Caoimhín's Content

Today, we are going to be taking a look at the sunset for autumn, but we’re mostly going to be looking at it from the North Pole. However we’ll start with sunset from Ireland in late September.

As the Sun sets, first it drops behind trees and buildings, then the horizon itself. We know the Sun goes under the horizon before the sky gets truly dark, there is always some amount of sunset glow extending after the Sun sets. If we rid of all of our trees and buildings and just take a look at a perfectly flat horizon, we can confirm that while the Sun is just under the horizon and the sky is still plenty bright. Really, there’s a little bit of an optical illusion going on with the sunset. The air around us bends the light of the Sun, especially close to the horizon when we’re looking through quite a lot of atmosphere. The light is bent so much that even though the Sun appears to be above the horizon, it is actually below it.

In Stellarium we can test this by taking away the atmosphere. With the Sun clearly above the horizon, and zoomed in we can see some sunspots as well, if we get rid of the atmosphere, the Sun “jumps” under the horizon, or nearly under the horizon. With the atmosphere out of the way, we can see a little bit of the corona, that kind of fluffiness of the Sun’s magnetic field stretching out from its surface. Moving a little ahead, so that the disk of the Sun itself is definitely under the horizon, if we bring back our atmosphere it hops back up above the horizon again. This effect means that even on the equinox, when the day should be 12 hours long, it appears a little bit longer. As well as bending it, the atmosphere also spreads out the light of the Sun. Even when the Sun appears to be under the horizon, even allowing for the distortion of the atmosphere, the sky remains pretty bright and it will stay quite bright for a while. Especially here in the Northern Hemisphere, high on the planet, it takes a while for the glow of the Sun to fade away. We can see still some orange glow quite a bit later, even though the rest of the sky is getting dark. This is partly down to the axial tilt, making us see the ecliptic at a steep angle. The Sun goes under the horizon at an angle following the line of the ecliptic. Even though it is under the horizon, it takes a while for it to drop further under the horizon due to that steep angle.

If we hop up to the North Pole, the effect is even more apparent. Using Stellarium, we need to click as high up on the map as we can and then change the numerical value of the latitude to get all the way up to exactly the North Pole at 90 degrees. Once we’re directly at the North Pole, on the date of the autumnal equinox, the Sun appears to be just above the horizon. We’re sticking with a perfectly flat horizon, and the Sun seems to be just above it. If we move through days there, we can see the height changing because the Sun is getting lower as we move closer and closer to wintertime. For most of us, the Sun is going to set earlier, but at the North Pole, it is about to set. When you’re at the North Pole, the Sun will stay above the horizon for the entire summer, and it will go under the horizon for the entire winter, with a span of a twilight glow in between. The sky in September is still bright, the Sun is still up for the entire day. We’re just at the equinox 22nd, and if we go a couple of days further forward the Sun drops under the horizon.

Continuing ahead, the Sun is definitely under the horizon by the 25th. We’re at the North Pole, so we don’t really have to worry about time zones or anything, although Stellarium is giving us this particular time of minus two hours from UTC, as it is in Greenland. Of course, no timezone matters too much when you’re at the North Pole. Staying focused on the Sun we’ll move through time Sun to see when the it is just completely under the horizon, which seems to be on the 24th, with the atmosphere distorting things. We’ll pull ourselves back up in time a bit until the Sun is above and just touching the horizon, on the 23rd. If we get rid of the atmosphere, it’s completely below the horizon, so the Sun sets for the North Pole a little bit earlier than the 23rd, if there’s no atmosphere. With the atmosphere on, we have to wait a little bit longer for the 25th before the Sun is completely under the horizon. Either way, that is the Sun going down, and because of the way it works at the North Pole, once the Sun is set, it’s not going to come back up for quite a while. It’s not going to start to get higher again until we pass midwinter, it’s just going to keep getting lower and lower as nighttime slowly sets in.

The best way to see this is with your view fixed on the Sun. This means counter-rotating to compensate for the fact that the Earth is rotating. This allows your view to remain fixed on the Sun. Pushing forward from sunset to darkness, and the Moon comes whizzing past, showing that we’re moving through time pretty quickly. Again the Sun is drifting under the horizon at an angle, I guess almost a spiral if we weren’t stabilizing for the Earth. As such, it gets quite dark by Mid-November or so, but there’s twilight for really almost the entire month of October. It clearly starts to get dark in early October, with bright objects like Venus and Jupiter appearing, but there’s still a little bit of an orange-yellow glow even as we get towards the end of that month. The Sun is currently setting for the North Pole. Given the date that this piece will be posted, the Sun will have just set, if we’re not allowing for the atmosphere, and it will set within a day if we are allowing for the atmosphere.

