system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the difference between civil twilight, astronomical twilight, and nautical twilight?
gpt
Sunset

**Civil twilight** - sun is setting, artificial light is not needed

Sun falls below horizon

**Nautical twilight** - sun has set, but it is possible to navigate by the shape of the horizon

Horizon is no longer visible

**Astronomical twilight** - Bright stars and planets become visible

Sky is fully dark, all stars can be observed

And then in reverse in the morning.