1.8 usable nights
1–2 in the middle half of years · 0.6 typically near a dark moon.
355 astronomical-dark hours in an average month
20-year trip-planning baseline
When to plan an observing trip to Acadia National Park
September: 8.4 usable nights on average. A regional planning baseline, not a forecast for your trip.
Site darkness · modelled, not measured
Threatened dark skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.21.6–21.7 mag/arcsec²
The short answer
September has been strongest.
It averages 8.4 usable nights, versus 1.8 in January. A typical September lands between 7 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
2.0 usable nights
1–3 in the middle half of years · 0.5 typically near a dark moon.
292 astronomical-dark hours in an average month
5.3 usable nights
4–7 in the middle half of years · 1.4 typically near a dark moon.
270 astronomical-dark hours in an average month
4.8 usable nights
3–7 in the middle half of years · 1.4 typically near a dark moon.
209 astronomical-dark hours in an average month
3.5 usable nights
2–4 in the middle half of years · 1.4 typically near a dark moon.
154 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.
120 astronomical-dark hours in an average month
3.4 usable nights
2–5 in the middle half of years · 0.8 typically near a dark moon.
132 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.
195 astronomical-dark hours in an average month
8.4 usable nights
7–10 in the middle half of years · 2.9 typically near a dark moon.
246 astronomical-dark hours in an average month
5.3 usable nights
4–7 in the middle half of years · 1.6 typically near a dark moon.
303 astronomical-dark hours in an average month
3.8 usable nights
3–5 in the middle half of years · 1.3 typically near a dark moon.
332 astronomical-dark hours in an average month
1.8 usable nights
0–3 in the middle half of years · 0.7 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.