13.3 usable nights
11–16 in the middle half of years · 4.3 typically near a dark moon.
341 astronomical-dark hours in an average month
20-year trip-planning baseline
When to plan an observing trip to Chandler
October: 21.5 usable nights on average. A regional planning baseline, not a forecast for your trip.
Site darkness · modelled, not measured
Bright urban skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.18.0–18.8 mag/arcsec²
The short answer
October has been strongest.
It averages 21.5 usable nights, versus 5.5 in July. A typical October lands between 19 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
12.4 usable nights
10–15 in the middle half of years · 3.5 typically near a dark moon.
286 astronomical-dark hours in an average month
14.7 usable nights
13–18 in the middle half of years · 4.6 typically near a dark moon.
289 astronomical-dark hours in an average month
18.4 usable nights
17–21 in the middle half of years · 6.2 typically near a dark moon.
240 astronomical-dark hours in an average month
21.2 usable nights
20–24 in the middle half of years · 6.7 typically near a dark moon.
211 astronomical-dark hours in an average month
19.0 usable nights
15–24 in the middle half of years · 6.3 typically near a dark moon.
180 astronomical-dark hours in an average month
5.5 usable nights
2–7 in the middle half of years · 2.1 typically near a dark moon.
194 astronomical-dark hours in an average month
6.8 usable nights
3–10 in the middle half of years · 1.9 typically near a dark moon.
244 astronomical-dark hours in an average month
17.1 usable nights
14–21 in the middle half of years · 6.0 typically near a dark moon.
258 astronomical-dark hours in an average month
21.5 usable nights
19–25 in the middle half of years · 7.2 typically near a dark moon.
310 astronomical-dark hours in an average month
16.9 usable nights
16–19 in the middle half of years · 5.7 typically near a dark moon.
326 astronomical-dark hours in an average month
12.6 usable nights
10–16 in the middle half of years · 4.8 typically near a dark moon.
351 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.