How do they know it takes our sun (about) 27 days to rotate once on its axis? Yes, I hear they observe sunspots. But, is that 100% solid logic?
a) Sunspots come and go. How do you know you what you’re really following?
b) Sunspots go around the back of the sun. Are you certain they are in the exact configuration relative to a stationary point on the sun’s surface? And, surely the sun’s surface is not solid, so is there a stationary point to measure from?
Well, I’ll take the point that what they’ve determined is that whatever layer of the sun shows sunspots rotates in 27 days or so.
But we’re no longer limited to observing the sun from just one vantage point. We’ve launched a number of probes to get closer to the sun and watch it from different orbits, and I’m sure that tracking the rotation of the sunspots was something that they’d do with those.
I’m not sure what the bit about stationary points is in reference to. But as you track sunspots, you can see how much they’re drifting about relative to each other, (as I’m certain they do,) and probably take an averaging over all of them over time to figure out that rotation period. I’d call that at least 99.9% solid logic. (As most of the best science is, perhaps.)
They know because sunspots are very long-lasting. They are specific shapes at specific latitudes. It would be one hell of a coincidence if every single sunspot visible at one time vanished and was replaced by an identical sunspot at the identical location in a variable amount of time yet all turned up together every 27 days. And even more of a coincidence if all the sunspots visible throughout all history behaved magically like this.
The rotation of the sun was settled long ago. These day we have multiple instruments that can read multiple frequencies. They all back up one another. This question is as silly as asking if its the same moon we see overhead every night or whether somebody comes along and switches it out for a different identical moon just the funsies.
As the Wikipedia link says, 27 days (actually 27.2753 days) is the average rotation period of sunspot groups. Yes, some sunspots and sunspot groups disappear or reappear while it’s on the other side, but often they survive long enough to be seen again. Also, you don’t have to see a sunspot go all the way around to measure its speed, you can just measure how long it take to move a certain distance across the face of the Sun.
Of course, the Sun is fluid, so it doesn’t rotate as a rigid body. Different parts of it (different latitude & different depth) rotate at different speeds.
It is a question that’s answered comprehensively with a moment’s googling, but it seems rude to reply with “duh, why don’t you just google it”. Still, while I do know something about astronomy, I’m not going to spend 10 minutes paraphrasing wikipedia. The sensible approach in this situation seems to be to guide the OP toward wikipedia and other online accounts that answer the question, then OP can come back and ask about anything that still doesn’t make sense.
Good grief, isn’t this place-- notably GQ-- about asking questions and fighting ignorance? You answering with “Seriously?” and “this question is as silly as…” isn’t helping anyone. You want to mock someone for asking a question cuz you’re so gosh darned smart? Maybe keep it to yourself.
I mean if the answer to everything is “Google [or Wikipedia] is your friend,” why not just shut down GQ and we can stick with making fun of Trump and listing our favorite Beatles songs.
Allow me to say thanks for asking the question, and thanks to those that actually answered it.
I honestly did not realize that sunspots were effectively static objects. I thought they were ephemeral, coming and going fairly quickly. Ignorance fought.
Keep in mind you don’t actually have to watch a particular sunspot make a complete circuit in order to know how fast the sun is rotating. The sun is rotating at a pretty constant speed. So if you track the movement of a sun spot for a few days, you can figure out how fast the sun is rotating.
Perhaps “layers” wasn’t the best term to use, but the fact is that the sun revolves at different rates depending on what latitude you’re at, with the area near the equator revolving faster than the areas near the poles (25 days vs. 34 days, respectively).
Sunspots are the most visible features on the Sun, so that’s what scientists have traditionally used to measure rotation. Even that depends on latitude, but sunspots near the equator rotate in about 27 days.
But sunspots aren’t flat patches floating on the Sun’s “surface” (photosphere). They are actually cross-section of huge magnetic field structures that are rooted deeper down, and extend far up. These structures don’t necessarily move with the plasma at the photosphere. If you actually measure the flow of plasma at the photosphere, e.g. by measuring its Doppler shift, you find that that layer rotates faster than the sunspots.
Yes, it’s solid logic. But bear in mind that that rotation of 27 days is a somewhat arbitrary average, since the equator rotates faster than the poles.
We can follow them across the surface and have observatories that put together follow the sun constantly. We also know a lot about the inner workings of the sun and can say with confidence that they are moving along with the rest of the upper layers, not drifting significantly faster like a cloud in Earth’s atmosphere moving relative to the solid surface.
We’ve had eyes at the back of the sun for several years with the Stereo satellites, allowing us to see that there’s sudden replacement of sunspots there that we haven’t observed from Earth.
Sunspots are a part of the sun’s “surface”, and there is no stationary point to measure from. Deeper down the gas rotates faster, with the core rotating once a week, but it’s a ball of gas, so the surface that we see is the part it makes sense to talk about when we just ask about the sun rotating.
Years and years of observation and scientific analysis of the observational data.
Also, helioseismology can now generate far side images of the Sun. That’s a worldwide network of telescopes that observe tiny oscillations (sound waves) on the Sun. These instruments, along with lots of computer processing, can “see” the far side of the Sun by measuring sound waves that travel around the Sun.
p.s. for reference, here’s the STEREO web site.
I mocked the OP for poisoning the well. Asking the plain question “How is the sun’s rotation measured?” would get a straight answer with no snark. The OP chose to frame the question in a way similar to the way Creationists or birthers ask questions. There’s no place in GQ for questions that start with the premise that all scientists are idiots. That can be argued in several other forums.
You also might notice that I answered the question properly in any case.
