0.3 usable nights
0–0 in the middle half of years · 0.1 typically near a dark moon.
358 astronomical-dark hours in an average month
20-year trip-planning baseline
When to plan an observing trip to Sault Ste. Marie
September: 3.5 usable nights on average. A regional planning baseline, not a forecast for your trip.
Site darkness · modelled, not measured
Bright skyBortle classes describe observed sky conditions; this brightness model does not establish a measured Bortle class.19.5–20.2 mag/arcsec²
The short answer
September has been strongest.
It averages 3.5 usable nights, versus 0.1 in June. A typical September lands between 1 and 5 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
0.8 usable nights
0–1 in the middle half of years · 0.3 typically near a dark moon.
292 astronomical-dark hours in an average month
2.5 usable nights
1–3 in the middle half of years · 0.5 typically near a dark moon.
267 astronomical-dark hours in an average month
1.5 usable nights
0–3 in the middle half of years · 0.3 typically near a dark moon.
200 astronomical-dark hours in an average month
0.9 usable nights
0–0 in the middle half of years · 0.3 typically near a dark moon.
138 astronomical-dark hours in an average month
0.1 usable nights
0–0 in the middle half of years · 0.1 typically near a dark moon.
68 astronomical-dark hours in an average month
1.0 usable nights
0–1 in the middle half of years · 0.2 typically near a dark moon.
111 astronomical-dark hours in an average month
1.9 usable nights
0–3 in the middle half of years · 0.3 typically near a dark moon.
179 astronomical-dark hours in an average month
3.5 usable nights
1–5 in the middle half of years · 0.9 typically near a dark moon.
244 astronomical-dark hours in an average month
1.9 usable nights
1–2 in the middle half of years · 0.7 typically near a dark moon.
302 astronomical-dark hours in an average month
1.2 usable nights
0–2 in the middle half of years · 0.6 typically near a dark moon.
335 astronomical-dark hours in an average month
0.5 usable nights
0–0 in the middle half of years · 0.1 typically near a dark moon.
372 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.