The period when the sky darkens after sunset. It is civil until the Sun is 6° below the horizon (you can read outside), nautical until 12° (the horizon fades) and astronomical until 18°. Only then is the night truly dark for deep-sky objects.
ToolsWhat to see tonight?, The Moon tonight
Related terms
- Solstice
The moment the Sun reaches its greatest declination, +23.4° around 21 June and −23.4° around 21 December. In the northern hemisphere June brings the longest day and December the longest night. Around the June solstice in France and the UK, true darkness is short or missing.
- Dark adaptation
The time the eye takes to become sensitive in the dark: the pupil opens within seconds, but the retina gains most of its sensitivity over 20 to 30 minutes. A single bright white light undoes it all. That is why observers use a dim red light.
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