The sun’s permanent position in the sky, plus the fact that the Earth and other planets revolve around it, can make it appear to be static and not moving or rotating.
Yet we have known that the sun rotates since the 17th century. Like the majority of planets in the solar system, this rotation is counterclockwise, but in addition to being significantly slower than the rotation of the Earth, the rotation of the sun is much more complex.
How do we know the sun is turning
The discovery that the sun rotates goes back to the time of Galileo, according The British Library (opens in a new tab). Along with many of his contemporary earlier astronomers, Galileo had observed dark patches of the sun that we now call sunspots and understand to be important parts of the solar cycle.
Galileo also noticed something else. He found that these dark spots seemed to move, disappearing and returning as he observed the sun with his telescope.
In 1612, the first scientist wrote: “It is also manifest that their rotation revolves around the sun…to me it seems more probable that the movement is of the solar globe than of its surroundings”, according to the book “Discoveries and Opinions “. of Galilee’ (opens in a new tab)(Doubleday, 1957).
Using sunspots, he discovered that the sun rotates, which is pleasantly ironic given that those cool dark spots on the surface of the sun are an artifact of that rotation.
To this day, astronomers and solar scientists use sunspots and other features on the surface of our star to measure its rotation. Yet there is more to learn about the rotation of the sun. Mainly, how different it is from the rotation of our planet.
Is the rotation of the sun different?
While Earth and the other inner planets are made of solid rock, the Sun is an ultra-hot ball of dense ionized gas – mostly hydrogen and helium – called plasma.
This means that the way it rotates is different from that of our planet, Mars, Venus and Mercury.
The sun undergoes something called differential rotation. This means that its rotation takes place at different rates depending on where you look at the star.
“Since the sun is a ball of gas/plasma, it doesn’t have to spin rigidly like solid planets and moons do,” according to (opens in a new tab) Nasa. “The source of this ‘differential rotation’ is a current area of research in solar astronomy.”
By moving from the poles of the sun to its equator, the rotation time of this plasma zone decreases. The poles complete one rotation in 35 days, while the area just above the equator completes one rotation in just 25 days. This means that no area of the sun completes an orbit as quickly as our planet.
However, the differences in rotation rates on our star are not isolated to its surface. The layers of the sun’s interior also spin at different speeds, with the inner regions actually spinning more like the solid bodies of the inner solar system.
Astronomers estimate that the sun’s core actually spins as fast as once a week, four times faster than its surface and middle layers, according to NASA’s Solar and Heliospheric Observatory (SOHO) page. (opens in a new tab). This has led solar scientists to intensely study the effects resulting from the different rotation rates in our star.
This type of rotation is not unique to the sun or even to stellar bodies. The gas giants Jupiter and Saturn also experience differential rotation. This is not surprising given their gas composition. The ice giants Uranus and Neptune also have differential rotation – all spinning faster at their equators than at the poles.
Why does the sun turn?
The counterclockwise rotation of the sun and the counterclockwise rotation of the entire solar system (except two planets) result from its formation about 4.5 billion years ago.
At this point in the history of the universe, the solar system was nothing more than a giant rotating disc of gas and dust. NASA Science suggests (opens in a new tab) that an exploding star caused it to collapse forming a solar nebula.
At the center of this nebula, our sun formed by incorporating 99% of the available matter with the outer dust clumps forming the planets. But, he incorporated something else too.
“The rotation of the sun is due to the conservation of angular momentum,” said a scientist from the National Radio Astronomy Observatory (NRAO). Jeff Mangum said (opens in a new tab). “This means that the gas cloud from which the sun formed had residual angular momentum that was transmitted to the sun as it formed, giving the sun the rotation we observe today.”
Find out how NASA and ESA study the sun’s core, including how fast it spins on NASA’s SOHO page (opens in a new tab). Additionally, you can read more about solar system rule breakers Venus and Uranus and their retrograde rotation on the Science Alert website. (opens in a new tab).
“Galileo’s Sunspot Letters (opens in a new tab)“. The British Library (2022).
“The solar rotation varies with latitude. (opens in a new tab)“. NASA (2013).
“Discoveries and Opinions of Galileo (opens in a new tab)(Doubleday, 1957).
“ESA and NASA’s SOHO Reveal a Fast-Spinning Solar Core (opens in a new tab)“. NASA (2017).
“Our Solar System”. NASA science, solar system exploration (opens in a new tab) (2021).
“Why does the sun turn?”. National Radio Astronomy Observatory (opens in a new tab) (2020).