13.8 usable nights
13–16 in the middle half of years · 4.6 typically near a dark moon.
338 astronomical-dark hours in an average month
20-year trip-planning baseline
When to plan an observing trip to Big Bend National Park
October: 19.1 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.21.9–21.9 mag/arcsec²
The short answer
October has been strongest.
It averages 19.1 usable nights, versus 8.1 in August. A typical October lands between 17 and 22 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
12.3 usable nights
9–15 in the middle half of years · 3.6 typically near a dark moon.
283 astronomical-dark hours in an average month
14.1 usable nights
9–20 in the middle half of years · 4.8 typically near a dark moon.
296 astronomical-dark hours in an average month
14.8 usable nights
13–17 in the middle half of years · 4.8 typically near a dark moon.
241 astronomical-dark hours in an average month
15.5 usable nights
13–20 in the middle half of years · 5.0 typically near a dark moon.
245 astronomical-dark hours in an average month
12.4 usable nights
10–14 in the middle half of years · 3.5 typically near a dark moon.
182 astronomical-dark hours in an average month
8.2 usable nights
6–10 in the middle half of years · 3.3 typically near a dark moon.
227 astronomical-dark hours in an average month
8.1 usable nights
5–14 in the middle half of years · 2.6 typically near a dark moon.
248 astronomical-dark hours in an average month
12.1 usable nights
9–16 in the middle half of years · 4.5 typically near a dark moon.
267 astronomical-dark hours in an average month
19.1 usable nights
17–22 in the middle half of years · 6.8 typically near a dark moon.
310 astronomical-dark hours in an average month
17.9 usable nights
13–22 in the middle half of years · 5.6 typically near a dark moon.
321 astronomical-dark hours in an average month
13.3 usable nights
11–16 in the middle half of years · 4.6 typically near a dark moon.
327 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.