The Sun's fixed position in the sky, plus the fact that the Earth and other planets orbit it, can make it appear to be stationary and not moving or rotating.
We now know that the sun has rotated since the 17th century. Like most planets in the solar system, this rotation is counterclockwise, but in addition to being significantly slower than the Earth's rotation. Earth, the rotation of the sun is much more complicated.
According to the British Library (opens in a new tab), discovered that the rotating sun dates back to the time of Galileo Galilei. Along with many of his earlier contemporaries, Galileo observed dark patches of the sun that we now call sunspots and understand as important parts of the solar cycle.
Read Also: Discover The Meaning Of The Musical Term Toccata.
Galileo noticed something else too. He found these dark spots appeared to move, vanishing and returning as he observed the sun with his telescope.
In 1612, the early scientist wrote: "It is also manifest that their rotation is about 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 Galileo' (opens in new tab)(Doubleday, 1957).
By using sunspots, he had discovered that the sun rotates, pleasingly ironic given these dark cool patches 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 sun's rotation. Primarily, how different it is from the rotation of our planet.
IS THE SUN'S ROTATION DIFFERENT?
While Earth and the other inner planets are composed of solid rock, the sun is an ultra-hot ball of dense ionized gas — mainly hydrogen and helium — called plasma.
That means that the way it rotates is different than the way our planet, Mars, Venus, and Mercury do.
The sun experiences something called differential rotation. This means that its rotation proceeds at different rates depending on where you look at the star.
"Since the sun is a ball of gas/plasma, it does not have to rotate rigidly like the solid planets and moons do," according to(opens in new tab) NASA. "The source of this 'differential rotation' is an area of current research in solar astronomy."
Moving from the sun's poles to its equator, the time in which this area of plasma rotates shortens. The poles complete a rotation in 35 days, while the area just above the equator completes a rotation in just 25 days. This means that no area of the sun completes an orbit anywhere near as rapidly as our planet does.
Differences in rotation rates on our star aren't isolated to its surface, however. The layers of the sun's interior also rotate at different speeds with inner regions actually rotating more like the solid bodies of the inner solar system.
Astronomers estimate that the core of the sun actually rotates as rapidly as once a week, four times faster than its surface and intermediate layers, according to NASA's Solar and Heliospheric Observatory (SOHO) page(opens in new tab). This has led to solar scientists intensely studying the effects that arise as a result of different rotation rates throughout our star.
This type of rotation isn't 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 gaseous composition. The ice giants Uranus and Neptune also have differential rotation — all spinning faster at their equators than they do at the poles.
WHY DOES THE SUN ROTATE?
The sun's counterclockwise rotation and the counterclockwise rotation of the entire solar system (except two planets) is a result of its formation around 4.5 billion years ago.
At this point in the universe's history, the solar system was no more than a giant rotating disc of gas and dust. NASA Science suggests(opens in new tab) that an exploding star caused this to collapse forming a solar nebula.
At the center of this nebula, our sun formed incorporating 99 percent of the available matter with the outer dust clumps forming the planets. But, it incorporated something else too.
"The rotation of the sun is due to conservation of angular moment," National Radio Astronomy Observatory (NRAO) scientist Jeff Mangum said(opens in new tab). "What this means is that the gas cloud from which the sun formed had some residual angular momentum that was passed on to the sun when it formed, which gives the sun the rotation that we observe today."
