12.6 usable nights
11–14 in the middle half of years · 4.7 typically near a dark moon.
207 astronomical-dark hours in an average month
20-year trip-planning baseline
When to plan an observing trip to Siding Spring Observatory
September: 17.6 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
September has been strongest.
It averages 17.6 usable nights, versus 10.8 in November. A typical September lands between 17 and 20 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
13.3 usable nights
12–16 in the middle half of years · 4.2 typically near a dark moon.
223 astronomical-dark hours in an average month
13.9 usable nights
11–17 in the middle half of years · 4.4 typically near a dark moon.
284 astronomical-dark hours in an average month
17.4 usable nights
15–20 in the middle half of years · 5.8 typically near a dark moon.
300 astronomical-dark hours in an average month
16.4 usable nights
14–18 in the middle half of years · 4.8 typically near a dark moon.
310 astronomical-dark hours in an average month
13.4 usable nights
10–16 in the middle half of years · 3.6 typically near a dark moon.
317 astronomical-dark hours in an average month
14.6 usable nights
11–17 in the middle half of years · 5.2 typically near a dark moon.
332 astronomical-dark hours in an average month
17.4 usable nights
15–20 in the middle half of years · 5.9 typically near a dark moon.
310 astronomical-dark hours in an average month
17.6 usable nights
17–20 in the middle half of years · 6.3 typically near a dark moon.
292 astronomical-dark hours in an average month
14.9 usable nights
13–18 in the middle half of years · 4.8 typically near a dark moon.
257 astronomical-dark hours in an average month
10.8 usable nights
8–14 in the middle half of years · 3.9 typically near a dark moon.
217 astronomical-dark hours in an average month
13.2 usable nights
11–15 in the middle half of years · 4.0 typically near a dark moon.
190 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.