Anyhow, the conversation evolved (or devolved, depending your frame of reference) into a discussion of antonyms and synonyms. We agreed: synonyms of dusk include "twilight" and (this was my contribution) "gloaming" (love that word!). Antonyms for dusk are "dawn" and . . .??
At this point, I was a bit stumped. Maybe it's because whereas I experience dusk frequently (every day, essentially), dawn is ... something I experience only under protest or in light of early flight schedules. So, I turned to the internet while everyone else returned to work. But hey, I charge by the hour, so I figured I could put in a couple free minutes to satisfy the itch for symmetry.
What I found:
Dusk vs Dawn
Twilight vs First light
Sundown vs Sunrise (or Sunup)
Nightfall vs Daybreak
Dawn or dusk? Who knows? But look at those lovely lenticular clouds!
Dusk vs Dawn
Twilight vs First light
Sundown vs Sunrise (or Sunup)
Nightfall vs Daybreak
Dawn or dusk? Who knows? But look at those lovely lenticular clouds!But then, I ran into trouble:
Gloaming vs ... what?? Gleaming? (I rather like that, but don't think it's the case.)
Eventide vs ... uh ...
Gloaming vs ... what?? Gleaming? (I rather like that, but don't think it's the case.)
Eventide vs ... uh ...
And what about crepuscular light? Does that only apply to evening/dusk? If so, then what do you call the "light before the dawn?"
At that point, I had to stop and get to work, because the itch to find the right words was beginning to feel more like a rash. But I've been turning those terms over in my mind all day... and now it's long past dusk.

