Earth is constantly moving. As it zooms around the sun, Earth also spins on its axis, like a basketball on the tip of a player’s finger.
So, how fast is Earth moving? In other words, how fast is it rotating on its axis and how fast is it orbiting the sun? To go even further, how fast is the solar system orbiting the Milky Way galaxy?
Now that your head is spinning just like Earth, let’s start with the planet itself. Earth turns on its own axis about once every 24 hours (or, to be precise, every 23 hours, 56 minutes and 4 seconds). Earth measures 24,898 miles (40,070 kilometers) in circumference, so when you divide distance by time, that means the planet is spinning 1,037 mph ( 1,670 km/h).
Meanwhile, Earth orbits the sun at about 67,000 mph (110,000 km/h), according to Ask an Astronomer, a blog run by astronomers at Cornell University in Ithaca, New York. Scientists know that by taking the distance Earth travels around the sun and dividing it by the length of time Earth takes to complete one orbit (about 365 days).
Ask an Astronomer explains the math: To calculate Earth’s distance around the sun, all scientists need to do is to determine the circumference of a circle. We know that the Earth is, on average, about 93 million miles (149.6 million km) away from the sun, and we know that it travels in a generally circular path (it’s actually more elliptical, but it’s simpler to do this equation with a circle). That distance between the sun and Earth is the radius of the circle. To get the circumference of that circle, the equation is 2*pi*radius, or 2*3.14*93 million miles. Once the circumference (the distance Earth travels around the sun in one orbit) is calculated, its orbital speed can be determined.
The solar system, which includes our sun and all of the objects that orbit it, is also moving; it’s located within the Milky Way, which orbits around the galaxy’s center. Scientists know that the Milky Way is orbiting a galactic center based on observations of other stars, said Katie Mack, a theoretical astrophysicist at North Carolina State University. If stars very far away seem to be moving, that’s because the solar system is moving compared with the relative position of those far away stars.
To bring this concept back down to Earth, “If I start walking, I can tell that I’m moving because the buildings I pass by seem to be moving,” from in front to behind me, Mack said. If she looks at something more distant, like a mountain on the horizon, it moves a little slower because it’s farther away than the buildings, but it still moves relative to her position.
By studying other stars’ movements relative to the sun, scientists have determined that the solar system orbits the Milky Way’s galactic center at about 447,000 mph (720,000 km/h).
Then there’s the entire Milky Way, which is pulled in different directions by other massive structures, such as other galaxies and galaxy clusters. Just like scientists can tell that the solar system is moving based on the relative movement of other stars, they can use the relative movement of other galaxies to determine how fast the Milky Way is moving through the universe.
Even though everything is moving all the time, living organisms on Earth’s surface don’t feel it for the same reason passengers on an airplane don’t feel themselves zipping through the air at hundreds of miles an hour, Mack said. When the plane lifts off, passengers feel the plane’s acceleration as it speeds down the runway and lifts off; that weighted feeling is caused by the plane’s quickly changing speed. But once the plane is flying at cruising altitude, passengers won’t feel the speed of hundreds of miles per hour because the speed doesn’t change.
The passengers won’t feel the speed because those passengers are actually moving at the same speed and direction, or velocity, as the airplane. There’s no relative motion — everyone sitting on the airplane is moving at the same speed as the airplane itself. The only way passengers might notice their and the plane’s movement is by looking out the window at the passing landscape.
For humans standing on the surface of our planet, they don’t feel Earth hurtling around the sun because they’re also hurtling around the sun at the same speed.
Originally published on Live Science.
livescience.com, 28 June 2021