Spots on the Sun


Have you ever looked at the sun, and seen something like this?

Now, before you decide to look at it right now and see what you see, it’s my responsibility as an amateur astronomer to remind you of the safety risks. Focusing your eyes on the sun is dangerous—there’s a reason our eyes automatically flinch away.

How dangerous, you ask? Dangerous enough to burn and even scar your retinas, permanently damaging or even destroying your vision.

Yes, I’m serious.

Now, all this is not to turn you off solar observing entirely. There are safe—and cheap—ways to look at the sun, and see its spots.

But what exactly are sunspots?

Here’s a more up-close and personal view of a sunspot. They’re a bit more complex than they look in a normal image of the sun.


Sunspots are relatively dark regions of the solar surface (photosphere).

But…wait. What do I mean, relatively dark?

Well…here’s a fun fact for you. Imagine that you could take away the sun, but keep the sunspot. It would be brighter than the full moon.

Yes, I’m serious.

Sunspots are about 4200 K (3927℃, 7100℉). In contrast, the photosphere is about 5800 K (5527℃, 9980℉). Sunspots themselves may be extremely bright, but they don’t hold a candle to the brilliance of the photosphere. That’s why they look so dark.

So…how come there are random regions of slight dimness on the solar surface?

There aren’t. Like most things in science, there is a pattern—we just have to look for it. And the astronomer E. Walter Maunder of Greenwich Observatory figured it out.


What you’re looking at here is a graph of the number of sunspots observed each year. Years are on the horizontal axis; sunspot counts are on the vertical axis. And you can see there’s a definite pattern.

If you examine the graph more closely, you’ll find that there are sunspot cycles of eleven years. Early on in the cycle, we see sunspots at higher latitudes on the sun—closer to the poles. Later on, we see them closer to the sun’s equator.

Maunder butterfly diagram.gif

This diagram even has a special name. Want to venture a guess at what it is?

Yup, you guessed it—it’s the Maunder butterfly diagram.

You can see how this graph makes sense. Look at the year 1880, for instance. See how the sunspot data points are plotted at more northern and southern latitudes? But then if you look at the data just before 1890, the data is all plotted very close to the equator.

The butterfly shape is just a coincidence. And again, you can see the 11-year pattern. Every 11 years, we repeat that same cycle of sunspots.

Well…not exactly the same cycle. There are some distinct differences. But I’ll explain that in my next post, when I talk about the sun’s magnetic field.

Wait a second…what about the magnetic field? What does that have to do with anything?

Well, believe it or not, that’s why sunspots form.

sunspots & magnetic field.png

It’s not certain, but scientists believe that sunspots are evidence of the sun’s magnetic field poking up through the photosphere.

Magnetism is as strong as it is mysterious, especially when we’re talking about highly mobile gases. And when magnetic field lines poke up through the photosphere, they trap the sun’s hotter gases below, preventing them from rising all the way up.

What exactly does that mean? If that hot gas can’t make it to the surface, those regions of the surface will appear a bit dimmer. In fact, they’ll appear a bit like…well, a sunspot.

So…how do we even know the sun’s magnetic field is involved? I mean, it’s not like we sprinkled iron filaments on the sun to see what shape they made…did we?

Nope, we didn’t. But we can use what we call the Zeeman effect to our advantage instead.

To understand the Zeeman effect, it’s important to understand a stellar spectrum. I’ve written several posts these in the past, but here’s a quick review.

spectral classification

What do you think you’re seeing here?

It’s true that you’re looking at a rainbow. Very much so. What you might not realize is that each color of the rainbow has a different wavelength—that’s what makes the different colors in the first place.

What do I mean by “wavelength,” you ask? Well, visible light is just one form of radiation, and radiation exists in waves—shaped just like the ones you find in the ocean. The wavelength is the distance between crests of the waves.

You can tell what any object in the universe is made of because its atoms—its materials, essentially—interact with those waves.

