7.3 usable nights
4–9 in the middle half of years · 2.2 typically near a dark moon.
346 astronomical-dark hours in an average month
20-year trip-planning baseline
Best time to stargaze at Modesto
August: 26.4 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
Bright skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.18.9–19.6 mag/arcsec²
The short answer
August has been strongest.
It averages 26.4 usable nights, versus 7.2 in December. A typical August lands between 25 and 29 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
9.2 usable nights
7–12 in the middle half of years · 3.0 typically near a dark moon.
289 astronomical-dark hours in an average month
9.8 usable nights
8–13 in the middle half of years · 2.5 typically near a dark moon.
281 astronomical-dark hours in an average month
14.4 usable nights
12–17 in the middle half of years · 4.8 typically near a dark moon.
239 astronomical-dark hours in an average month
19.9 usable nights
17–21 in the middle half of years · 7.0 typically near a dark moon.
187 astronomical-dark hours in an average month
23.6 usable nights
21–26 in the middle half of years · 8.3 typically near a dark moon.
180 astronomical-dark hours in an average month
25.5 usable nights
23–29 in the middle half of years · 8.2 typically near a dark moon.
186 astronomical-dark hours in an average month
26.4 usable nights
25–29 in the middle half of years · 8.6 typically near a dark moon.
226 astronomical-dark hours in an average month
23.9 usable nights
21–26 in the middle half of years · 8.5 typically near a dark moon.
251 astronomical-dark hours in an average month
18.6 usable nights
16–21 in the middle half of years · 5.8 typically near a dark moon.
309 astronomical-dark hours in an average month
11.8 usable nights
9–14 in the middle half of years · 3.9 typically near a dark moon.
329 astronomical-dark hours in an average month
7.2 usable nights
4–9 in the middle half of years · 2.8 typically near a dark moon.
364 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.