About sunrise and sunset: that's a more interesting subject that it sounds like at first. The sunrise and sunset times have a few purposes, mostly unrelated to telling you about the sun. First, they make it clear at a glance that you're looking at a visual representation of a single day's events. It's surprisingly non-obvious how to make a user interface's purpose obvious! Second, they give context to the timing of events by subtly matching them up with the day-night cycle; despite the advent of artificial lighting, our species is still instinctively diurnal, and this is a great source of intuitions about time. Third, they look really nice without being visually confusing or clashing with the color palette.

Oh, and they also tell you when the sun rises and sets. I guess that's cool, too.