Okay, I thought this would be a great post because there’s a TON of ambiguity about dusk, dawn, sunset, sunrise….How long is a “sunset”? When exactly is dusk? Can there be a set time for dawn and dusk or is always “when things get darker or brighter outside”? And what about twilight, how does that fit into all of this?
Crepusclar celestial events refer to everything when the sun is “close” to the horizon. This is the time when you get the most beautiful colors in the sky as the sun’s rays become filtered in through the atmosphere. So why not learn about those actual phases so you can know more precisely what’s going on when you see that magical palette of rich oranges and reds off your favorite beach at sunset?!
First off, sunrises and sunsets.
This one is simple. Sunset is the exact moment trailing edge, which would be the “upper edge” of the sun sphere disappears below the horizon. The moment you can no longer see the “orb of the sun” is the last second of a sunset and “sunset phase” is over. Therefore, a sunset lasts exactly how long it takes for the trailing edge of the sun to disappear from the horizon after the leading edge of the sun first hits the horizon. Sunrise, the exact opposite, is the exact moment the trailing edge of the sun full emerges from the horizon. A sunrise “commences” when the leading edge first appears on the horizon, but the sphere is not yet visible, and a sunset “commences” when the leading edge first touches the horizon, but the full sphere is totally visible. Technically sunrise and sunset is when the geometric zenith distance of center of the Sun is 90.8333 degrees, but that’s “hyper technical”.
