Next new moons: –
We sampled 16 compass directions at 25, 50 and 90 km from the centre — the same rings the Find darkest nearby button on the map uses. “Typical” is the median of the 16 points.
| Distance | Darkest direction | Bortle there | Typical Bortle |
|---|---|---|---|
| 25 km | south-southwest | 4–5 | 5–6 |
| 50 km | south-southeast | 1–4 | 4–5 |
| 90 km | south-southeast | 1–4 | 5–6 |
Yellow: Great Falls. Purple: the darkest sampled point at 25, 50 and 90 km.
The centre of Great Falls reads 255 on a 0–255 night-lights brightness scale (the sensor composite saturates at 255, so city cores cannot be told apart above this), which we estimate as Bortle 7–8. Among the 787 United States cities on this site it ranks 660 by brightness.
Sampling 16 directions at 25, 50 and 90 km, the nearest point at least two Bortle classes darker is about 25 km south-southwest of Great Falls. The table on this page lists the darkest direction at each distance; open the interactive map to scan around any other point.
It is an estimate from the light the ground sends upward (NASA VIIRS Black Marble, 2016 annual composite), combined with the light within 10 and 30 km and calibrated against 4,556 Globe at Night sky-quality-meter measurements. Checked against those measurements, the estimate is within one class of the measured value 78% of the time. The satellite image cannot separate class 1–3 skies from class 4, so the darkest band reads 1–4. Bare desert or snow can read 1–2 classes too bright. New suburbs or roads built after 2016 do not show yet. For an exact reading, measure on site with an SQM meter.
Around the new moon, on a clear night. A full moon brightens the sky as much as a small town does. The next new-moon dates are shown on this page.