The planet Earth on April 17, 2019. The Earth Polychromatic Imaging Camera (EPIC), a NASA camera aboard NOAA’s DSCOVR spacecraft, returns daily images of Earth from a distance of nearly 1 million miles (1.6 million kilometers). This animation shows the entire rotation of the planet on that day.
As inhabitants of Earth, it’s a natural feeling to perceive ourselves as stationary. We don’t experience the sensation of extreme speed in our daily lives. However, this perception is far from reality. We are, in fact, traveling through space at astonishing speeds.
So, just How Fast Does Earth Travel Around The Sun? The answer might surprise you and will lead us on a journey through astronomical history and modern science to truly understand our place in the cosmos.
Early astronomers, in their attempts to understand the universe, initially proposed a geocentric model. This model placed Earth at the universe’s center, with the sun, moon, and stars revolving around us. This seemed to explain daily phenomena like sunrises and sunsets. However, anomalies like retrograde motion, where planets appeared to temporarily move backward in the sky, began to challenge this Earth-centric view.
Retrograde motion, particularly observed with Mars, puzzled early astronomers. This phenomenon occurs because Earth, in its orbit closer to the sun, moves faster than Mars. As Earth overtakes Mars in their respective orbits, Mars appears to reverse its direction in the sky from our perspective before resuming its forward path once Earth has moved past.
Related: How Big is Earth? Unveiling the Size and Dimensions of Our Home Planet
Further evidence against a geocentric universe came from the observation of parallax. Parallax is the apparent shift in the position of a nearby object when viewed from different locations. Imagine holding your finger at arm’s length and observing it first with your left eye only and then with your right. Your finger appears to shift position relative to the background.
This same principle applies to stars. As Earth orbits the sun over a year, our vantage point for observing distant stars changes. By observing a star in summer and again in winter, astronomers can detect a slight shift in its apparent position due to Earth’s movement in its orbit. This parallax effect not only provided proof of Earth’s orbit around the sun but also allowed for the calculation of distances to nearby stars.
Earth’s Speed in Space: Expert Insights
To delve deeper into the intricacies of Earth’s motion, we consulted with Dr. Simon Lock, a research fellow specializing in planetary science, astrophysics, geophysics, and geochemistry at the University of Bristol.
Simon Lock
Research Fellow, School of Earth Sciences at the University of Bristol
Q&A: Unpacking Earth’s Velocity
How fast is Earth’s orbital speed around the sun?
Dr. Lock explains that Earth’s orbital speed is approximately 67,100 miles per hour (30 kilometers per second). To put this into perspective, this speed is equivalent to traveling the distance between major cities like Rio de Janeiro and Cape Town, or London and New York, in a mere three minutes. This incredible velocity underscores just how dynamic our seemingly static existence truly is.
Beyond its orbit around the sun, what other movements is Earth involved in?
Our journey doesn’t end with orbiting the sun. Dr. Lock clarifies that the sun, along with Earth and the entire solar system, is also orbiting the center of the Milky Way galaxy. This galactic orbit occurs at an even more breathtaking speed of around 447,000 miles per hour (200 kilometers per second). Furthermore, the Milky Way galaxy itself is in motion relative to other galaxies in the universe. Essentially, everything in the cosmos is in a constant state of motion, a grand cosmic dance.
How does Earth’s orbital speed compare to other planets in our solar system?
The orbital speed of a planet is dictated by its distance from the sun. Planets closer to the sun experience a stronger gravitational pull and thus must travel faster to maintain their orbit. Mercury, the innermost planet, orbits at a staggering 105,000 mph (47.4 km/s), about 1.6 times faster than Earth. Conversely, Neptune, the farthest planet from the sun, travels at a more leisurely pace of 12,200 mph (5.4 km/s), only about 18% of Earth’s speed. This variation highlights the influence of gravitational forces on planetary motion.
The Spin of Earth: A Rotation on Our Axis
In addition to its orbital motion, Earth is also spinning on its axis. The speed of this spin varies depending on your latitude.
