Why does the Earth spin?
–Morven, 8, Dundee, Scotland; Judith, 9, Sabah, Malaysia; Mara, 11, USA
Dear Morven, Judith, and Mara:
No matter how still we stand, or if we’re in Scotland, Malaysia, or the United States, we are always spinning. Our Earth spins at a constant, very fast speed as we make a trip around the sun.
But it’s not just the Earth that spins, said my friend Guy Worthey, an astronomy professor at Washington State University. The moon, the sun, and almost all the other planets spin, too.
Your question actually has a lot to do with our early solar system. Scientists think the solar system started out as a kind of giant pancake, Worthey said.
Not like a pancake you’d eat for breakfast, of course. It was more like a giant pancake-shaped cloud of gas and dust. The pancake was a unit, with all parts of it spinning in the same direction, Worthey explained.
“When the planets started to form out of this big mass of gas, they shared not only the same mix of material, but also a sense of spin,” he said. “Like little whirlpools in a bigger whirlpool.”
The Earth has been spinning for billions of years, but it’s also been slowing down ever so slightly. Some scientists are interested in tracking this, too. They’ve found that the spin slows just a fraction of a second each year. If the Earth keeps this up, it would take trillions of years before it ever stopped spinning,
The length of a year, 365.24219 days, which is how long it takes the earth to travel in a huge circle around the sun, is not changing very much. The length of a year is different depending on how a planet orbits in a huge circle around the sun.
Our Earth spins around on its axis, a kind of imaginary pole that runs through the planet from north to south. The Earth spins all the way around its pole to make one complete turn each day, or 24 hours.
But if you were to visit Venus, one day would last as long as 243 Earth days. Venus spins much slower than Earth. Scientists think that an object might have hit Venus and knocked it around a bit after the solar system formed, slowing its rotation. Uranus is another planet that spins in its own unique way. It’s got an unusual tilt that makes it spin on its side.
Our Earth also has a tilt. As it spins, it doesn’t sit upright on its axis. The imaginary pole that runs through the middle sits at an angle of 23.5 degrees compared to solar system north. This tilt makes it so that some parts of the planet get different seasons.
It’s exciting to know curious cats from all around our world are stopping to wonder about our Earth’s spin. Now, let me spin a question back to you. No matter how still we stand, we are spinning. But perhaps you’ve noticed you aren’t getting dizzy or flying off the planet. Why might that be? Send me your thoughts at Dr.Universe@wsu.edu.
Ask Dr. Universe is a science-education project from Washington State University. Submit your own question at http://askDrUniverse.wsu.edu.