I just noticed the sunset border on Flightradar24 maps. I wonder: what are the 4 shades of grey, and why are they relevant? Why not just show one?
$\begingroup$ I'd like to point out that a question called "3 stages of twilight" is inherently different from "four shades of grey on the FR24 map". First, because I need to know there are stages of twilight and, second, because I need to know that FlightRadar shows the stages of twilight. Then I can find that question and get the information I need. So, instead of calling this question a duplicate, it might have been more relevant to answer "these are the twilight stages" and point to the other question. As WPNSGuy did. $\endgroup$– texnicNov 12, 2022 at 19:37
Varying levels of daylight, going into night.
This previous question goes into much more detail, and it may indeed be related to the aeronautical definitions as day turns into night.
$\begingroup$ Upvote for being correct, but there might be a deeper meaning... For example, there is sunset, nautical twilight, etc. that have distinct meanings. Could it be related to these definitions? I don't have time or motivation to research, just throwing it out there... ;) $\endgroup$ Oct 22, 2022 at 16:52
1$\begingroup$ @Michael Hall - Looking through the FR24 glossary and FAQ, and searching for "day", "night", "grey", "gray", I see nothing related to the varying shades of grey. Of course, I may be just missing it. $\endgroup$– WPNSGuyOct 22, 2022 at 17:06