# Are all days exactly 24 hours?

A solar day on Earth lasts around 24 hours. The Earth's orbit, on the other hand, is elliptical, which means it is not a complete circle. That means that some solar days on Earth are a few minutes longer and some are a few minutes shorter than 24 hours. A sidereal day on Earth lasts roughly precisely 23 hours and 56 minutes. However, since the planet's axis is tilted with respect to its orbit, different parts of the surface experience night for varying lengths of time.

The length of a day on other planets in our solar system is varied. On Mars, for example, the average day is 687 minutes long, while on Jupiter it is 10 hours and 37 minutes long.

On Earth, when it is dark outside, the sun has already gone down from view. When it is light out, then it is still daylight out here on Earth, but because the sun is going down elsewhere, it will be dark where it is daytime somewhere else.

Days get longer as we go farther from the Sun. On Mars, for example, the solar day is about 39 minutes longer than on Earth. So if there were any Martians watching the sun set for us, they would see it rise again sooner than we do!

Days get shorter as we go toward the Sun. During a total solar eclipse, the Moon passes between Earth and the Sun, blocking its rays.

## Why do our clocks have 24 hours in a day if the Earth rotates once every 23 hours and 56 minutes?

If we genuinely defined a day as one complete revolution of the Earth on its axis—a 360-degree spin—a day would be 23 hours, 56 minutes, and 4 seconds. As a result, the Earth must spin an additional degree each day in order to re-align with the sun. This extra rotation is called "obliquity" and it's what causes the daily cycle of light and darkness.

The earth's axis of rotation is not exactly perpendicular to its surface, but rather leans slightly toward either the north or south pole. The angle between the axis and the planet's equator is called "precession". Because of this wobble, after approximately 26,000 years the line up of the earth and the sun is no longer directly over a spot of land, but rather at some point around the world. At that time, all local noon times will have shifted relative to today. After another 1,000 years or so, everything will be out of alignment again.

This odd phenomenon has nothing to do with Earth's orbit around the sun, which takes approximately 365 days (almost 22 hours per day). Instead, it's due to the fact that the earth's core is not solid but rather made up of a fluid mixture that includes molten iron. This magnetic core causes the earth's orientation to change over time because it's pushing against itself and rotating at a different rate than its surrounding matter.

## Is a day on Earth shorter than 24 hours?

A day on Earth will be 0.05 milliseconds shorter than the usual 86,400 seconds that comprise a 24-hour period, according to the scientists. For the past 50 years, the globe has taken fewer than 24 hours to complete one spin, according to calculations. The reason: Ice is accumulating at both the North and South Poles.

This reduced amount of time means that people living at either pole would get only 3996 minutes (or 8 hours and 56 minutes) of daily sunlight during the winter season and 3995 minutes in the summer. A year would pass quickly for them because only about 12 months would have passed on the average world clock speed prior to 2003.

The slow down was first noticed by scientists using satellites to measure changes in the distance between stars. They found that although the number of days in a year remained constant, the distance between some stars increased by as much as 2 percent more than expected. This indicated that not only was the amount of daylight changing, but so was nightfall. Since midnight comes very soon after noon at the North Pole, it follows that a day there is getting shorter.

At the South Pole things are just the opposite. Night falls very late there, so the shortening of daytime at the North Pole is making night fall early there, too. That's why days are getting longer at the South Pole even though winter is coming.