Observing basics
曙暮光
Twilight
The interval after sunset when the sky still glows.
Civil −6°, nautical −12°, astronomical −18°: we use −18° for the dark window.
Related terms
- Elongation — Angular distance from the Sun for an inner planet.
- Meteor shower — Many meteors when Earth crosses a comet's dust trail.
- ZHR — The theoretical hourly rate of a shower under perfect skies.
- Sidereal day — One rotation relative to the stars, about 4 minutes short of a solar day.