Why does the sun rotate faster at its equator?

Question

I just tell my students that because the sun is fluid, it spins at different speeds. I'm always hoping they don't ask for the physical explaniation.

Thanks for all of you that attempted to answer my question. Unfortunately, I'm not getting the answer that I was looking for. I'll keep searching!

In response to zee-prime...
Your answer seemed most promising, but isn't Hadley cells on earth caused by differential heating on earth's surface (sun heats near the equator more than the poles)? On the sun, the convection occurs but not as cells like on earth.

Answer 1

The outer part of the Earth, the atmosphere, is a gas, and at different latitudes there are different wind belts. Near the poles, there are polar easterlies (meaning they blow from east to west). The Earth rotates from west to east. At temperate latitudes you've got westerly winds. In the tropics is the trade wind belt, where the winds are easterly. So as you go from pole to equator, first you run into winds which carry air around slower than the Earth's solid surface, then faster, then slower again. The reason the Earth's atmosphere rotates at different speeds is because in each hemisphere are three convection cells, Hadley Cells, caused by hot air rising at the equator and cool air sinking at the poles. If the Earth didn't rotate, you'd just get rising and falling motion, like convection currents in a room, but the Earth's rotation deflects these air currents to give our familiar wind systems. The Sun's meteorology is very different from Earth's but like Earth the Sun is spinning and like Earth it's got convection currents, but they're caused by hot gas rising from the interior where nuclear reactions generate the heat. Like Earth, the Coriolis force produced by the Sun's rotation deflects rising and falling gas into zonal (sideways) wind systems. On average it takes a constant level weather balloon 23 hours 56 minutes to make one trip round the Earth's axis, but near the pole and near the equator it takes a bit longer, and in the mid-latitude westerlies, it takes a shorter time. Similarly, on average it takes the Sun about 25 days to spin once, but the exact time depends on your latitude.

Answer 2

The wording is a little wonky, but it's true, a point on the equator of a sphere will travel faster than a point that is radially closer to the axis.

The math escapes me, but you can explain this rather intuitively. Draw a big circle on a piece of paper. This represents the path of a point on the equator. Now draw a smaller circle inside that, which represents a non-equator path.

In one rotation, an equal number of radians are traversed per unit time. However, the point on the equator travels more distance, since the circumference of that path is larger. More distance travelled in the same amount of time = faster.

by the way, this is true for any spherical body, not just the sun.

Answer 3

Try a human chain experiment...

Start off with one student spinning at a constant rate in one position (this movement can be slow). Then, while maintaining the initial rate of spin, add another student and then another... The students should be joined hand in hand forming a longer chain with the original student at the center (pivot) position...

By doing this experiment, your students will learn by example that as you increase your (perpendicular) distance from an objects rotational axis the objects at greater distances from this axis maintain a "faster" spin velocity for the same rotational rate.

The reason why the sun moves faster at its equator is because the equator is the furthest perpendicular distance from the sun's rotational axis.

That's what I first visualized after reading your question, I hope this helps...

Answer 4

Different areas of the sun rotate at different speeds because the sun is a gas, not a solid, but I forgot the reason for it. Maybe it has something to do with the law of the conservation of angular momentum.

Answer 5

If you cut the sun in flat circles, the equator would have the largest circumference. With every circle completing one rotation at the same amount of time, the equator travels farthest with the same amount of time.

Answer 6

I think the answer is because of the amt. of space that must
be traveled to reach the same destination at the same time.
If you think of the globe as having runners standing abreast,
the one standing at the equator has twice the distance to
travel as the one at the poles. He must run twice as fast.
Can you picture that? Does it make any sense?