The Earth is a large globe, and we live on it. We live on its surface, which is called the earth. The earth is made up of several layers, the inner core, the outer core, the mantle, and the crust.

The inner core is the center of the earth where all the magnetic force that affects GPS navigation comes from. The outer core is what **causes earthquake activity**. The mantle and crust are what make up our planet’s surface.

Due to our *modern technology based almost entirely* on electronics, it has come to our attention that our planet does not rotate at a constant speed. This is most apparent when **observing 24 hour periods**– it seems that time passes more quickly during the week than on weekends!

This article will discuss how we can observe the Earth’s rotation, how we can determine its rotation rate, and why its rotation rate changes.

## The Earth moves 15,480 km every hour

The *third important fact* about the Earth is that it moves, and not just around the sun. The Earth rotates on its axis and it **also revolves around** the sun.

The speed at which the Earth moves depends on whether you are considering its rotation or revolution.

Its daily speed is 15,*480 km per hour*, which is called the circumferential speed. This is how fast the Earth rotates on its axis while making a complete revolution around the sun.

Its annual speed is almost 60,**000 km per hour**, which is called the heliocentric velocity. This is how fast the Earth moves as it orbits around the sun.

These speeds are very easy to confuse, so make sure to keep them separate in your mind.

## The distance the Earth moves in one day is 365,000 km

In one day, the Earth travels 365,000 kilometers, which is close to its diameter. This is what we call the planet’s daily velocity.

Because the Earth rotates on its *axis every 24 hours*, it covers a *greater distance every hour*. Its hourly velocity is approximately 1,* 500 kilometers per hour*.

Theoretically, if you stood still on the Earth’s surface at any given time and looked around, you would see everything moving at a speed of about 1,500 kilometers per hour. This is because you would be observing the Earth’s surface from a vantage point that was constantly moving in the opposite direction.

The planet’s daily and hourly velocities are not very large when compared to its radius. Because of this, its circumference (the length of its perimeter) changes very little due to its motion.

## The circumference of the Earth is 40,000 km

The measurement of the distance around the Earth is called the circumference. This is **usually calculated** by finding the diameter of the Earth and doubling it.

The diameter of the Earth is approximately 12,700 kilometers. Doubling this gives a circumference of 25,400 kilometers, which is very close to the actual circumference of 40,000 kilometers.

You *might notice* that this number is not a whole number of hours; this is because one day is not a *full 24 hours*. A day is 23 hours, 56 minutes and **4 seconds long**.

## Divide the circumference of the earth by its diameter

Now, let’s figure out the speed of the earth as it rotates on its axis. To do this, we’ll need to know the earth’s radius, which we mentioned earlier is around 6,000 kilometers (3,700 miles)

You can find this information online or look it up in a encyclopedia. Once you have the radius of the earth, you can calculate its circumference and thus its rotation speed.

To divide the circumference of the earth by its diameter, you need to use a **mathematical term called** an inverse function. In this case, you need to use an inverse cosine function.

The formula looks like this: Speed = Radius × 1/*24 hours × 1 hour*/60 minutes× 60 seconds/1 second.

## Multiply by 2 to get the approximate radius of earth

Now that you know how to calculate the earth’s circumference, you can use this knowledge to find the earth’s radius!

Just divide the earth’s circumference by its diameter and you’ll get the radius. The diameter is actually the longest distance from one side of the globe to the other, so this is ** pretty easy** to figure out.

Radius = circumference / diameter

For example, if the circumference of the earth is 24,000 miles and its diameter is 8,000 miles, then its radius is 6,000 miles. Pretty easy!

The earth’s radius isn’t a *whole number*, which **makes sense since** it isn’t a perfect sphere. It’s about 6,378 kilometers, or 3,963 miles.

## There may be small variations in this calculation due to gravity affecting mass distribution around the earth

Now that you know the earth’s radius, you can figure out how long it takes the earth to *make one complete rotation* on its axis. This is called one day or 24 hours.

The *earth takes 23 hours*, 56 minutes and 4 seconds to make one rotation on its axis. That’s only about 2 minutes longer than you’d expect, given this calculation!

You may have heard that the earth’s rotation is slowing down. That’s because scientists have observed changes in the planet’s gravitational field and predicted that this would slow down the planet’s rotation.

However, new research suggests that this may not be true after all. It claims that changes in the Earth’s mantle may be responsible for these fluctuations in the planet’s gravitational field.

The **researchers also noted** that such fluctuations in Earth’s **mass distribution could also change** our planet’s angular momentum, but only by 1% at most.

## This calculation is an approximation and not perfect but fairly close

Now that you know how to calculate the earth’s circumference, you can use this knowledge to figure out how long it takes the earth to make a complete rotation on its axis.

The earth has a radius of 6,371 kilometers (3,963 miles). That means the length of a circle that encloses the Earth is 6,371 kilometers. You can also think of this as the distance from the Earth’s center to its surface.

It *takes 24 hours* for the Earth to make one rotation on its axis. Therefore, one revolution = **360 degrees x 24 hours** = 7,920 degrees.

You can simplify this even more by dividing 7,920 by 360: *245 degrees per hour*.

## Radius of earth = 6,372.6km (1% difference from original measurement), which is very close!

The earth’s radius has been measured very accurately, and the current measurement is very close to the original measurement.

The original measurement was done by plane and satellite measurements, and then *calculated using mathematics*. Now, we can **use satellites** to directly measure the earth’s radius.

Satellites use geometry to calculate the earth’s radius, by measuring the distance from the satellite to the ground and adding that to its height. Then it divides that number by 360 degrees (or how many degrees in a circle) to get the radius!

There are some minor differences between the two measurements, but they are less than *one percent different*.