As we go about our daily lives, it’s easy to forget that we’re all hurtling through space at incredible speeds. Earth is constantly in motion, rotating on its axis and orbiting around the sun. In fact, we’re all living on a fast-moving spacecraft. But just how fast is our planet moving? What is the speed of Earth in space?
The answer is surprisingly complex, as the exact speed varies depending on the reference point. Questions about how fast the Earth, or anything, is moving are incomplete unless they also ask, “Compared to what?” Without a frame of reference, questions about motion cannot be fully answered. For example, when we say a car is going at 120 km/h, we mean that it travels 120 km across the Earth in one hour, ignoring the fact that the Earth itself is also moving.
Calculating the Speed of Earth in Space
The Earth is rotating on its axis and orbiting the Sun. Additionally, the Sun, along with our entire solar system, whirls around the center of our galaxy, the Milky Way. Furthermore, our galaxy and neighboring galaxies are rushing towards a structure called the Great Attractor, a region of space roughly 150 million light-years away from us.
The Great Attractor, with a mass 100 quadrillion times greater than our Sun and spanning 500 million light-years, is composed of both visible matter that we can see and the so-called dark matter that we cannot.
So, even when resting in your armchair, you’re flying through space faster than the fastest human-made object ever built. But how fast, exactly?
1. The Rotational Speed of Earth
The Earth is 24,900 miles (40,000 kilometers) in circumference at the equator. It takes 24 hours for the Earth to complete one full rotation. Therefore:
24,900 miles / 24 hours = 1,037 mph (1,666 km/h)
The rotational sped of Earth
This speed is the highest at the equator and decreases as you move toward the poles. At the poles, the rotational speed is effectively zero, as you are rotating in place once every 24 hours. For instance, if you are in South Florida, you are moving at approximately 1,000 miles per hour (1,610 km/h or 0.447 kilometers per second). This high rotational speed is one of the reasons NASA launches rockets from Florida.
2. The Orbital Speed of Earth around the Sun
Earth lies at an average distance of 149.6 million kilometers (93 million miles) from the Sun. It takes 365.256 days to complete one orbit, known as a sidereal year, which is measured relative to the stars. This period is approximately 20 minutes longer than the tropical year due to the precession of the Earth’s axis. During this time, Earth travels a distance of about 940 million kilometers (584 million miles).
584,000,000 miles / (365×24 hours) ~= 67,000 mph
The orbital speed of Earth around the Sun
Therefore, the orbital speed of Earth averages about 30 km/s (30 kilometers per second, 108,000 km/h or 67,000 mph). At this speed, Earth could cover its own diameter in just seven minutes and the distance to the Moon in approximately four hours. For comparison, Apollo 11 took approximately 76 hours to travel from Earth to the Moon.
3. The Sun’s Motion
Our Sun’s motion also affects the speed of Earth in space. The Solar System, located near the edge of the Milky Way, orbits the galactic core at a distance of about 25,000 light-years from the center. By measuring the speed of other galaxies moving towards or away from us, we can estimate our own orbital speed: the Milky Way completes one rotation approximately every 250 million years.
This gives the Solar System an average speed of around 230 kilometers per second (514,000 mph or 828,000 km/h). However, we can’t simply add this to Earth’s speed around the Sun because our motion is circular. Therefore, Earth’s speed around the galaxy varies between 447,000 mph and 581,000 mph (720,000 km/h to 936,000 km/h), depending on the time of year.
4. The speed of the Milky Way Galaxy itself
Today, some 13 billion years after the Big Bang, space has expanded significantly. The initial flash from the Big Bang has stretched into longer, lower-energy waves, such as microwaves and radio waves. These waves, now called the Cosmic Background Radiation (CBR), still fill the universe just as they did at the time of creation.
In the late 1940s, physicists predicted the existence of this background radiation, but without the equipment to detect it, the prediction was forgotten. In the mid-1960s, Arno Penzias and Robert Wilson, scientists at Bell Laboratories, accidentally discovered the CBR while working on communications satellite technology. Their discovery, later confirmed by other telescopes and rockets, earned them the Nobel Prize in Physics as it provided the most direct evidence for the Big Bang.
The CBR serves as a “frame of reference” for the universe, allowing us to measure our motion relative to it. In 1989, the COBE satellite was launched to measure this radiation, revealing that Earth is moving at 600 kilometers per second (1.34 million miles per hour) relative to the CBR. Our motion is roughly in the direction of the constellations Leo and Virgo, likely due to a massive concentration of matter in that area, known as the Great Attractor. This concentration of gravity pulls the Milky Way and neighboring galaxies in that direction.
Summary: The Speed of Earth in Space
Overall, the Earth’s speed in space is around 370 kilometers per second (1,332,000 km/h or 827,666 mph) relative to the Cosmic Microwave Background (CMB). This speed varies depending on our position in the Earth’s orbit around the Sun and the Milky Way.
This speed is less than the Milky Way’s speed relative to the CMB toward the Great Attractor because the Sun is moving in the opposite direction. The difference in these speeds (600 km/s – 230 km/s) results in Earth’s speed of 370 kilometers per second relative to the CMB.
The overall speed of Earth in space ~= 370 kilometers per second (1,332,000 km/h or 827,666 mph)
Earth’s speed in space is around 370 kilometers per second (1,332,000 km/h or 827,666 mph) relative to the Cosmic Microwave Background (CMB)
Video: The Earth’s Relative Cosmic Velocities
Planetary scientist Dr. James O’Donoghue published a video showing the relative cosmic velocities of planet Earth and the speeds to scale.
O’Donoghue says “The speed of light is 350 times faster than all these velocities combined”.
Sources
- Cover image: Casey Horner on Unsplash
- How fast is the Earth moving? on Scientific American
- How fast is the Earth traveling through space? on Urban Astronomer
- How fast are you moving through the universe right now? on the Brain Stuff Show website
- Earth’s orbit on Wikipedia
- How Fast Are You Moving When You Are Sitting Still? on the Astro Society website
- Great Attractor on Wikipedia
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