What is astronomical dawn?
Astronomical dawn is the moment the Sun's centre rises to 18° below the horizon. Before it, the sky is as dark as it gets; after it, a faint glow begins to brighten the eastern sky, though most people won't notice for a while. It is the earliest of the three dawns, followed by nautical (−12°) and civil dawn (−6°).
| Phase | Sun below horizon | What you see |
|---|---|---|
| Civil twilight | 0° to 6° | Enough light to work outdoors; brightest planets appear |
| Nautical twilight | 6° to 12° | Horizon still visible at sea; bright stars visible |
| Astronomical twilight | 12° to 18° | Sky looks dark to most people; faint glow remains |
| Night | more than 18° | No sunlight scattered in the sky |