It is common knowledge that the Sun is the center of the Solar System. Around him, planets orbit, along with a thick asteroid belt, a few meteor fields, and a handful of far distant comets.
But that is not the whole story.
“Instead, everything orbits around the center of mass of the Solar System,” James O’Donoghue, a planetary scientist at the Japanese space agency JAXA, recently explained on Twitter. “Even the sun”.
That center of mass, called a barycenter, is the point on an object where it can be perfectly balanced, with all of its mass evenly distributed on all sides. In our Solar System, that point is rarely aligned with the center of the Sun.
To demonstrate this, O’Donoghue created the animation below, which shows how the Sun, Saturn, and Jupiter play tug-of-war around the barycenter, dragging our star in tiny looped orbits.
In his spare time, O’Donoghue makes animations to show how the physics of planets, stars, and the speed of light work.
“The natural thought is that they orbit the center of the Sun, but that rarely happens,” he said.
“It is very rare for the center of mass of the Solar System to align with the center of the Sun.”
The movement of the Sun is exaggerated in the video above to make it more visible, but our star rotates millions of kilometers around the barycenter, sometimes passing over it, sometimes moving away from it.
Much of that movement comes from Jupiter’s gravity. The Sun represents 99.8 percent of the mass of the Solar System, but Jupiter contains most of the remaining 0.2 percent. That mass attracts the Sun very gently.
“The Sun actually orbits Jupiter slightly,” O’Donoghue said.
Within the Solar System, planets and their moons have their own barycenter. Earth and Moon do a simpler dance, with the remaining center of gravity inside Earth. O’Donoghue also made a video of that:
The animation also shows how Earth and Moon will move in the next three years, in 3D. (The distance between Earth and the Moon is not to scale).
Pluto and its moon, Charon, do something similar, but with a unique twist: the barycenter is always outside of Pluto.
Therefore, each planetary system orbits an invisible point, including the star or planet that appears to be in the center. Barycenters sometimes help astronomers find hidden planets that surround other stars, as they can calculate that the system contains a mass that they cannot see.
“The planets orbit the Sun, of course,” said O’Donoghue. “We are being pedantic about the situation.”
This article was originally published by Business Insider.
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