2.3 usable nights
1–4 in the middle half of years · 0.3 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 Bozeman
July: 13.0 usable nights on average. A regional planning baseline, not a forecast for your trip.
Site darkness · modelled, not measured
Brightened skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.20.0–20.6 mag/arcsec²
The short answer
July has been strongest.
It averages 13.0 usable nights, versus 2.0 in December. A typical July lands between 12 and 15 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
2.3 usable nights
1–4 in the middle half of years · 0.7 typically near a dark moon.
292 astronomical-dark hours in an average month
2.6 usable nights
1–4 in the middle half of years · 0.9 typically near a dark moon.
268 astronomical-dark hours in an average month
2.9 usable nights
1–4 in the middle half of years · 1.1 typically near a dark moon.
203 astronomical-dark hours in an average month
3.8 usable nights
1–5 in the middle half of years · 1.4 typically near a dark moon.
144 astronomical-dark hours in an average month
6.9 usable nights
4–10 in the middle half of years · 2.5 typically near a dark moon.
103 astronomical-dark hours in an average month
13.0 usable nights
12–15 in the middle half of years · 4.3 typically near a dark moon.
125 astronomical-dark hours in an average month
11.7 usable nights
10–12 in the middle half of years · 4.3 typically near a dark moon.
186 astronomical-dark hours in an average month
10.8 usable nights
9–13 in the middle half of years · 4.0 typically near a dark moon.
245 astronomical-dark hours in an average month
5.5 usable nights
3–8 in the middle half of years · 1.8 typically near a dark moon.
303 astronomical-dark hours in an average month
2.6 usable nights
1–3 in the middle half of years · 0.8 typically near a dark moon.
334 astronomical-dark hours in an average month
2.0 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.