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 | 68% |
| February | 3 | February 10 to 16 | 0.4 | 70% |
| March | 14 | March 10 to 16 | 1.6 | 64% |
| April | 28 | April 6 to 12 | 2.7 | 59% |
| May | 35 | May 3 to 9 | 3.7 | 62% |
| June | 48 | June 1 to 7 | 5.0 | 52% |
| July | 47 | July 1 to 7 | 4.7 | 53% |
| August | 39 | August 1 to 7 | 3.1 | 50% |
| September | 19 | September 21 to 27 | 1.4 | 46% |
| October | 5 | October 1 to 7 | 0.4 | 51% |
| November | 0 | Core not visible | 0 | 55% |
| December | 0 | Core not visible | 0 | 68% |
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 2 is the best night. The core is above 10 degrees and the moon is down from 10:34 pm to 3:34 am, with the moon 4% lit that night.
- July: July 1 is the best night. The core is above 10 degrees and the moon is down from 10:04 pm to 2:54 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 9:34 pm to 12:54 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 Mammoth Cave National Park
Mammoth Cave in Kentucky is the longest known cave system in the world, with more than 400 miles mapped, and explorers are still finding new passages. Tours range from easy strolls to crawls through tight spots. Above ground, the Green River winds through quiet forest.
People have used the cave for thousands of years, and in the 1800s it became a tourist attraction with enslaved guides such as Stephen Bishop who mapped it. The park was authorized in 1926 and officially established in 1941.
Mammoth Cave National Park is a national park in Kentucky. The National Park Service places its center at 37.20 degrees north and 86.13 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 Mammoth Cave National Park compares
Its best monthly core score of 48 ranks 38 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 Mammoth Cave National Park runs from 46% in September to 70% 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 Mammoth Cave National Park, it puts the added glow at about 1.8 times the natural brightness of a moonless sky (a ratio of 1.82). That makes it 40th 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 Mammoth Cave National Park?
June, July and August are the best months. The best week of 2027 is June 1 to 7.
Can you see the Milky Way at Mammoth Cave 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 Mammoth Cave National Park?
The Park Service models how much artificial light brightens the sky across the lower 48. At the point used for Mammoth Cave National Park, it puts the added glow at about 1.8 times the natural brightness of a moonless sky (a ratio of 1.82). That makes it 40th 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 Mammoth Cave National Park?
Yes. A bright moon hides the Milky Way. The best night in June is June 2, when the moon is 4% lit and the core is above 10 degrees from 10:34 pm to 3:34 am.
