Astronomical darkness is the moment the sky stops scattering the last of the Sun's light. It is the start of the best observing, not the end of the planning.
The first hour after darkness
Your eyes are still adapting. Pupils widen over several minutes, and the chemical change that gives you full night vision takes roughly 20 to 30 minutes. Use that time to set up, find your chair, and check the chart with a dim red light. Avoid white phone screens; even a few seconds can reset much of your adaptation.
Why the middle of the night wins
The sky rotates. Objects rise in the east and climb toward the south, where you look through less atmosphere. By local midnight, the summer Milky Way is high and the winter constellations are well placed. If your dark window is short, aim for the hour centered on local midnight rather than the first minute after twilight.
Watch the forecast strip
Cloud cover is hourly. A dark window with a clear start and a cloudy end is still usable if you go early. The best-window suggestion looks for the clearest consecutive stretch and ignores nights where the peak cloud cover is overwhelming.
Cold is a planning problem
The clearest nights are often the coldest. Bring more layers than you think you need, keep your phone warm, and stand on a mat rather than bare ground. A thermos does more for a session than an extra eyepiece.
Know when to stop
If the seeing is poor or clouds are thickening, pack up without regret. A short, comfortable session builds the habit; a miserable three-hour fight with clouds does not. The next clear night is usually only a few days away.
Sources and review
Updated October 21, 2026. Date-sensitive details can change.