How Fast Does the Earth Spin?

Key Points

• Earth spins at about 1,037 mph (1,670km/hr) at the equator.
• Earth orbits the sun at a speed of about 2.6 million kilometers daily, equivalent to around 107,460 km/hr.
• Earth’s rotation is slowing down, but the recent slight increases in rotational speed should be treated as normal fluctuations.
• Melting polar ice caps, the Chandler wobble, and changes in Earth’s inner core could be contributing to the Earth’s faster pace.

It might feel like you’re completely still, but Earth carries us along as it spins around its own axis. As we rotate, we also orbit the sun. It takes about one sidereal day — to be precise, 23 hours, 56 minutes, and 4 seconds for Earth to complete one spin on its axis. However, a whole trip around the sun takes 365.25 days. 

So, how fast is the Earth moving? Let’s talk about it!

Earth’s Rotational Speed

Earth is the only planet that supports life and is the most dense. It has a circumference of about 40,075 kilometers at the equator. So, if we divide this distance by the time it takes to complete one rotation, it means our home planet spins at about 1,037 mph (1,670km/hr).

As you move far from the equator, the rotational speed is calculated using cosine, a trigonometric function of the latitude found in most scientific calculators. For example, at 45 degrees latitude, north or south, Earth spins at about 733 mph (1,180km/hr). 

The cosine of 45 degrees is 0.707; therefore, to calculate the speed at which Earth is rotating at this latitude, multiply the cosine (0.707) by 1,670 km/hr or 1,037 mph. Note that the farther you go to the south or north, the slower Earth’s rotational speed will be. 

The rotational speed is not consistent across the planet. As you move to the poles, the circumference gets smaller, and the speed decreases. That explains why Earth travels slowest at the top and bottom and fastest in the middle.

Earth’s Orbital Speed

To calculate Earth’s orbital speed, you will need to know the duration it takes the planet to orbit the sun and the distance it covers to travel around it. Earth takes 365.25 days to orbit the sun. The distance from Earth to the sun is about 150 million kilometers, which represents the radius. So, we have to calculate the circumference (i.e., the distance planet Earth covers to orbit the sun).

Circumference = 2 x 3.14 x r (150 million kilometers), meaning to orbit the sun, Earth covers about 942 million kilometers in one year. Orbital speed is the quotient of the distance covered and the time taken. Therefore, Earth orbits the sun at a speed of about 2.6 million kilometers daily, equivalent to around 107,460 km/hr.

What Makes Earth Spin?

Scientists believe that Earth was formed spinning and inherited its angular momentum from its parent material, a cloud of gas and dust. However, we first need to understand how our solar system was formed to answer the question of what makes planet Earth spin. 

Around 4.5 billion years ago, a giant cloud of gas and dust known as the solar nebula collapsed, forming a disk-shaped rotating matter. Gravity pulled the swirling gas and dust, and the materials began to clump together, forming our solar system and everything in it. 

Most of the turbulent material was pulled toward the center, forming the sun. Other materials collided and stuck together to form planets, including Earth. The moon and asteroids were also formed thanks to the nebula supervona. The cloud of gas and dust was already moving in a circular motion, so all the formed planets continued to rotate on their own axis, still to date.

Each of these planets has its unique rotational velocity. This is because the material that collided to make up each planet moved at different speeds during the formation. So, every planet was left with whatever velocity it gained or lost at its last interaction. That’s how our planet began to spin.

Discovering Earth’s Rotation

Before the 16th century, there were tons of speculations about Earth’s movement. Many believed Earth was at a standstill and the sun, stars, and moon were in motion. However, the interpretations took a different turn in 499 BC when Aryabhata, an Indian astronomer, suggested that Earth rotates on its own axis. In 1543, Nicolaus Copernicus presented a convincing model (heliocentric theory) showing that Earth spins on its axis and orbits the Sun.

The theory was later confirmed by French physicist, Leon Foucault, in 1851. He used a pendulum to demonstrate how Earth rotates about an axis. His experiment was a turning point in the history of astrometry. It gave clear evidence of Earth’s rotation, which helped dispel lingering doubts that were based only on astronomical observations.

Heliocentric theory allowed room for scientific experiments and discoveries, changing our scientific perspective of the universe. Today, we know that all planets orbit the sun and rotate their own axis. 

