2.4 usable nights
1–4 in the middle half of years · 0.8 typically near a dark moon.
352 astronomical-dark hours in an average month
20-year trip-planning baseline
When to plan an observing trip to Cherry Springs State Park
September: 8.0 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.21.6–21.8 mag/arcsec²
The short answer
September has been strongest.
It averages 8.0 usable nights, versus 1.0 in December. A typical September lands between 7 and 9 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
3.0 usable nights
2–5 in the middle half of years · 0.8 typically near a dark moon.
291 astronomical-dark hours in an average month
3.7 usable nights
2–5 in the middle half of years · 1.2 typically near a dark moon.
274 astronomical-dark hours in an average month
4.2 usable nights
2–6 in the middle half of years · 1.0 typically near a dark moon.
220 astronomical-dark hours in an average month
5.5 usable nights
4–7 in the middle half of years · 1.9 typically near a dark moon.
178 astronomical-dark hours in an average month
5.8 usable nights
5–7 in the middle half of years · 1.9 typically near a dark moon.
120 astronomical-dark hours in an average month
7.4 usable nights
5–9 in the middle half of years · 1.6 typically near a dark moon.
156 astronomical-dark hours in an average month
6.4 usable nights
5–7 in the middle half of years · 1.7 typically near a dark moon.
206 astronomical-dark hours in an average month
8.0 usable nights
7–9 in the middle half of years · 3.1 typically near a dark moon.
248 astronomical-dark hours in an average month
5.2 usable nights
4–7 in the middle half of years · 1.6 typically near a dark moon.
305 astronomical-dark hours in an average month
4.0 usable nights
2–6 in the middle half of years · 1.5 typically near a dark moon.
330 astronomical-dark hours in an average month
1.0 usable nights
0–1 in the middle half of years · 0.3 typically near a dark moon.
371 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.