15.9 usable nights
13–17 in the middle half of years · 5.5 typically near a dark moon.
341 astronomical-dark hours in an average month
20-year trip-planning baseline
Best time to stargaze at Sierra Vista
May: 23.7 usable nights on average. Use this seasonal climate baseline to choose a month, then use the live forecast to choose a night.
Site darkness · modelled, not measured
Brightened skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.20.3–20.9 mag/arcsec²
The short answer
May has been strongest.
It averages 23.7 usable nights, versus 3.8 in July. A typical May lands between 22 and 25 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
14.8 usable nights
12–19 in the middle half of years · 4.5 typically near a dark moon.
284 astronomical-dark hours in an average month
17.8 usable nights
14–23 in the middle half of years · 5.7 typically near a dark moon.
292 astronomical-dark hours in an average month
20.4 usable nights
18–22 in the middle half of years · 6.8 typically near a dark moon.
240 astronomical-dark hours in an average month
23.7 usable nights
22–25 in the middle half of years · 7.7 typically near a dark moon.
224 astronomical-dark hours in an average month
19.3 usable nights
15–23 in the middle half of years · 6.4 typically near a dark moon.
180 astronomical-dark hours in an average month
3.8 usable nights
2–5 in the middle half of years · 1.1 typically near a dark moon.
203 astronomical-dark hours in an average month
6.7 usable nights
4–8 in the middle half of years · 1.8 typically near a dark moon.
248 astronomical-dark hours in an average month
17.6 usable nights
15–21 in the middle half of years · 6.1 typically near a dark moon.
262 astronomical-dark hours in an average month
22.6 usable nights
19–26 in the middle half of years · 7.3 typically near a dark moon.
310 astronomical-dark hours in an average month
18.9 usable nights
17–22 in the middle half of years · 6.4 typically near a dark moon.
324 astronomical-dark hours in an average month
15.1 usable nights
13–17 in the middle half of years · 5.7 typically near a dark moon.
342 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.