And why leap year happens once per 4 years only to address this?
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Imagine you have a toy car that goes around a big circle track. The track has a sun in the center. Your toy car represents Earth. As it goes around the sun (which takes one year), it also spins around like a top (which is one day).
Now, the spinning (one day) isn’t exactly 24 hours like we see on our clocks. It’s a tiny bit less – 23 hours and 56 minutes. So, you might think after a while, our days and nights would get all mixed up, right?
Here’s the trick: while our toy car (Earth) is spinning, it’s also moving a little bit around the track (around the sun). Because of this little movement, by the time it completes its spin, it needs an extra 4 minutes to face the sun in the same way again, which makes our days 24 hours.
Now, about leap years! Our toy car (Earth) doesn’t take exactly 365 days to go around the sun track; it takes a little bit more than that. So, every 4 years, we add an extra day (February 29th) to make up for that extra time. This way, our calendars and seasons don’t get out of sync!
So, thanks to Earth’s journey around the sun and its spinning, our days stay right where they should be, and everything works out!
Because you also travel once around the sun, so the sun is on the other side of the earth, and day is still day.
The rotation of the earth, measured as 23 hours 56 ,minutes, is compared with the universe in general, measure against a distant star.
The leap year addresses a different thing – that the solar year – measured against the sun – is a bit less than 365¼ days. So we need to add another day every 4 years to keep the calendar from drifting compared to the seasons. We also skip a leap day 3 times in every 400 years – every cententenary year that isn’t divisible by 400 – to keep things even closer.
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A day is defined as the time between the Sun being in the same position in the sky, and an hour is 1/24th of that. So the clocks stay in sync with the day-night cycle because they’re based on it.
The Earth’s spin on its axis is *not* synced to the day-night cycle. That’s how a single rotation can be less than a complete day long; one complete spin of the Earth doesn’t put the Sun in exactly the same place.
I never thought about it, but if the Earth didn’t rotate, then 6 months after it was high noon, it would be midnight as we revolve around the sun (i.e. for a distinct location on the planet, if the sun was directly overhead, then 6 months later the sun would be on the exact opposite side of the planet). But, since the Earth rotates, as your calculations show, that would-be-midnight is flipped right back to being high noon, it just happened slowly over the course of six months. Neat!
You answered your own question with your calculation. In 6 months the earth is on the other side of the Sun, so you need 180 degree difference for daytime to keep facing the sun at the same time.
The 56 minutes is for a full 360 degree spin on axis, but one day is not 360 degrees of spinning, it’s a little bit more given that the earth not only rotates it also translates within its orbit.
Because the earth circles around the sun once a year. That removes one sun rise every year. Every year the earth rotates 366 times relative to the universe, but we only see 365 sun rises.
In other words, because the earth circles the sun, the sun rise actually happens roughly 4 minutes past each complete rotation every day.
so it does, sort of. The reason you don’t notice it is because of confusion between the length of a sidereal day which is 23hrs and 56 min and a solar day which is almost exactly 24 hours. A Sidreal day is the time it takes for the earth to do one 360 degree rotation, and if you started marking the time that the earth rotated 360 degrees at midnight on day one half a year later you would be marking time and midday and half a year after that you’d be marking time back at midnight.
However we mark our time on the solar day, which is the time it takes the same spot on the earth to face the center of the sun rotate and then face it again, the time between two noons. because the earth is orbiting the sun whilst rotating after 360deg of rotation the point on the earth that was facing the sun is now slightly offset, it turns out that to face the center of the sun again the earth needs to rotate just under 361 degrees.
so your confusion and many others is based around the belief that a solar day is one 360 degree earth rotation when in fact it is a little bit more.
Because a full rotation and a rotation required for a full day-night cycle are not equal.
A full rotation is 360 degrees.
Over a span of a year the earth does a rotation around the sun. Try to imagine that you are standing face to face to a person. If you move behind their back, you need a 180 degree rotation to face them again. If you keep spinning around them you need another 180 degrees when you are at your starting location
This adds a 360 degree rotation compared to the sun. That is about one degree per day. So to achieve a full day-night cicle, you need 361 degrees of rotation.
Try this demonstration. Have a friend stand in the middle of a room. You stand four or five feet from your friend and face your friend. Now, look to the wall behind your friend so that you can tell when you have turned one time. Start to walk a circle around your friend. Walk 1/4 of the way around your friend. Turn as you walk until you face the wall again. You have completed one revolution, turning 360 degrees. Are you facing your friend? No, you need to turn another 90 degrees to face your friend. It works the same way with the Earth. Each day Earth needs to rotate almost one extra degree as it traces a circle around the sun so that the sun will be directly overhead again.
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