9.1 usable nights
6–12 in the middle half of years · 2.5 typically near a dark moon.
345 astronomical-dark hours in an average month
20-year trip-planning baseline
Best time to stargaze at Cupertino
July: 27.1 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.18.8–19.5 mag/arcsec²
The short answer
July has been strongest.
It averages 27.1 usable nights, versus 8.8 in December. A typical July lands between 25 and 30 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
10.0 usable nights
6–14 in the middle half of years · 3.1 typically near a dark moon.
289 astronomical-dark hours in an average month
10.7 usable nights
9–13 in the middle half of years · 2.8 typically near a dark moon.
281 astronomical-dark hours in an average month
13.8 usable nights
12–17 in the middle half of years · 4.3 typically near a dark moon.
239 astronomical-dark hours in an average month
19.4 usable nights
16–23 in the middle half of years · 6.7 typically near a dark moon.
188 astronomical-dark hours in an average month
23.4 usable nights
21–26 in the middle half of years · 8.0 typically near a dark moon.
180 astronomical-dark hours in an average month
27.1 usable nights
25–30 in the middle half of years · 8.9 typically near a dark moon.
186 astronomical-dark hours in an average month
26.9 usable nights
26–29 in the middle half of years · 8.8 typically near a dark moon.
228 astronomical-dark hours in an average month
24.9 usable nights
23–27 in the middle half of years · 8.7 typically near a dark moon.
252 astronomical-dark hours in an average month
20.5 usable nights
19–23 in the middle half of years · 6.8 typically near a dark moon.
309 astronomical-dark hours in an average month
14.1 usable nights
12–16 in the middle half of years · 4.3 typically near a dark moon.
328 astronomical-dark hours in an average month
8.8 usable nights
5–12 in the middle half of years · 3.1 typically near a dark moon.
363 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.