Ask Dr. Universe: As we orbit the sun, it moves through the Milky Way

Washington State University

Dr. Universe: Does the sun orbit anything? – Kingston, 11, Illinois

Dear Kingston,

When we think about orbits, we usually picture the Earth zooming around the sun. But does the sun just sit there? Or is it on its own journey?

I asked my friend Guy Worthey. He’s a space scientist at Washington State University.

He told me that an orbit happens because the gravity from something big pulls on a moving object. The sun has lots of gravity because it’s ginormous compared to Earth. So, that gravity pulls on the Earth and holds us in orbit.

But our sun isn’t the only star. It’s one of many, many stars in the Milky Way galaxy. Scientists think there could be as many as 400 billion stars in the whole Milky Way. Lots of those stars have planets that orbit them. Just like our planet orbits our star.

The Milky Way galaxy is shaped kind of like a frisbee. Our sun is about two-thirds of the way to the edge of the frisbee. So, there are tons of stars between the center of the galaxy and our sun.

“Gravity comes from mass, and stars have mass,” Worthey said. “The Milky Way collectively weighs a lot, so it’s got gravity, and the sun orbits around it. We’re kind of in the middle of it, though, so it’s a little bit strange.”

Since our planet orbits around the sun, we go with it as it orbits around the Milky Way’s center. Our whole solar system does.

It takes the Earth one year to orbit all the way around the sun. But the sun’s path around the Milky Way is much bigger. It takes about 250 million years for the sun to make a full orbit around the galaxy – even though the sun is traveling more than 500,000 miles per hour.

Worthey told me that the last time our solar system was in this same spot in the galaxy, it was the Triassic era on Earth. That was way before humans existed. Back then, dinosaurs were wandering around. The first mammals were just starting to evolve.

So, is the Milky Way just sitting there? Definitely not. It’s zooming along at more than 1 million miles per hour. The Milky Way is moving because all the other galaxies in the universe have been pulling on it for 14 billion years.

One of those galaxies – called Andromeda – is heading toward the Milky Way, too. In about 4 billion years, scientists think they will crash into each other. But even if we were around for that, we wouldn’t notice it. The stars in the galaxies are super far apart, so they won’t bonk into each other. Our whole solar system will probably be tossed a bit farther from the center of the Milky Way – but everything will just keep on spinning.

I guess we’ll have to wait and galax-see.

Sincerely,

Dr. Universe

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