Arizona protects its night sky in one set of places and uses it in another

Twenty attractions in this database are there because of the darkness above them. Eight carry the International Dark Sky Park designation and twelve are working astronomical observatories. They sit in nine of Arizona’s fifteen counties, and only two counties hold both kinds.

The two groups also differ completely in whether anyone counts the people who arrive. All eight dark sky parks publish an official annual visitor figure. Not one of the twelve observatories does.

The eight designated parks

Grand Canyon National Park and Petrified Forest National Park hold the designation, as do three National Park Service monuments — Chiricahua in Cochise County, Tonto in Gila County and Pipe Spring in Mohave County — along with Tumacácori National Historical Park in Santa Cruz County and two units of the state park system, Kartchner Caverns in Cochise County and Oracle State Park in Pinal County.

Their 2024 visitor counts total 5,808,997. Grand Canyon accounts for 85 per cent of that on its own, which is the same distortion that appears in every Arizona figure it is included in; the other seven recorded 889,834 between them. The smallest is Oracle State Park at 13,002 and the second smallest Pipe Spring at 24,530.

The designation is one of the few this site’s ranking treats as adding significance, alongside World Heritage and National Historic Landmark status. It is worth being precise about what it adds: it records that a designating body has recognised the site’s night sky and its management, not that this database has measured how dark the sky is. No such measurement is held here.

The twelve observatories cluster on four mountains

Where the parks are scattered across seven counties, the observatories are concentrated in four, and within those counties they are concentrated further onto a handful of peaks.

Four are in Pima County, three of them on the same mountain: Kitt Peak National Observatory stands on the Tohono Oʼodham Nation 88 kilometres west-south-west of Tucson and holds more than twenty optical telescopes and two radio telescopes, among them the Nicholas U. Mayall Telescope, which was the second-largest telescope in the world at first light in 1973, and the McMath–Pierce solar telescope, which on completion in 1962 was the largest solar telescope and the largest unobstructed-aperture optical telescope anywhere. The fourth, Mount Lemmon Observatory, is in the Santa Catalina Mountains north-east of the city.

Three are on Mount Graham in Graham County, under the Mount Graham International Observatory: the Large Binocular Telescope, whose two 8.4-metre mirrors sit with their centres 14.4 metres apart at 10,700 feet, and the Submillimeter Telescope.

Three are around Flagstaff in Coconino County: Lowell Observatory, founded in 1894, a National Historic Landmark since 1965 and the place Pluto was identified in 1930; the Lowell Discovery Telescope, built at a dark site in the Coconino National Forest near Happy Jack at 7,740 feet; and the United States Naval Observatory Flagstaff Station, which is that institution’s national dark-sky observing facility.

Two are on Mount Hopkins in Santa Cruz County, where the Fred Lawrence Whipple Observatory is the Smithsonian Astrophysical Observatory’s largest field installation outside Cambridge, Massachusetts, and hosts VERITAS, an array of four 12-metre reflectors that observes gamma rays.

Why the two maps barely overlap

Only Coconino and Santa Cruz counties contain both a designated dark sky park and an observatory, and in neither case are they the same site.

The observatories are on mountains because altitude puts them above the thicker and more turbulent air; the designated parks are wherever the land was already protected for something else — a canyon, a cave, a mission, a fossil bed — and the dark sky is a second thing true of them. Arizona has both because it has a lot of high ground and a lot of federally managed land, but the two sets are answering different questions and were assembled by different institutions.

The counting asymmetry

The reason none of the twelve publishes a visitor count is not obscurity. Several run visitor centres and public programmes, and their readership is substantial: Kitt Peak’s Wikipedia article was read 32,075 times in 2024 and Lowell Observatory’s 31,112, placing them 47th and 51st of the 505 records whose readership is measured. Readership and visits are different measurements and this site does not convert one into the other, but a place read about tens of thousands of times is not one nobody has heard of.

It is that they are research institutions rather than visitor-serving agencies. The National Park Service and the Arizona State Parks system publish annual visitation because reporting it is part of what they are for. A telescope operated by a university department or a national laboratory has no equivalent obligation, so the number is not collected in a form anyone publishes.

This is the same pattern that appears elsewhere in the database, and it is the one most easily misread. An attraction with no published count is not a quiet one. The absence records which kind of body holds the land, and the methodology page sets out what the ranking does about it: missing measurements are dropped and the remaining weights renormalised, rather than a zero being entered on their behalf.