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Best time to see the Milky Way in Isle Royale National Park
May, June and July are the best months to see the Milky Way core at Isle Royale National Park. The odds stay modest even then: from 48.0 degrees north the core only climbs to 13 degrees above the southern horizon, and the park averages 70% cloud. The best week of 2027 is June 1 to 7, when the core is above 10 degrees in full darkness with the moon below the horizon for about 1.8 hours a night.
May, Jun and Jul
Best months for the core
13°
Highest point of the core, due south
70%
Average cloud amount over the year
13
Top core score out of 100, in June
The core clears 10 degrees during full darkness on most nights from April to August. In January, February, March, September, October, November and December it is 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 | 70% |
| February | 0 | Core not visible | 0 | 67% |
| March | 0 | March 25 to 31 | 0.0 | 67% |
| April | 4 | April 6 to 12 | 0.6 | 69% |
| May | 8 | May 4 to 10 | 1.1 | 73% |
| June | 13 | June 1 to 7 | 1.8 | 70% |
| July | 12 | July 1 to 7 | 1.4 | 65% |
| August | 6 | August 1 to 7 | 0.7 | 64% |
| September | 0 | September 1 to 7 | 0.1 | 65% |
| October | 0 | Core not visible | 0 | 73% |
| November | 0 | Core not visible | 0 | 78% |
| 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
- May: May 4 is the best night. The core is above 10 degrees and the moon is down from 3:15 am to 4:15 am, with the moon 2% lit that night.
- June: June 4 is the best night. The core is above 10 degrees and the moon is down from 1:15 am to 2:55 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 1:15 am to 2:35 am, with the moon 5% lit that night.
Clock times are Eastern time with daylight saving applied. The best nights fall around the new moon, so the dates shift by about 11 days each year.
About the park
Isle Royale National Park is a national park in Michigan. The National Park Service places its center at 48.01 degrees north and 88.83 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.
How Isle Royale National Park compares
Its best monthly core score of 13 ranks 52 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 Isle Royale National Park runs from 64% in August to 78% in November.
The score ranks months and parks. It is not a forecast for any night, and it leaves out local weather, smoke and light from nearby towns. How the core score works.
Nearest parks
Sources and method
- Sun, Moon and galactic centre positions calculated for the park's latitude and longitude from the low-precision formulas in Paul Schlyter's "Computing planetary positions", with the standard sidereal-time and horizon formulas. The code is checked against known events: new and full moons within 5 minutes, and the September equinox within 1 minute.
- Cloud: monthly mean cloud amount, 25-year Meteorological and Solar Monthly & Annual Climatologies (January 2001 - December 2025), from NASA POWER (version v2.10.1, source SYN1DEG), accessed October 19, 2026. Data obtained from NASA Langley Research Center POWER Project.
- Park facts: National Park Service.