At the equator, Earth’s circumference is approximately 24,898 miles (40,070 kilometers), according to NASA. A complete rotation, defining a day, takes roughly 24 hours. Dividing the circumference by the time it takes to complete one rotation yields a spin speed at the equator of about 1,037 mph (1,670 km/h).
However, as you move towards the poles, the circumference around Earth decreases, and consequently, the spin speed reduces. At a latitude of 45 degrees, the spin speed is roughly 733 mph (1,180 km/h). At the North and South Poles, the spin is minimal; you would essentially rotate in place over 24 hours.
Space agencies leverage Earth’s spin, particularly the higher speeds near the equator, for rocket launches. Launching rockets eastward from locations near the equator, like Florida, provides a significant speed boost, aiding missions to the International Space Station (ISS) and beyond.
Calculating Earth’s Orbital Speed: A Geometric Approach
sun appears as a glowing yellow ball of plasma.
The Sun’s fiery surface showcases intense solar activity. (Image credit: Miguel Claro)
Earth’s journey around the sun is an elliptical path, but for simplification, we can approximate it as a circle to calculate its orbital speed. Earth completes one orbit in approximately 365.25 days, which defines a year.
The average distance between Earth and the sun, known as an astronomical unit (AU), is approximately 92,955,807 miles (149,597,870 kilometers). This distance represents the radius (r) of Earth’s orbit.
The circumference of a circle is calculated using the formula 2πr. Therefore, in one year, Earth travels approximately 584 million miles (940 million km) around the sun.
To calculate speed, we divide distance by time. Dividing 584 million miles by 365.25 days and then by 24 hours gives us Earth’s orbital speed of approximately 66,627 mph (107,226 km/h), which is close to the expert-provided figure of 67,100 mph.
Related: How Fast Does Light Travel? Understanding the Ultimate Speed Limit of the Universe
The Sun and Milky Way’s Cosmic Motion
The sun, our star, is not stationary either. It orbits the center of the Milky Way galaxy at an estimated speed of 448,000 mph (720,000 km/h). Located about 25,000 light-years from the galactic center, the sun takes approximately 230 million years to complete one orbit around the Milky Way.
The Milky Way galaxy itself is also in motion, heading towards a collision with our neighboring Andromeda Galaxy in about 4 billion years. These galaxies are approaching each other at a speed of about 70 miles per second (112 km/s).
This intricate web of motion highlights that everything in the universe, from planets to stars and galaxies, is in a state of constant movement and interaction.
What If Earth Stopped Spinning? A Hypothetical Scenario
While the possibility of Earth abruptly stopping its spin is virtually nonexistent for billions of years, considering this scenario helps us understand the forces at play.
Were Earth to suddenly stop spinning, the atmosphere, still in motion at the original rotational speed, would create catastrophic winds, sweeping everything across the surface. NASA emphasizes that this scenario is improbable due to Earth’s strong gravity relative to its spin.
A gradual slowing of Earth’s rotation over billions of years is more plausible due to the gravitational influence of the sun and moon. The slowest possible rotation would result in a “sun-synchronous” state, where one side of Earth perpetually faces the sun, similar to the Moon’s synchronous rotation with Earth.
If Earth were to stop spinning altogether, the magnetic field, believed to be generated partly by Earth’s rotation, would likely disappear. This loss would eliminate the protective Van Allen radiation belts and auroras, leaving Earth exposed to harmful solar radiation from coronal mass ejections, posing significant biohazards.
Additional Resources and Further Reading
Bibliography
- New Scientist, “How fast does Earth spin?” https://www.newscientist.com/question/fast-earth-spin/
- NASA JPL, “How Fast Are You Moving When You Are Sitting Still?” 2007. https://nightsky.jpl.nasa.gov/docs/HowFast.pdf
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Elizabeth Howell
Former Staff Writer, Spaceflight (Space.com)