In real life, this would be locally complicated by the terrain. I’ve kept the horizon completely flat, and of course the North Pole, or the Arctic generally, is reasonably flat. It doesn’t have as many mountains because of course it’s not a continent. The Arctic, the North Polar Ice Cap is really just ice floating on top of the ocean. Removing any stabilization, not locking on the Sun, causes it to appear to go around, skirting along the horizon. As we move forward and as we speed it up, it does look a little bit strange. However, it can slowly be seen starting to darken as we come into October and that twilight will stay with us right into the middle of October and a little through to the end. I’m going to lock back onto something just so it’s not so odd looking, as the Sun flying around and around does look pretty strange. If we lock onto the Sun, then it’ll stay in the same apparent position as we move through time, and a featureless horizon makes it impossible to tell that there’s turning happening at all.

This phenomenon, the Sun setting for the North Pole, for the last and only time this year, is pretty unique, shared only by the South Pole. Taking a look at this was suggested by a commenter right here on this website. All of these posts of course have a video attached, and these posts are a corrected transcription of those videos. Pulling way back in the year, the Sun starts reaching its highest for the summer. When the Sun is at its highest, of course, if we move through time without the Sun-stabilized view, it still makes a full circle in the sky over the day, and it stays quite high in the sky the whole time. Of course, the highest the Sun gets in the Arctic is still low in the sky. It’s the highest it’s going to get at the North Pole, but of course that’s still significantly lower than everywhere else on Earth when the Sun is at its highest for those subjective locations. However, this is higher than the Sun gets, for example, for wintertime here in Ireland. Soon the Sun in the middle of winter will be quite low for us here in Ireland, of course not quite as low as it is currently getting for anyone who is at the North Pole.

As I mentioned, taking a look at this was suggested by a commenter who mentioned the fact that the Sun would be setting and questioned the effects that that would have. Of course the Sun setting for the North Pole is going to cause the temperature to go down. The North Pole is in nighttime for months and months, which causes the temperature to drop, and that mass of cold air in northern winter cools a lot of the surrounding area as well. If the axial tilt wasn’t so drastic, the effect would be quite different. The tilt of the Earth is the reason that we have the seasons the way that we have them, if we were less tilted, there would be far, far less seasonality. Looking at a map or a globe, it is noticeable in the Northern hemisphere, less so in the Southern hemisphere, there’s a fair bit of ice on the land. There is still at least a bit of ice on the land of the Northern Hemisphere. Those large land masses cool down and that causes huge, huge swings in temperature, more so than you’d have in places that are near water, with the moderating effect of the oceans. Of course, Antarctica itself being a huge landmass, it also sees huge drops in temperature. We’re going to come down a little bit to a location still very far in the north latitudes. We’ll go a little bit further north than Iceland, a little bit further north than Alaska, but still quite a few degrees from the North Pole. We’re going to Longyearbyen at about 76 degrees North. This puts us almost 15 degrees away from the North Pole.

That’s going to put the Sun back up in the sky. We’ll move back a little bit closer to the 25th. The Sun would have just about set for that date at the north pole. From our more southern location, we can see that the Sun reaches its highest during the day at midday, it drops under the horizon for nighttime and comes back up again as expected. For the northern latitudes that are still not quite at the North Pole, but are still in the Northern Circle or the Arctic Circle, they’re still going to be experiencing a night and a day, at least for another little while. As we move closer and closer into winter, we will come to a point where the Sun stops rising for these locations. The Sun is truly setting, really producing nighttime rather than an extended twilight. However, instead of rising, it merely comes close to rising, producing a glow without crossing the horizon. The Sun will have stopped coming up by the time we get into November.

There are big differences in the sunset at the North Pole and not as northerly latitudes a little south of the North Pole, but still in the Arctic Circle. Thanks to the tilt of the Earth, as well as the obvious effect of the seasons, it has the possibly more dramatic or at least equally dramatic effect of causing these very strange lengths of the day and night. In many locations it makes the day incredibly short or incredibly long. In the case of the actual North Pole itself, it’s really just one long day and one long night. Coming back to Ireland, we’re back at a location where the Sun is at least going to come above the horizon for every part of the year, even if it doesn’t come particularly far above the horizon in the middle of winter, but we’ll get back to that once we’re into the middle of winter.

I hope that you enjoyed this piece, if you did, please do like it. If there’s anything you’d like to see in the sky, then make sure you comment it here on my website, my YouTube channel or my Instagram. You can also subscribe to this website and to my accounts on those other platforms to see more. Thank you very much for reading and hopefully I’ll see you back here next time.