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January 14, 2019

Every object in the solar system is orbiting something else. Moons orbit planets, for example, and planets orbit the Sun. And even the Sun goes around something: the barycenter of the solar system.

As the Moon goes around Earth, it doesn’t orbit the center of our planet. That’s because both Earth and the Moon have mass — they weigh something. So both of them orbit the center of mass of the combined Earth-Moon system — a point known as the barycenter. Because Earth is the heavier object, the barycenter of the system is within the body of Earth itself.

The same thing applies to Earth and the Sun. Since the Sun is much more massive than Earth, the barycenter of the Earth-Sun system is deep within the Sun. In fact, the only planet with a barycenter outside the Sun is Jupiter, the solar system’s biggest planet.

Since the Sun has eight major planets and a whole bunch of smaller objects, they combine to create a barycenter for the entire solar system. Its exact location varies depending on how the planets are aligned. It can range from close to the Sun’s heart to far outside the Sun.

Moving around that point causes the Sun to “wobble” a bit. Astronomers can find planets around other stars by looking for a similar wobble. That technique hasn’t yielded many discoveries so far. But the Gaia space telescope may be able to find lots of worlds that way — watching as a star wobbles around the barycenter of its own planetary system.

Script by Damond Benningfield

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