5.7 usable nights
4–8 in the middle half of years · 1.9 typically near a dark moon.
161 astronomical-dark hours in an average month
20-year trip-planning baseline
When to plan an observing trip to Nelson
June: 10.2 usable nights on average. A regional planning baseline, not a forecast for your trip.
Site darkness · modelled, not measured
Brightened skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.20.7–21.2 mag/arcsec²
The short answer
June has been strongest.
It averages 10.2 usable nights, versus 4.7 in December. A typical June lands between 7 and 13 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
6.9 usable nights
5–9 in the middle half of years · 2.4 typically near a dark moon.
193 astronomical-dark hours in an average month
7.2 usable nights
6–8 in the middle half of years · 2.7 typically near a dark moon.
262 astronomical-dark hours in an average month
8.0 usable nights
6–9 in the middle half of years · 2.5 typically near a dark moon.
300 astronomical-dark hours in an average month
8.4 usable nights
6–11 in the middle half of years · 3.3 typically near a dark moon.
340 astronomical-dark hours in an average month
10.2 usable nights
7–13 in the middle half of years · 3.4 typically near a dark moon.
360 astronomical-dark hours in an average month
8.4 usable nights
6–10 in the middle half of years · 3.9 typically near a dark moon.
358 astronomical-dark hours in an average month
6.5 usable nights
4–8 in the middle half of years · 2.1 typically near a dark moon.
315 astronomical-dark hours in an average month
6.3 usable nights
5–7 in the middle half of years · 2.3 typically near a dark moon.
278 astronomical-dark hours in an average month
5.7 usable nights
3–7 in the middle half of years · 1.7 typically near a dark moon.
234 astronomical-dark hours in an average month
6.0 usable nights
5–7 in the middle half of years · 1.7 typically near a dark moon.
174 astronomical-dark hours in an average month
4.7 usable nights
3–6 in the middle half of years · 1.6 typically near a dark moon.
131 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.