Imagine you are at the pole in the late winter and have survived a deep dark loooong night. Finally the sun peeps over the horizon for a brief moment before going back down again.
WHere does it rise? What longitude does it first appear at? does it first appear at this longitude every year or does it vary from year to year? is it predictable where it will rise many years out?
First of all, the longitude will be very difficult to pin down, since it’ll mostly be moving along the horizon, not up or down.
But assuming you do pin it down, no, it won’t be at the same longitude every year. That would only happen if the year were an exact integer number of days. Since it’s about a quarter-day longer than an integer, the sunrise point will move almost 90 degrees each year.
And it won’t peep up briefly before going back down, either, at least not if you’re right at the pole. Right at the pole, there is only one sunrise and one sunset per year: It spirals up gradually for three months, then spirals back down gradually for three months, and then is dark for six (during which it’s still spiraling, just below the horizon where you can’t see it).
This all assumes that the horizon is perfectly uniform and level. If it’s not, then the first sunrise will probably always be at the lowest point on the horizon, or close to it (though the date of the sunrise will vary).
If you are exactly at the pole (north or south), then the sun’s apparent path is almost exactly parallel to the horizon, and it spirals around you once per day. If you are at the north pole, then from June-December, the sun slowly descends toward/below the horizon as it moves around you; from December-June, the sun slowly ascends as it spirals around you. It’s the other way around at the south pole.
As you approach the vernal equinox (March or September, depending on which pole you’re at), the half of the sky nearest to the sun gets brighter and brighter, and eventually the sun’s top edge peeks above the horizon - but it still continues spiraling around you, once per day. If you’re right AT the pole, the sun doesn’t peep over the horizon for a brief moment at the equinox; once it appears, it will then be above the horizon for the next six months or so.
Because the solar disc has a non-zero width, its top edge will appear above the horizon significantly before the equinox. Geometry-wise, the center of the solar disc would break the horizon right at the moment of equinox. So you’ll actually see some part of the sun for a good bit longer than six months.
Nevermind, ninja’d
thanks for fighting the ignorance. Of course, I should have realized it spiraled up and didn’t actually go down once it made its first appearance.
I take from this too, that its first appearance will ideally change approximately 90 degrees each year
I once calculated that it takes about 3 days to rise, that is from when the sun first appears to when it completely breaks away from the horizon. Twilight ought to last for weeks before rising. Setting is just the same thing in reverse.
In March, the sun’s latitude increases about 0.4 degrees every 24 hours. As the sun is about 0.5 degrees high, sunrise would take about 30 hours (or did I miss something). An observer would see the sun rotate 1 1/4 times around the horizon during a complete sunrise.
Hmm, I thought I understood this pretty well, but the more I think about it, the more puzzled I get. So right at the pole, the sun only rises and sets once. Below the Arctic Circle, the sun rises and sets 365 times. What about if I’m, say, 100 miles from the pole? Does it poke above the horizon briefly, then disappear, then the following “day” rise and stay risen for almost six months, then set and then briefly reappear?
Colophon: Between the pole and the circle, it will vary based on how far away you are. but basically, you nailed it.
Just a bit away from the pole, you’ll have just a few “normal” days and then 25 weeks of day or night. Just north of the circle, you’ll have lots of normal days, followed by a VERY long day or night.