Vespertine

Determined to not be late for an outdoor, dusk screening of E.T. at the Edgefield Lodge, I checked online to see what time sunset was. And as it so often happens on the web, one things leads to another, and before I knew it, I was having one of those I did not know that moments.

I had always thought dusk was more or less synonymous with sunset, just as dawn meant sunrise, but apparently not.

Dawn is when light first appears in the morning sky. Sunrise is when the sun breaks the horizon, and sunset, well... duh. Dusk is when the last light leaves the sky. This diagram explains it all:

The best part of my "discovery" was the word vespertine, a biology term that describes something of or related to the evening.