0.3 usable nights
0–1 in the middle half of years · 0.1 typically near a dark moon.
362 astronomical-dark hours in an average month
20-year trip-planning baseline
When to plan an observing trip to Calgary
August: 6.0 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.17.7–18.4 mag/arcsec²
The short answer
August has been strongest.
It averages 6.0 usable nights, versus 0.0 in June. A typical August lands between 4 and 8 usable nights.
No astronomical darkness in June. Cloud cannot rescue a night when the sun never reaches 18° below the horizon.
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
1.1 usable nights
0–2 in the middle half of years · 0.1 typically near a dark moon.
292 astronomical-dark hours in an average month
1.6 usable nights
0–1 in the middle half of years · 0.4 typically near a dark moon.
260 astronomical-dark hours in an average month
3.0 usable nights
1–4 in the middle half of years · 1.1 typically near a dark moon.
172 astronomical-dark hours in an average month
2.0 usable nights
1–3 in the middle half of years · 0.6 typically near a dark moon.
68 astronomical-dark hours in an average month
0.0 usable nights
0–0 in the middle half of years · 0.0 typically near a dark moon.
0 astronomical-dark hours in an average month
0.6 usable nights
0–1 in the middle half of years · 0.1 typically near a dark moon.
25 astronomical-dark hours in an average month
6.0 usable nights
4–8 in the middle half of years · 2.4 typically near a dark moon.
151 astronomical-dark hours in an average month
5.5 usable nights
4–7 in the middle half of years · 1.5 typically near a dark moon.
224 astronomical-dark hours in an average month
2.8 usable nights
1–4 in the middle half of years · 1.1 typically near a dark moon.
299 astronomical-dark hours in an average month
0.8 usable nights
0–1 in the middle half of years · 0.5 typically near a dark moon.
339 astronomical-dark hours in an average month
0.5 usable nights
0–1 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.