The core clears 10 degrees during full darkness on most nights from March to September. In January, February, October, November and December it's out of reach, either too close to the Sun or too low in the dark.
Core score by month
| Month | Core score | Best week | Moon-free core hours a night | Average cloud |
|---|---|---|---|---|
| January | 0 | Core not visible | 0 | 67% |
| February | 0 | No moon-free core hours | 0 | 70% |
| March | 5 | March 10 to 16 | 0.7 | 70% |
| April | 12 | April 7 to 13 | 1.6 | 69% |
| May | 19 | May 4 to 10 | 2.4 | 69% |
| June | 41 | June 1 to 7 | 3.5 | 53% |
| July | 50 | July 1 to 7 | 3.3 | 38% |
| August | 29 | August 1 to 7 | 2.0 | 42% |
| September | 10 | September 1 to 7 | 0.7 | 44% |
| October | 1 | October 1 to 7 | 0.1 | 58% |
| November | 0 | Core not visible | 0 | 66% |
| December | 0 | Core not visible | 0 | 71% |
Times are for the best seven nights in each month. Moon-free means the moon is below the horizon. The core counts as visible above 10 degrees in full darkness, when the Sun is more than 18 degrees below the horizon.
The best nights in 2027
- June: June 4 is the best night. The core is above 10 degrees and the moon is down from 11:52 pm to 3:22 am, with the moon 0% lit that night.
- July: July 1 is the best night. The core is above 10 degrees and the moon is down from 11:32 pm to 2:52 am, with the moon 5% lit that night.
- August: August 1 is the best night. The core is above 10 degrees and the moon is down from 10:52 pm to 12:52 am, with the moon 0% lit that night.
Clock times are Mountain time with daylight saving applied. The best nights fall around the new moon, so the dates shift by about 11 days each year.
About Grand Teton National Park
The Teton Range rises almost straight out of the Jackson Hole valley in Wyoming, with no foothills to soften the view. Climbers come for the peaks, and everyone else comes for the lakes, moose and sunrise on Mormon Row. The skyline is one of the best known in the American West.
The park was created in 1929, but it only protected the mountains. Land that John D. Rockefeller Jr. bought quietly in the valley, together with the old Jackson Hole National Monument, was added in 1950 after a long political fight.
Grand Teton National Park is a national park in Wyoming. The National Park Service places its center at 43.82 degrees north and 110.71 degrees west, and the sky calculations on this page use that point. Visitor information, fees and alerts are on the park's own page. National Park Service (opens in a new tab).
How Grand Teton National Park compares
Its best monthly core score of 50 ranks 32 of 54 national park units that can see the core. The highest is Lassen Volcanic National Park at 86, and the lowest is Voyageurs National Park at 13. Cloud at Grand Teton National Park runs from 38% in July to 71% in December.
The score ranks months and parks. It isn't a forecast for any night, and it leaves out local weather, smoke and light from nearby towns. How the core score works.
How dark is the sky?
The Park Service models how much artificial light brightens the sky across the lower 48. At the point used for Grand Teton National Park, it puts the added glow at about 4% of the natural brightness of a moonless sky (a ratio of 0.043). That makes it 6th darkest of the 47 parks it covers. Lower is darker. This is a model, not a reading taken at the park, and it describes one point, so the edges of a large park can differ.
Questions people ask
When is the best time to see the Milky Way at Grand Teton National Park?
June, July and August are the best months. The best week of 2027 is July 1 to 7.
Can you see the Milky Way at Grand Teton National Park all year?
The core clears 10 degrees during full darkness on most nights from March to September. In January, February, October, November and December it's out of reach, either too close to the Sun or too low in the dark.
How dark is the sky at Grand Teton National Park?
The Park Service models how much artificial light brightens the sky across the lower 48. At the point used for Grand Teton National Park, it puts the added glow at about 4% of the natural brightness of a moonless sky (a ratio of 0.043). That makes it 6th darkest of the 47 parks it covers. Lower is darker. This is a model, not a reading taken at the park, and it describes one point, so the edges of a large park can differ.
Does the moon matter at Grand Teton National Park?
Yes. A bright moon hides the Milky Way. The best night in July is July 1, when the moon is 5% lit and the core is above 10 degrees from 11:32 pm to 2:52 am.
A lab for better lighting
Grand Teton treats its night sky as a research subject. A 2023 survey found that 83 percent of respondents said night sky viewing was an important part of their visit. The park's Sensory Lab has run experiments on how artificial light affects bats and nocturnal insects, and the park has six dominant bat species.
The experiments are real lighting. In 2019 the park put experimental LEDs in the 32 streetlamps of the Colter Bay parking area. In 2023 it placed thirteen temporary luminaries in previously unlit areas from July 1 to September 14, cycling through four colors plus a dark control. Visitors preferred the lowest intensity (86 percent), and the single most popular choice was the lowest-intensity red setting, at 37 percent.
Why it matters
The Park Service puts the larger problem in one line: artificial light unnaturally brightens the night by ten percent each year. That's why a park with a famous skyline cares about a parking lot. Next door, Yellowstone is working on its own fixtures, and Glacier worked through a lighting retrofit for its dark sky designation.
How it fits our numbers
In our 2027 numbers, Grand Teton peaks in July with a core score of 50 out of 100. The best week is July 1 to 7, with about 3.3 moon-free hours a night and average cloud near 38 percent. The park's lighting experiments are aimed at keeping that sky intact for the people who come to see it.
