The core clears 10 degrees during full darkness on most nights from February to October. In January, 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 | 62% |
| February | 3 | February 10 to 16 | 0.3 | 65% |
| March | 13 | March 10 to 16 | 1.4 | 63% |
| April | 27 | April 6 to 12 | 2.5 | 57% |
| May | 35 | May 3 to 9 | 3.5 | 60% |
| June | 50 | June 1 to 7 | 4.7 | 50% |
| July | 53 | July 1 to 7 | 4.5 | 47% |
| August | 38 | August 1 to 7 | 2.9 | 47% |
| September | 18 | September 1 to 7 | 1.3 | 42% |
| October | 5 | October 1 to 7 | 0.4 | 50% |
| November | 0 | Core not visible | 0 | 54% |
| December | 0 | Core not visible | 0 | 64% |
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 10:50 pm to 3:40 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 10:30 pm to 3:10 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 10:00 pm to 1:00 am, with the moon 0% lit that night.
Clock times are Central time with daylight saving applied. The best nights fall around the new moon, so the dates shift by about 11 days each year.
About Gateway Arch National Park
Gateway Arch is the smallest national park in the country, a patch of riverfront in St. Louis, Missouri, centered on a shining stainless steel arch that stands 630 feet tall. A tram runs up inside each leg to a small window room at the top. The Old Courthouse nearby is where the Dred Scott case was first heard.
The memorial was authorized in 1935 to honor the city's role in westward expansion. Eero Saarinen won the design contest, and the arch was finished in 1965. Congress renamed the site Gateway Arch National Park in 2018.
Gateway Arch National Park is a national park in Missouri. The National Park Service places its center at 38.63 degrees north and 90.19 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 Gateway Arch National Park compares
Its best monthly core score of 53 ranks 27 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 Gateway Arch National Park runs from 42% in September to 65% in February.
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 Gateway Arch National Park, it puts the added glow at about 61.0 times the natural brightness of a moonless sky (a ratio of 60.991). That makes it the brightest 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 Gateway Arch 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 Gateway Arch National Park all year?
The core clears 10 degrees during full darkness on most nights from February to October. In January, 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 Gateway Arch National Park?
The Park Service models how much artificial light brightens the sky across the lower 48. At the point used for Gateway Arch National Park, it puts the added glow at about 61.0 times the natural brightness of a moonless sky (a ratio of 60.991). That makes it the brightest 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 Gateway Arch 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 10:30 pm to 3:10 am.