Interesting Facts

It takes Earth one solar day — 24 hours (which is about 3 minutes and 56 seconds longer than the actual rotation period) — to move about its axis and have the sun show up in the same position in the sky. During the daytime, the sun appears to move across the sky, while in reality, it is our planet spinning from west to east. As it rotates, half of it faces the sun, and the other faces away from the sun, which explains the existence of daytime and nighttime.

Note that the length of daytime and nighttime varies depending on where you are and the time of the year. Places near the equator may experience 12 hours of night and 12 hours of daytime. However, as you move toward the north and south poles, you will notice variations in the length of day and night, meaning daytime may be longer than nighttime and vice-versa.   

Has Earth’s Rotation Ever Changed?

As improbable as it may sound, Earth’s rotation is slowing down. Six hundred million years ago, our home planet’s rotation was steady, and days were shorter than today. An Earth’s day was 19.5 hours constant.

However, Earth has experienced a slight increase in rotational speed in recent years. In 2020, it recorded 28 shortest days since the 1960s and continued to spin faster through 2021 and 2022. On June 29^th, 2022, it set a record for pulling off a full rotation 1.59 milliseconds ahead of schedule, and this remains the fastest-ever rotation since 1970. 

Earth’s increased rotational speed shouldn’t be a cause for concern, scientists say. They claim that our planet has experienced shorter days in the past. As a result, the 2020-2022 slight increases in rotational speed should be treated as normal fluctuations. 

Points of Concern

Perhaps we need to ask ourselves if these shifts impact our daily lives. The last time a leap second was added was in 2016 to compensate for the variations between the actual atomic time and Earth’s slower rotation. Recent discrepancies have resulted because Earth has been rotating faster than usual. So, should timekeepers subtract a leap second to help synchronize the Universal Time and International Atomic Time?

The shortening of Earth’s days could majorly affect our clocks, but then a negative leap second could help sync our clocks. On the contrary, it can wreak havoc on the digital world. Systems that require an uninterrupted flow of time, such as software, satellites, communication networks, and trade systems, could experience serious technical problems.

As a result, giant companies like Meta and Google have demanded for leap seconds to be scrapped. On November 18th, 2022, an international group of experts resolved to retire the practice by 2035. Luckily, predictions for the next 2,000 years show that if we stick to using International Atomic Time, we won’t encounter any serious issues. By then, we will have discovered better solutions to remediate clock-related glitches.  

Reasons Why Earth is Speeding Up

Scientists say that melting polar ice caps and glaciers could be to blame for the Earth’s faster pace. They also claim that the Chandler wobble could affect how fast our planet rotates. Moreover, recent findings suggest that the variations in the length of the day could also be linked to the changes in Earth’s inner core.

Surprisingly, there is no exhaustive explanation of what is speeding us up. How the inner core rotates has been a matter of debate among many. In this context, more studies must be carried out to help unveil the mysteries of Earth’s core.

The Debate About Earth’s Core

Data stretching back to the 1960s indicate that the inner core was at a standstill in the 1970s. From then, it started to spin gradually faster, overtaking the speed of Earth’s rotation. It began to decelerate at some point and appeared to have been at a standstill between 2009 and 2011. It’s now said to have started spinning again.

In their study, Pro. Xiaodong Song and Dr. Yi Yang of Peking University claimed that the inner core will accelerate, then decelerate and reach a standstill, most likely in the 2040s. These Chinese scientists used the changing patterns of Earth’s inner core over the past six decades to support their claims. They further said that the inner core changes direction every 35 years.

However, John Vidale, an American seismologist, disagrees with this claim, stating that the inner core changes direction after every 6 years or so. He based his analysis on the late 1960 and early 1970 seismic waves. He also believes that the inner core made a significant move between 2001-2013 and has since stayed put.

Similarly, Hrvoje Tkalcic, an Australian geophysicist, seems to have different findings. He claims that the inner core cycle occurs every 20-30 years.

The bottom line is that scientists are not sure what’s causing our home planet to spin faster than usual. However, they can only predict that the speed-ups are temporary and will slow down in the future. So, we may have no reason to worry.

Summary Table

The image featured at the top of this post is ©Dima Zel/Shutterstock.com.