When the moon is out of the way
5 windows in the next four months. The next runs from Thu, Sep 17 to Sun, Sep 20.
The next windows
| Window | Nights | Darkest |
|---|---|---|
| Thu, Sep 17 to Sun, Sep 20 | 4 | Darkest around Thu, Sep 17, when the moon is 45% lit |
| Sat, Oct 3 to Mon, Oct 19 | 17 | Darkest around Wed, Oct 7, when the moon is 0% lit |
| Sun, Nov 1 to Tue, Nov 17 | 17 | Darkest around Thu, Nov 5, when the moon is 0% lit |
| Mon, Nov 30 to Wed, Dec 16 | 17 | Darkest around Fri, Dec 4, when the moon is 0% lit |
| Tue, Dec 29 to Thu, Jan 14 | 17 | Darkest around Sun, Jan 3, when the moon is 0% lit |
Why these are longer than you expect
The usual advice is to go on the new moon, which gives three or four nights a month. That advice treats the moon as a phase, and phase on its own says very little. A moon that is 60% lit but sets at 10pm costs nothing after 10pm. A 35% moon that stays up until dawn costs the whole night.
These windows are grouped by how much of the astronomically dark hours the moon is actually above the horizon, weighted by how bright it is and how high it sits. That is the same calculation behind every score in the 14-night forecast, so the two never disagree about a night.
Cloud is the other half and it cannot be known this far ahead. Weather forecasts reach about 16 days. These windows are astronomy, which is why they run to four months: pick the window now, check the cloud nearer the time.