9.6 usable nights
7–12 in the middle half of years · 3.0 typically near a dark moon.
310 astronomical-dark hours in an average month
20-year trip-planning baseline
When to plan an observing trip to Hilo
January: 9.6 usable nights on average. A regional planning baseline, not a forecast for your trip.
Site darkness · modelled, not measured
Threatened dark skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.21.5–21.7 mag/arcsec²
The short answer
January has been strongest.
It averages 9.6 usable nights, versus 3.4 in April. A typical January lands between 7 and 12 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
5.9 usable nights
5–8 in the middle half of years · 1.7 typically near a dark moon.
283 astronomical-dark hours in an average month
4.5 usable nights
2–7 in the middle half of years · 1.6 typically near a dark moon.
310 astronomical-dark hours in an average month
3.4 usable nights
2–4 in the middle half of years · 1.3 typically near a dark moon.
256 astronomical-dark hours in an average month
4.8 usable nights
3–7 in the middle half of years · 1.1 typically near a dark moon.
248 astronomical-dark hours in an average month
3.7 usable nights
2–5 in the middle half of years · 0.7 typically near a dark moon.
240 astronomical-dark hours in an average month
3.6 usable nights
3–4 in the middle half of years · 1.3 typically near a dark moon.
248 astronomical-dark hours in an average month
4.0 usable nights
2–5 in the middle half of years · 1.0 typically near a dark moon.
249 astronomical-dark hours in an average month
5.2 usable nights
3–7 in the middle half of years · 1.6 typically near a dark moon.
299 astronomical-dark hours in an average month
4.8 usable nights
3–7 in the middle half of years · 1.6 typically near a dark moon.
310 astronomical-dark hours in an average month
4.0 usable nights
2–6 in the middle half of years · 1.0 typically near a dark moon.
300 astronomical-dark hours in an average month
6.0 usable nights
3–8 in the middle half of years · 1.6 typically near a dark moon.
310 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.