What exactly is Twilight?

No, it’s not the romantic vampire book. It’s the magical time before sunrise and after sunset that night photographers like me live for. At sunset, it’s the short span of time after the magical golden hour where light quickly changes and enchantment begins to occur in your camera. It’s the time night photographers get energized in preparation for a night’s capture of the elusive brilliance of starlight. Light changes very quickly and for me, that’s when my camera takes over where my eyes leave off. It can see much, much more than my eyes possibly can.

From earthsky.org, this article explains the three different types of twilight.