The core clears 10 degrees during full darkness on most nights from March to August. In January, February, September, 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 | 75% |
| February | 0 | Core not visible | 0 | 68% |
| March | 1 | March 11 to 17 | 0.1 | 70% |
| April | 8 | April 7 to 13 | 0.9 | 65% |
| May | 15 | May 4 to 10 | 1.6 | 61% |
| June | 29 | June 1 to 7 | 2.4 | 51% |
| July | 37 | July 1 to 7 | 2.1 | 29% |
| August | 19 | August 1 to 7 | 1.1 | 32% |
| September | 4 | September 1 to 7 | 0.3 | 41% |
| October | 0 | Core not visible | 0 | 58% |
| November | 0 | Core not visible | 0 | 71% |
| December | 0 | Core not visible | 0 | 74% |
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 5 is the best night. The core is above 10 degrees and the moon is down from 12:06 am to 2:26 am, with the moon 3% lit that night.
- July: July 1 is the best night. The core is above 10 degrees and the moon is down from 11:56 pm to 1:56 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 10:56 pm to 11:56 pm, with the moon 0% lit that night.
Clock times are Pacific time with daylight saving applied. The best nights fall around the new moon, so the dates shift by about 11 days each year.
About Mount Rainier National Park
Mount Rainier is a huge glacier-covered volcano that dominates the horizon south of Seattle, rising to 14,410 feet. Below the ice are meadows that bloom with wildflowers in July and August. The Wonderland Trail circles the whole mountain, about 93 miles.
Rainier became a national park in 1899, one of the first handful in the country. Indigenous peoples including the Puyallup, Nisqually and Yakama have long used the mountain, which they know by other names. It's still an active volcano.
Mount Rainier National Park is a national park in Washington. The National Park Service places its center at 46.86 degrees north and 121.70 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 Mount Rainier National Park compares
Its best monthly core score of 37 ranks 46 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 Mount Rainier National Park runs from 29% in July to 75% in January.
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 Mount Rainier National Park, it puts the added glow at about 75% of the natural brightness of a moonless sky (a ratio of 0.751). That makes it 31st 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 Mount Rainier 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 Mount Rainier National Park all year?
The core clears 10 degrees during full darkness on most nights from March to August. In January, February, September, 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 Mount Rainier National Park?
The Park Service models how much artificial light brightens the sky across the lower 48. At the point used for Mount Rainier National Park, it puts the added glow at about 75% of the natural brightness of a moonless sky (a ratio of 0.751). That makes it 31st 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 Mount Rainier 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 11:56 pm to 1:56 am.
