Okay I know this is like 4th grade science or something, but I think with my stroke I just can’t seem to picture why the sun is “on” or “off” for most of the day up at the North Pole or down at South Pole, and yet at the equator days are very regular year ’round.
I keep picturing the Earth on its axis, but I just can’t seem to figure out how the sun shines differently at different latitudes.
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The other explanations are good and it sounds like you got it but if you want to visualize or even demonstrate it to literal 5yo children do this:
Place a lamp in the middle of a room, remove any other light source. Get an apple or orange. Let them stab a pen through it. Put a little tack anywhere on it. Then make them slowly walk around the lamp in a circle with the apple. After one circle you say that is a year. Then let them keep walking in the circle and make them slowly spin the pen which spins the apple – tell them to watch the surface of the apple and also the tack which is actually “where they live” and tell them that’s day and night. Then last make them tilt the pen while they keep circling the lamp and spinning the apple and make sure to tell them they keep tilting it in the exact same direction all the time so the tilt is always the same (this is the most counterintuitive step, that the tilt doesn’t change at all as you move around. Like.. make it always face the same corner of the ceiling as they move around). If they struggle take over and show them how you mean that thing with the tilt, then hand the apple back. Then say that makes summer and winter because the days are longer or shorter and the sun is hitting more or less direct. And lo and behold at one of the the poles it’s either “always” day or “always” night for a while.
Or just show them a 3 minute youtube video but that’s fucking lame and they won’t remember.
You know how in the summer the days are longer and the nights are shorter?
How the sun will rise very early in the morning and set late in the evening in the summer and in the winter it will be the other way around with sun not rising until it is already very later in the morning and setting very early in the afternoon?
This phenomenon gets more and more extreme as you go further away from the equator.
At high latitudes the sun will only be up for a few hours in the winter and in the summer it will set very late at night and rise very early in the morning.
If you go beyond the arctic circle, it will get so extrem that at some point in the summer the sun will not really set at all. It will dip down towards the horizon and rise up again without ever having fully set.
In the winter it is the other way around the sun almost rises around but it never quite makes it above the the horizon and never gets beyond twilight.
If you go closer to the poles the time the sun stays up or down becomes longer and at the poles you have basically a long never ending day during the summer and a night that last all throughout winter.
The reason for this is that the earth’s axis is tilted.
The earth’s axis, around which the earth spins once per day, goes from pole to pole.
If that axis was at a right angle to the direction the sun is days would always be the same length and we would have no seasons.
However it isn’t quite the axis is slightly tilted.
Around the end of June the south pole points away from the sun and the north pole towards it. The south pole and the area around it doesn’t get any sunlight not matter how much the earth turns because it is on the dark side of the earth.
The axis keeps pointing into the same direction all year long. but as the earth moves to be on the other side of the sun, what was a tilt away from the sun becomes a tilt towards it.
During the end of December the north pole points away from the sun and the south pole towards it. The south pole gets sunlight and the north pole doesn’t
Throughout the year the axis goes from pointing away from the sun in the northern hemisphere to being completely perpendicular to the sun towards the end of march and pointing away from it near the end of June to being perpendicular again in the end of September and pointing away from it again shortly before x-mas.
When the axis points away from the sun the days are shortest and nights are longest, when it is at an right angle the day and night are exactly equally long and when it points towards the sun the nights are shortest and the days are longest.
Don’t think of it as turning on or off. Think of it as a path the sun takes across the sky. At the equator, the sun rises in the east, follows an arc across the sky and then sets in the west. Pretty simple, right?
Imagine lying flat on the ground in your living room with a light directly above you. If you roll across the ground and keep your head facing straight, you’ll see something similar. The light will come into your view, travel across your view, then disappear on the other side.
Now imagine standing up directly underneath the light, looking up towards it. Spin around and you’ll notice that the light does little loops but always stays in sight.
This is basically what the Earth is doing. At the equator and on the spring and fall equinoxes, it’s like laying flat on the floor. At the poles during the summer, it’s more like standing up. During winter at the poles, it’d be like doing a headstand. As the year progress, the Earth is basically just shifting between those positions. The closer you are to the poles, the more pronounced the effect is. At the equator, it’s virtually non-existent.
There’s two ways to look at this – from space and from the ground.
From space, the Earth’s axis is tilted relative to its orbit. So in Northern summer, the north pole is tilted towards the Sun. The north pole itself doesn’t move as the Earth rotates, and the land near it doesn’t move by enough to ever end up on the night side of the planet (that is, the side facing away from the Sun).
But the more interesting picture, I think, is from the ground.
You probably think of the Sun as rising in the east, rising up directly overhead, and setting in the west. But that picture turns out to only be true at the equator on the equinoxes. Everywhere else on Earth, the story’s a bit different.
