How dark is the sky at Antelope Island State Park?

Modelled zenith brightness from the 2024 World Atlas of Artificial Night Sky Brightness puts Antelope Island State Park at about 20.85 mag/arcsec², roughly Bortle class 4. That is an approximation derived from satellite data, not a field measurement; it is certified by DarkSky International as an International Dark Sky Park.

When is the next moon-free dark window at Antelope Island State Park?

The next stretch of essentially moon-free dark hours runs Nov 2–15 (14 nights), computed from Moon phase and altitude with Skyfield and JPL DE440s. Cloud cannot be known that far ahead; the live seven-night forecast on this page shows real cloud cover once a window is close.

What is the clearest month at Antelope Island State Park?

Over 2021–2025, September (89%), August (85%), July (84%) had the highest share of nights with astronomical darkness that stayed clear (weighted cloud cover ≤ 20%); across the year it was 62%. ERA5 reanalysis via Open-Meteo — historical frequency, not a forecast.

United States · International Dark Sky Park

Stargazing at Antelope Island State Park

How dark this certified sky really is, how far it is from the nearest cities, a live seven-night forecast for the site itself, and the moon-free nights worth planning around. Official DarkSky International page ↗

Sky at the siteBortle ≈ 420.85 mag/arcsec² · 2024 atlas

From Salt Lake City~48 min34.5 km straight-line · head north-west · estimated

Next moon-free windowNov 2–1514 nights · moon geometry only

How dark the sky really is at Antelope Island State Park

Modelled zenith brightness at the site's coordinates is 20.85 mag/arcsec², which maps to roughly Bortle 4 (what each level means). This is an approximation from the 2024 light-pollution atlas, not a field measurement — and it describes the single point DarkSky lists, not the darkest corner of the park.

Rural-to-suburban transition: the Milky Way is clearly visible on clear, moonless nights, though light domes from nearby towns sit on parts of the horizon. Certification here is as much about the international dark sky park's lighting policy and public programmes as about raw darkness — aim your observing away from the brighter horizon.

Getting to Antelope Island State Park

The nearest cities we publish guides for, with the direction to head and a rough drive estimate.

From Salt Lake City
head north-west · 34.5 km straight-line · ≈44.9 km by road · ≈48 min · reachable tonight
From Las Vegas
head north-east · 590 km straight-line · ≈767 km by road · ≈8.5 h · weekend trip
From Denver
head west · 626.2 km straight-line · ≈814.1 km by road · ≈9 h · weekend trip

Estimated from straight-line distance x a 1.3 road-detour factor and staged average speeds (40 km/h leaving town, 70 km/h regional, 95 km/h highway). It is a rough guide, not a routed drive time.

The next seven nights at Antelope Island State Park

Loading the live forecast…

Plan the next 90 days at Antelope Island State Park

Moon-free dark windows are astronomy — computable years ahead. Cloud is not: beyond the 16-night forecast nobody knows the weather, and we won't pretend to. What five years of reanalysis can say is how often each month's nights actually stayed clear here.

Nov 2–1514 moon-free nights55% of November nights here stayed clear (2021–2025)
Dec 2–1413 moon-free nights23% of December nights here stayed clear (2021–2025)
Dec 31 – Jan 1314 moon-free nights23% of December nights here stayed clear (2021–2025)

Clear nights by month, 2021–2025

Jan41%
Feb46%
Mar43%
Apr60%
May72%
Jun81%
Jul84%
Aug85%
Sep89%
Oct67%
Nov55%
Dec23%

Clearest months historically: September (89%), August (85%), July (84%); across the year 62% of nights with astronomical darkness stayed clear.

"Clear" = weighted cloud cover (low 0.5 / mid 0.3 / high 0.2) ≤ 20% across the night's astronomical darkness. ERA5 reanalysis via Open-Meteo Archive, 2021–2025 (CC BY 4.0) — historical frequency, not a forecast. Once a window comes within 16 nights, the live forecast above takes over.

Put Antelope Island State Park's dark-sky nights on your calendar

Every month has a stretch of nights when the Moon leaves the dark hours at Antelope Island State Park essentially moon-free. Subscribe once and each window lands in your own calendar, about a year ahead — no account, no email.

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moon & darkness geometry only — cloud can't be known this far out; check the live forecast above when a window gets close

Questions people ask about Antelope Island State Park

How dark is the sky at Antelope Island State Park?: Modelled zenith brightness from the 2024 World Atlas of Artificial Night Sky Brightness puts Antelope Island State Park at about 20.85 mag/arcsec², roughly Bortle class 4. That is an approximation derived from satellite data, not a field measurement; it is certified by DarkSky International as an International Dark Sky Park.
How far is Antelope Island State Park from Salt Lake City?: About 34.5 km in a straight line, heading north-west from Salt Lake City. Using a 1.3 road-detour factor and staged average speeds that is roughly 44.9 km and 48 min of driving — an estimate, not a routed drive time.
When is the next moon-free dark window at Antelope Island State Park?: The next stretch of essentially moon-free dark hours runs Nov 2–15 (14 nights), computed from Moon phase and altitude with Skyfield and JPL DE440s. Cloud cannot be known that far ahead; the live seven-night forecast on this page shows real cloud cover once a window is close.
What is the clearest month at Antelope Island State Park?: Over 2021–2025, September (89%), August (85%), July (84%) had the highest share of nights with astronomical darkness that stayed clear (weighted cloud cover ≤ 20%); across the year it was 62%. ERA5 reanalysis via Open-Meteo — historical frequency, not a forecast.

Place name and coordinates: DarkSky International (reviewed 2026-07-15, data 2026-10-13). Light pollution: David Lorenz, World Atlas 2024 (EOG VIIRS, CC BY 4.0), approximate. Cloud: Open-Meteo.com (CC BY 4.0). Moon and darkness geometry: Skyfield + JPL DE440s, computed locally. Drive times are estimates, not routes.