Where do those extra four minutes go every day?

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The Earth fully rotates in 23 hours and 56 minutes. Where do those extra four minutes go??

I know the answer is supposedly leap day, but I still don’t understand it from a daily time perspective.

I have to be up early for my job, which right now sucks because it’s dark out that early. So every day I’ve been checking my weather app to see when the sun is going to rise, and every day its a minute or two earlier because we’re coming out of winter. But how the heck does that work if there’s a missing four minutes every night?? Shouldn’t the sun be rising even earlier, or later? And how does it not add up to the point where noon is nighttime??

It hurts my head so much please help me understand.

In: Earth Science

17 Answers

Anonymous 0 Comments

Ok putting together some of these responses, I think the main idea is that we don’t define 24 hours as the time it takes for the earth to spin exactly 360 degrees, but instead as the time it takes for the sun to re-appear in the closest position in the sky from one day to the next. Therefore the 4 minute time difference is irrelevant to daily timekeeping with respect to the sun. (?)

Anonymous 0 Comments

A sidereal year is 365.256363004 days. A tropical year is 365.256363004 days. A sidereal year is the time it takes for the Earth to return to the same position in relation to a certain star (the Point of Aries). A tropical year is 365.24219 days. A tropical year is the time it takes the mean position of sun to advance 360 degrees. This is what the calendar is based on.

Leap years are added to correct for the difference of the odd length of the year compared to an integer number of days. We add an extra day to the year every 4 years, unless the year number is evenly divisible by 100, then an extra day is not added, unless the year number is evenly divisible by 400, then an extra day is added after all.

Thus:

1996 was a leap year, it follows rule 1

1900 was not a leap year, it follows rule 2

2000 was a leap year, it follows rule 3

This system has been working for the last about 500 years. There is a small error but it will not amount to a full day until about 3800 AD.

Anonymous 0 Comments

There are plenty of other great replies in here, but I thought I’d add a gif that shows what others have already described really well:
https://imgflip.com/gif/3o07r3

Anonymous 0 Comments

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Anonymous 0 Comments

A nominal solar day (say sunrise to sunrise) is 24 hours. If you time when a star rises each day it’s 23 hours, 56 minutes. That’s called a sidereal or star day. A given star will rise 4 minutes earlier every day, or about 1/2 hour a week, or 2 hours a month. This is why the sky shifts and changes over the course of the year–if you look at the sky before sunrise in winter, it’s the same stars you’ll see 6 months later in the evening sky (12 hours timewise), because we’ll have gone halfway around the sun.

Conversely the bright stars of winter you see now in the evening sky will be in the morning sky come summer. And as mentioned, it’s all because of Earth’s orbit around the sun, and our point of view shifting that tiny bit day by day over the course of the year.

Anonymous 0 Comments

Look up 1752, I think the year was? There’s a September where 11 whole days just *poof* vanished. VSauce did a video on this very subject.

Anonymous 0 Comments

It’s not leap day.

If the earth weren’t spinning at all, the sun would still move across the sky because the earth is going around the sun — a day would be the same length as a year. The sun would move about 1 degree East per day, so it’d be going backwards.

We spin the same direction we orbit the sun (counter clockwise if you’re looking down from the north pole), so in the time we’ve made a full rotation, we’ve also moved about 1/365^th of our orbit around the sun. That means the sun is about a degree “back” from where we’d expect it to be. So we need to rotate an extra degree, which takes about 4 minutes.

Or another way to look at it… In a year, we spin ~366.25 times, not 365.25. But moving around the sun “unwinds” one of those spins. That unwound day is spread across the days of the year. 1440 minutes in a day, split among 365 days, is about 4 minutes.

Anonymous 0 Comments

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Anonymous 0 Comments

Why doesn’t the sun move 4 minutes per day? Because the stars do! The earth spins once every 23h 56m compared to distant stars. But the earth also orbits around the sun. So during that time it’s also moved along its orbit by one day. So it needs an extra 4 minutes of spin for you to see the sun in the same place in the sky. And this is why the stars move 4 minutes per day. And why the stars have seasons. Each part of the year the night side of the earth is facing outward from the solar system in a new direction.

Anonymous 0 Comments

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