4.3 usable nights
3–6 in the middle half of years · 1.6 typically near a dark moon.
357 astronomical-dark hours in an average month
20-year trip-planning baseline
When to plan an observing trip to Katahdin Woods and Waters
September: 8.2 usable nights on average. A regional planning baseline, not a forecast for your trip.
Site darkness · modelled, not measured
Natural-dark skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.21.8–21.9 mag/arcsec²
The short answer
September has been strongest.
It averages 8.2 usable nights, versus 1.4 in June. A typical September lands between 8 and 10 usable nights.
Record2005–2024 · 20 complete years
Usable nightAt least 3 astronomical-dark hours and NASA POWER nighttime cloud ≤30%
Dark-moon nightUsable night with ≤25% illumination at local solar midnight
ResolutionCERES SYN1deg 1° cloud grid; regional climate, not a campsite guarantee
Seasonal fingerprint
Usable nights by month
Month by month
3.8 usable nights
2–6 in the middle half of years · 1.0 typically near a dark moon.
292 astronomical-dark hours in an average month
5.7 usable nights
5–7 in the middle half of years · 1.9 typically near a dark moon.
268 astronomical-dark hours in an average month
4.8 usable nights
3–6 in the middle half of years · 1.6 typically near a dark moon.
203 astronomical-dark hours in an average month
4.3 usable nights
3–5 in the middle half of years · 1.8 typically near a dark moon.
142 astronomical-dark hours in an average month
1.4 usable nights
0–2 in the middle half of years · 0.7 typically near a dark moon.
87 astronomical-dark hours in an average month
5.0 usable nights
3–6 in the middle half of years · 1.6 typically near a dark moon.
121 astronomical-dark hours in an average month
6.5 usable nights
5–8 in the middle half of years · 2.0 typically near a dark moon.
184 astronomical-dark hours in an average month
8.2 usable nights
8–10 in the middle half of years · 2.6 typically near a dark moon.
244 astronomical-dark hours in an average month
4.7 usable nights
3–6 in the middle half of years · 1.8 typically near a dark moon.
302 astronomical-dark hours in an average month
2.3 usable nights
1–3 in the middle half of years · 0.9 typically near a dark moon.
334 astronomical-dark hours in an average month
2.5 usable nights
1–3 in the middle half of years · 0.8 typically near a dark moon.
372 astronomical-dark hours in an average month
Use the baseline honestly
Climate chooses the month. Forecasts choose the night.
The cloud product is a roughly 1° regional grid. It can reveal seasonality, but it cannot know a mountain ridge, valley fog pocket, locked gate, smoke event or the exact sky you will get.
Source: NASA POWER daily data, parameter CLOUD_AMT_NIGHT from the CERES SYN1deg cloud product. GoodSeeing calculates astronomical darkness and lunar illumination independently for each place.