Instead, the Sun follows a circular track in your sky each day. (Technically, it’s not quite a circle, but it’s close enough for our purposes here.) At the equator, that track is oriented straight up and down – that is, if you imagine filling in that circle to make a disc, the disc would be a vertical flat plane. As you move away from the equator, though, that disc tilts by an angle equal to your latitude. At a typical latitude of most people reading these words – around 30 or 35 degrees North – the circle is tilted by 30 or 35 degrees. At the equinox, the Sun still rises in the east, but it follows a *slanted* path, peaks about 30 or 35 degrees *below* the point directly overhead (the *zenith*), and comes back down along a slanted path to set in the West.
If the Earth had no tilt to its spin, that would be the whole story. But because it does, we also have seasons. The seasons cause the Sun’s track to shift in the sky towards the north or south celestial pole – that is, the point in the sky you’d find if you took the north pole or south pole of the Earth and projected it out into infinity.
During northern hemisphere summer, the circle the sun follows “contracts towards the north celestial pole”. Since this pole is above the horizon in the northern hemisphere, this causes the Sun to be up for more than half of the day (since its track is “pulled” towards a point above the horizon). The Sun therefore rises somewhat north of due east, rises up into the sky, peaks in the southern sky, then follows a slanted path down to set north of due west. It dips below the northwest horizon, passes under the northern horizon overnight, and rises again in the northeast horizon the next morning.
If you’re far enough north, though, the Sun’s track is VERY tilted. If you’re at, say, 80 degrees north, the Sun’s track is only tilted by 10 degrees. That means that at the equinox, the Sun was only ever 10 degrees above or below the horizon. But the maximum effect of the seasons (23.5 degrees, which is the tilt of the Earth’s axis) is larger than that. So the Sun ends up being pulled from 10 degrees below the northern horizon at the equinox to 13.5 degrees **above** the northern horizon at the summer solstice. The entire track sits above the horizon, and you get the midnight sun.
During northern hemisphere winter, the opposite happens. The sun’s track moves *away* from the northern celestial pole in the sky. At temperate latitudes, the Sun now rises *south* of due east, rises to peak in the southern sky, and sets *south* of due west. It passes under the western, northwestern, northern, northeastern, and eastern horizons before rising again in the northeast the next day, and is up for much less than half the day.
If you’re far enough north, this effect can pull the entire sun’s track *below* the horizon, resulting in a polar night.
In short, there are two main factors that contribute to the Sun’s highest and lowest point each day:
* Your latitude. The Sun’s “baseline” highest point is (90 minus your latitude) degrees above the horizon, and its “baseline” lowest point is (90 minus your latitude degrees) below it.
* The seasons. During your hemisphere’s summer, the highest and lowest points rise by as much as 23.5 degrees. At the equinox, it follows its baselines. And during your hemisphere’s winter, the highest and lowest points *fall* by as much as 23.5 degrees. This pattern roughly follows a sine wave over the course of a year.
(There are some other minor factors, too, but this is enough to explain most of the seasons.)
Like others have pointed out, it’s due to the earths tilted axis,I believe it’s easier to understand by visualizing it, so here’s a link that shows the earth and sun on the winter solstice (when Antarctica would have perpetual sunlight)
https://www.jpl.nasa.gov/edu/events/2020/12/21/winter-solstice-in-the-northern-hemisphere/
The Earth is tilted. During the polar summer, that pole is pointed “towards” the Sun, like this (assuming North pole):
Sun <Earth
See how the tilted arrow points towards the Sun at the top? Does it make sense how the Sun is going to consistently shine there? Even as the Earth spins during the day, the area at the top doesn’t “spin out” of pointing towards the Sun.
Ok, now, go to the other half of the year. The Earth is going to be on the other side of the sun, but it still ***faces*** the same way, like this:
Earth> Sun
Now the top of the tilted arrow points ***away*** from the Sun at the top. In the same way, even as the Earth spins during the day, the area at the top doesn’t “spin in” to pointing towards the Sun.
The earth tilts a bit throughout the year so that in the summer, the pole is tilted towards the sun and in the winter the pole is tilted away. The easiest way to think of this is to imagine what would happen if the earth tilted all the way so that it’s axis faced the sun and it was basically rolling around on its side. One pole would get constant sun basically as if it was always noon and the other would have constant midnight and the equator would have permanent twilight.
Obviously the earth doesn’t tilt nearly that much, but near the poles where you’re already kind of close to the “constant twilight” state all it takes is a small tilt to get constant daylight or night. The key is that the sun is always near the horizon (just above or just below) rather than straight overhead in those cases so it’s more like constant dawn/dusk.
The sides of the earth don’t point directly at the sun. It tilts. This is why we have seasons. At certain times of the year, the north pole tilts towards the sun and the south pole away. At other times, it’s the opposite.
This is also responsible for the poles being light or dark for such long periods of time. The earth tilts towards the sun at one pole so, as it spins, those regions see the sun no matter which way they are facing in the rotation.
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