way.

Two other things matter as much and are easier to judge on arrival: whether headlights sweep the spot as cars pass, and whether there is a light left on somewhere that no map records. Local knowledge is welcome from anyone who knows a place well.

Glacier and Waterton Lakes across the border are certified together as an International Dark Sky Park, in the Park Service's own words. Its nightly astronomy programs are usually offered in July and August, again in its words, at St. Mary and at Apgar on the west side, with a 20-inch telescope at the Dusty Star Observatory at the St. Mary Visitor Center, and Logan Pass star parties happen on announced dates with tickets, because parking there is limited. That is the Park Service describing its own programs, not a visit by anyone from this site.

How dark is it? Not measured. Nobody has published a sky-brightness reading for the visitor center that this site can point at. What the Park Service says is that light pollution's effects are evident even in Glacier's protected skies, that it monitors light pollution over the park in support of the certification, and that its own monitoring image shows lights from businesses half a mile outside the park and the visitor center's own light.

Not known:

• Which spot to stand in: nowhere is pinned, because nobody from this site has been there. The visitor center is where the Park Service runs its programs, not a recommendation from anyone who has looked at the sky from it
• Where a car can stop after the visitor center closes, and whether it can stay the night
• Whether lights on the building or in the parking area stay on after the programs end
• Cell coverage at the visitor center
• What the parking area's own horizon looks like, as opposed to the computed terrain