# Does the Sun rotate?

The planets rotate as an after effect of their creation, the dust clouds that compressed span as they did so and the inertia has kept it rotating ever since.

It's fairly easy to prove that planetary bodies are rotating just by watching their features move across their respective horizons.

This seems less easy to discern for amateur astronomers in the case of the sun though.

Does the Sun also rotate as a by-product of it's creation? What evidence is there to support this? Does the sun have any discerning features that make it evident it is rotating?

• Why did Galileo bother? Commented Oct 16, 2015 at 15:09

Yes.

It does not rotate uniformly though, different portions have a different angular velocity (as a body made of plasma, it can get away with this).

Measuring this in theory is pretty easy, we just need to track the motion of the sunspots. This isn't as simple as calculating the changes in relative positions of the sunspots, though, as the Earth is rotating and revolving, which makes the calculations harder. This measurement can be done using the celestial sphere (the field of stars that we see) as a "fixed" reference point and seeing how the Earth and the sunspots move relative to that.

Almost everything in the universe rotates/revolves, at least a little bit, because angular momentum is hard to get rid of. It can be transferred from body to body, but for a body to end up with zero angular momentum, it needs to meet another body with the exact same angular momentum and collide with it in a particular way. Given that this is pretty rare, all celestial bodies rotate.

In addition to that, a non rotating body that is revolving will eventually start spinning due to tidal forces.

• So if the sun were not to rotate, it would start doing so (albeit it seems extremely slowly) thanks to its revolution around the Milky Way?
– VF1
Commented Feb 26, 2017 at 3:27
• Well, it is a bit complicated to answer, because stars in galaxies do not follow expected orbital speed patterns. Mercury (near the Sun) travels at a higher speed, while Uranus (far from the Sun) travels more slowly. On the other hand, stars close to the center of a galaxy travel more slowly, compared to stars further out: universeadventure.org/final_frontier/dkmttr-rotnvelocities.htm . Also, the Sun is part of a local group of stars, within an arm of the Milky Way galaxy: visualcapitalist.com/cp/map-of-the-entire-known-universe Commented Oct 20, 2022 at 9:34
• And since the force of gravity decreases as 1/(radius squared), any tidal force on the Sun from nearby objects will be strongly dependent on the Sun's distance from them. In this case the tidal force is the difference in gravitational force between the front and back of the Sun from another object. Tidal forces are one way to affect an object's rotation on it's axis. This is the main reason we only see one side of the Moon from Earth- the moon is 'tidally locked' to the Earth because the force of gravity from the Earth is stronger on the 'front' of the Moon than the back. Commented Oct 20, 2022 at 9:34
• All of that is to simply say that objects (e.g., stars) close to the Sun will have a far greater effect on the Sun's rotation on its axis than objects far away (e.g., the black hole at the center of the Milky Way. Commented Oct 20, 2022 at 9:36

Yes, the Sun rotates. This can be observed by tracking a variety of features on the Sun, such as sunspots, X-ray brightpoints, coronal holes, filaments, and small magnetic flux elements. Another way to determine the rotational speed of the Sun is to measure spectral lines at the edge of the Sun's disk and determine their redshift.

It is thought that the rotation of the Sun is due to the way the primordial gas cloud collapsed in on itself to create the Sun. Also, it is likely that the Sun originally rotated much faster when it initially formed, than it does to day. This slow-down was probably caused by 'magnetic breaking' in which strong magnetic fields threading our primordial Sun out into the solar wind resisted the rotation.

Today, the reason that the Sun rotates at a different angular speed at different solar latitudes is due to hydromagnetic effects. One cause is thought to be the nature of convection within the outer third of the Sun. Interestingly, below a the convective envelope, beneath a boundary called the tachocline, the Sun rotates as a rigid body. You can find more about this in Schou et al., 1998

• +1 This answer is much more informative than the accepted answer. You pack a lot of clear explanation and physical description into ten tidy sentences!
– uhoh
Commented Nov 13, 2016 at 17:12

Although its too late to reply to this interesting question but trying to add few more points.

Yes the sun rotates.

Now the question arises as to how we can check that?

We can observe this by observing sunspots. All sunspots move across the face of the Sun. This motion is part of the general rotation of the Sun on its axis. Observations also indicate that the Sun does not rotate as a solid body, but it spins differentially. That means that it rotates faster at the equator of the Sun and slower at its poles. (The gas giants Jupiter and Saturn also have differential rotation.) The movements of the sunspots indicate that the Sun rotates once every 27 days at the equator, but only once in 31 days at the poles.

You may refer this interesting article:- Does The Sun Rotate?

• Here is a nice place to watch the daily movement of sunspots: spaceweather.com Commented Aug 4, 2014 at 19:36
• This is an old thread, but I found this interesting. Young suns, when they just form often rotates very fast. Not once every 31 days, but once a day or several times a day. This is similar to the skater who spins faster when he/she pulls in their arms. The conservation of angular momentum can make young stars spin very fast. They slow down over time, probably due to planetary tidal drag Commented Mar 24, 2015 at 5:41
• No they slow down due to coupling between the stellar wind and magnetic field. Commented Oct 16, 2015 at 15:08

Yes, Sun has differential rotation. Movement of Sun spots is one of the proofs that Sun rotates. The differential rotation causes the weird twisted magnetic fields which shows in the Sun's prominence.

Yes the sun rotates and it takes about 26.24 days.They are many methods to determine the rotation periods but most common one is by observing sunspots.

Here's a link with a detailed explanation https://en.wikipedia.org/wiki/Solar_rotation.

So, far all the answers have shed light on the experimental reasons. But you can say it with full confidence without any astronomical observations that the Sun rotates.

The logic is that any closed system have a center of mass that is unaltered unless acted upon by some external force. So, given that Earth rotates around Sun then the system forming Earth and Sun must have a center of mass which is not changing. Therefore Sun must rotate to counter the change in center of mass caused by the rotation of Earth. And so it does with any other system belonging to our solar system.

• The rotation of the Sun wouldn't do anything the counteract Earth's motion. The Sun orbits the center of mass of the Solar System; that's what keeps the center of mass essentially unaltered. Commented Sep 10, 2017 at 1:26