# Is a day 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 keeps changing orientation relative to the Sun, even this average solar day will eventually change if we waited long enough.

An astronomer might say that the solar day is actually equal to 24 hours plus 6 minutes. The extra 6 minutes allows for daylight saving time (which does not apply everywhere on Earth) as well as leap seconds.

But what about other stars? What is their solar day like? The answer depends on the star in question. Some massive stars such as our Sun will fuse hydrogen into helium in their cores over many millions of years. For these stars, the solar day is just like here on Earth: It takes 24 hours to go around once. Less massive stars such as the red dwarf Gliese 832 have exhausted their hydrogen fuel supply billions of years ago. These stars are left with nothing but a cold solid core made of iron and nickel. They also have very small diameters compared to the size of our Sun; thus they do not emit much light.

For these stars, the solar day is almost identical to the astronomical night: It takes nearly 24 hours to go from sunrise to sunset.

## What determines how long a day is?

A day is roughly the time it takes the Earth to complete one rotation around its axis, which takes around 24 hours. A solar day is the time it takes for the sun to reach its greatest position in the sky two times in a row. Because the earth orbits the sun, each day is always longer than the previous one. The amount of time that has passed since midnight was 0 hours is called "time of day". Time of day is divided into four periods: morning, noon, evening, and night.

Time keeps changing throughout your day. If you ask someone what time it is, they will probably tell you the correct time but it might be different a few minutes later. This is because the Earth's rotation is not exactly constant. When a city such as New York moves its clock forward by 1 hour, people in other parts of the world will see that it's now 10:00 instead of 9:00. As a result, there are different times listed for the same moment at different places on Earth. The best reference point for keeping track of time is the sun. So far this afternoon, for example, it has been about 15 degrees north of the equator. The sun will be at approximately this angle every 3 hours and 48 minutes during mid-September.

The length of a day is calculated from the number of whole cycles (24 hours) that have elapsed since midnight.

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

A day would be 23 hours, 56 minutes, and 4 seconds if we genuinely defined it as one complete revolution of the Earth on its axisâ€”a 360-degree spin. As a result, the Earth must spin an additional degree each day in order to re-align with the sun. This extra rotation is what gives us another hour every day.

The Earth's axis is not exactly perpendicular to its surface, so this hour difference is not exact. But over time, it adds up. After 100 million years or so, the planet will have rotated through about 5 degrees more than midnight, and the night will then begin at around 2 a.m. Rather than waiting for that moment when the stars come out again, people then start their days at noon.

This is why our clocks run fast by half past six in the evening and slow by half past four in the morning. The idea was first proposed by Sir Isaac Newton in 1664, but he may not have known about global warming yet!

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

A day on Earth will be 0.05 milliseconds shorter than the typical 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: The Earth is slowing down because it's falling into darkness at its midpoint.

This isn't the first time this has been calculated. In 1969, scientists estimated that a day was getting shorter by another half-millionth of a second every year. They came to the same conclusion then as now: That meant that within a few decades, a day would shrink by enough seconds for us to need an extra hour of sleep each night.

In other words, go ahead and set your alarm clocks 30 minutes earlier next week!

##### Audra Jones

Audra Jones has been practicing yoga and spirituality for over 30 years. She has always had a deep interest in the healing practices of ancient cultures and how to apply them today. Audra is skilled at using her intuition and understanding of energy to create sacred spaces that promote healing. Her clients find solace in their sessions with her, as she helps them find peace within themselves through meditation techniques, calming imagery, aromatherapy, sound therapy, essential oils, etc.

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