Yesterday we talked about twilight, and what that entails. Also, you found out – in case you didn’t know already – that astronomers like the dark. We don’t like artificial light. We want the night skies to be as dark and pristine as possible, so we can observe, photograph, and do research. And depending on the time of the year, the nights go by really fast, or awfully slow.
Darkness is directly related to a couple of factors: time of sunrise and sunset, and where you are on the planet. As you go father north (or south) from the equator, the sun sets at more of an angle, which means that it takes longer to travel through the zones of twilight. Twilight at the equator is quick, because the sun sets nearly perpendicular to the horizon. But the farther from the equator you go, the angle increases, so much so that once you get above the Arctic Circle the sun never sets for weeks at a time during the summer, and never rises for weeks during the winter. Here in Grand Rapids the sun sets at a 47° angle relative to the horizon, so we’re around the “middle ground” of twilight time.
We’re going to use the Summer Solstice and the Winter Solstice as examples.
From here in Grand Rapids, around June 21st each year we have the longest days. Morning and evening twilight last over two hours before and after the sun has disappeared over the horizon. For this reason, darkness is at a premium. Evening twilight ends at 11.44pm, and morning twilight begins at 3.45am the next morning. That equals just under four (4) hours of complete darkness. That’s not much time to do research, etc. But at least you’re comfortable, or kind of warm.
Around December 21st each year we have the shortest days. And even though twilight is taken basically the same time to fade out and in, if we have short days, we have to have long nights. On that date evening twilight ends at 6.54pm, and morning twilight begins at 6.27am. That’s almost twelve (12) hours of darkness! Think of what you could do with that much darkness! Of course, here in Michigan you have two problems: it’s winter so it’s probably cloudy, and because it’s winter, it’s definitely cold.
So there are always trade offs. Short warm nights or long cold ones. But no matter what the weather, if it’s clear when it’s dark, you will find the astronomers out under the stars, striving to understand the unknown.
(Note: to determine the sunrise/sunset times, plus twilight times, the program Moonrise was used. It is a great shareware program that determines sunrise/sunset, moonrise/moonset and other features for your area.)