Milky Way season, park by park

What this guide is for

This guide ranks national park units by how good their best month is for seeing the Milky Way core, and gives each park its own best dates. Each score counts the dark hours when the core is above the horizon and the Moon isn't, then reduces it by the typical cloud over the park. The method is explained at the end of this page, and each park page repeats the inputs for its own location.

Beyond the Milky Way

The core is only one thing overhead. For events with fixed dates, see the sky calendar, which covers eclipses, planets and meteor showers. For what the galaxy is made of and what we still don't know about it, start with the mysteries section.

The top six

Every park, ranked

Darkest and brightest skies

Separate from the core score, the Park Service has modelled how much artificial light brightens the sky over the lower 48. Lower numbers are darker.

Darkest five

• Big Bend National Park: ratio 0.011
• Yellowstone National Park: ratio 0.016
• Great Basin National Park: ratio 0.02
• Capitol Reef National Park: ratio 0.029
• Canyonlands National Park: ratio 0.036

Brightest five

• Gateway Arch National Park: ratio 60.991
• Cuyahoga Valley National Park: ratio 21.352
• Indiana Dunes National Park: ratio 16.208
• Saguaro National Park: ratio 12.415
• Hot Springs National Park: ratio 7.367

The ratio compares artificial sky brightness with the natural brightness of a moonless sky. 47 parks are covered. Hawaii, American Samoa, the Virgin Islands and a few offshore parks have no value in the model. Source: National Park Service, read at each park's reference point.

Eight of Alaska's national parks aren't in the table, because from there the core never gets high enough to see. Why, and what you can see instead.

How the core score works

The score runs from 0 to 100. For each month it takes the best seven nights and averages the hours when the galactic core is more than 10 degrees above the horizon, the Sun is more than 18 degrees below it and the Moon is below the horizon. It caps that at four hours, then multiplies by the share of the month the park isn't under cloud on average. A score of 0 means the core can't be seen that month, or the Moon is up whenever it is.

The positions of the Sun, Moon and core are calculated from published formulas and checked against known moon phases and equinoxes. Cloud is a monthly NASA satellite average from 2001 to 2025 for a grid cell roughly 100 km across, covering day and night. The score doesn't include local weather, smoke, haze, light from nearby towns. The modelled sky glow figures are shown separately. It ranks months and parks. It isn't a forecast for any night.

The core is the brightest part of the Milky Way. The fainter band through Cygnus and Cassiopeia is high in the evening sky from late summer into autumn, when the core is out of reach.