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If you look at e.g. timeanddate, you can see not just sunrise and sunset times, but various twilights. What are they?
On the dusk side -- I expect more of my readers see dusk than dawn -- they are civil, nautical, and astronomical twilights.
Civil: the sun has set[1], but there's still refracted light so it's fairly bright and you won't get mugged.
Nautical: it is darker, and some stars are out, but you can still make out the horizon, making this the *perfect* time for old-fashioned navigation, where you need to see stars and the horizon.
Astronomical: the horizon is gone, and most people would just call this 'night'. But astronomers trying to observe the faintest objects will still complain about natural light pollution.
They're non-symmetric with respect to work: with civil, civilians can still do work, or be coming home from work; for nautical, this is the best/only time that navigators can work; for astronomical, astronomers still *can't* work.
In dusk order, they are CNA, and I don't a better mnemonic than "CNAs really like sunset." (Certified Nursing Assistants.) On the sunrise, side, astronomical obviously comes first, and the sky gets marginally too light for astronomers.
In a fantasy setting, one might imagine various vampire twilights, depending on how robust your vampires are. From "the sun has set, but there is still time to scurry home safely" to "the sun has not yet set but the vampires are already out."
[1] Technical details: sunset means the entire sun has set, i.e. that the upper edge of the sun has passed below the horizon. But the twilights are defined by how many degrees the *center* of the sun is below the horizon: 6, 12, or 18. The sun itself seems to be half a degree wide.
On the dusk side -- I expect more of my readers see dusk than dawn -- they are civil, nautical, and astronomical twilights.
Civil: the sun has set[1], but there's still refracted light so it's fairly bright and you won't get mugged.
Nautical: it is darker, and some stars are out, but you can still make out the horizon, making this the *perfect* time for old-fashioned navigation, where you need to see stars and the horizon.
Astronomical: the horizon is gone, and most people would just call this 'night'. But astronomers trying to observe the faintest objects will still complain about natural light pollution.
They're non-symmetric with respect to work: with civil, civilians can still do work, or be coming home from work; for nautical, this is the best/only time that navigators can work; for astronomical, astronomers still *can't* work.
In dusk order, they are CNA, and I don't a better mnemonic than "CNAs really like sunset." (Certified Nursing Assistants.) On the sunrise, side, astronomical obviously comes first, and the sky gets marginally too light for astronomers.
In a fantasy setting, one might imagine various vampire twilights, depending on how robust your vampires are. From "the sun has set, but there is still time to scurry home safely" to "the sun has not yet set but the vampires are already out."
[1] Technical details: sunset means the entire sun has set, i.e. that the upper edge of the sun has passed below the horizon. But the twilights are defined by how many degrees the *center* of the sun is below the horizon: 6, 12, or 18. The sun itself seems to be half a degree wide.