Either the materials in the object are only emitting certain wavelengths, in which case the bright lines on the spectrum tell you what’s in the object, and you get an emission spectrum


…or you get an absorption spectrum, in which case the object’s materials are blocking certain wavelengths, and you can tell what materials they are by which wavelengths are blocked (and appear as only a dark line where color would otherwise be).

The Zeeman effect deals with the sun’s spectrum. For reference, here’s how the sun’s spectrum normally looks.

sun's spectrum.jpg

Notice how all these lines are very dark and precise? They don’t get wavy, or split, or do anything remotely unusual…

…unless we take a spectrum of gases that are trapped in the magnetic field.

zeeman effect.jpg

Here’s a spectrum taken of one single sunspot. Notice what happened?

Take a close look at the spectral lines on the right. Are they precise and straightforward? Or are they a little…split? Like they’re plucked strings and we’re seeing triple?

(Seriously, though, doesn’t it look a bit like a plucked string?)

Okay…what is happening here?

Atoms do something funny when they get caught in a magnetic field. Instead of blocking (or emitting) light at specific wavelengths, they get their capabilities expanded a bit. They’re able to create multiple spectral lines where, before, only one existed.

And this is how we can tell that the magnetic field is unusually strong in sunspots. We can then conclude that it’s trapping hot gases below, creating these slightly cooler regions on the sun’s surface.

I’ll bet you’re wondering when I’ll finally get around to sharing my secrets about observing the sun. Don’t worry—I’ve got a few for you.

First: As an amateur astronomer who hangs out with amateur astronomers, I’d be remiss not to mention our cool toys. Below you see a Coronado, a telescope made specifically for viewing the sun.

coronado telescope

If you’ve already got a quality telescope and don’t want to spend money on a Coronado, you can always go for a cheap astronomer-style upgrade and get a solar filter.

telescope solar filter.jpg

The filter is the white ring thingy tacked onto the end that points at the sky. Let me be clear here—if your telescope is NOT specifically a solar telescope, do NOT look at the sun through the eyepiece.

A solar filter can cost between $20 and $70 if you’re going for the cheap range, and it’s a good upgrade for an already-expensive scope.

If, on the other hand, you’re thinking of something that’s more on the cheap side, but still quality…I’d just recommend just buying a cheapie telescope. Seriously. Get the kind you don’t show off at astronomy club meetings. And get a big white sheet of paper.


I’m serious. It works. And it’s cheap. I mean, you’ll get a better image out of a better quality telescope, but if you really want to go cheap, this is the strategy for you. You’ll still be able to see sunspots in all their magnetic glory.

This post has only scraped the surface of the intricacies of the sun’s magnetic field. Next up, we’ll explore it in all its complexity.

63 thoughts on “Spots on the Sun

  1. I just looked at your countdown timer. Neat I like it, I think your site is nicely organised, have you thought about maybe giving it a makeover with other theme to make it really stand out so it would be totally geeky awesome?

    Liked by 1 person

    • Not really…I like the theme I’ve got right now perfectly fine. I’ve actually browsed other themes in a search for more customizing wiggle room but none really work for the blog.


      • I’m actually strongly considering doing self hosting so I have more control over the site and can “mess about.” Trying to learn PHP language so I stand a chance at doing it right.


      • Lol. I am very well versed in HTML now—I figured out a lot of it myself just though working with WP, and CSS makes marginal sense to me, but JavaScript and PHP are currently escaping me. All the while I’m paying $10 a month to own a self-hosted site that I actually don’t know how to program. (It’s like trying to write a book—HTML is kindergarten, PHP is university, and you can write all you want in kindergarten but it’s never gonna look like anything more than a cute attempt.)


      • I wouldn’t know cuz I don’t know python, but PHP is the programming language WP’s software uses. Basically, if you wanna graduate to, you have to know PHP. It uses HTML, CSS, and JavaScript, so it’s basically like those languages are grade school and PHP is university, which builds on them. I’d give you more details, but…like I said, CSS is barely sticking in my brain, let alone JavaScript and PHP.


      • Oh well, I’ll get there…it’s not like I’m in any hurry, I can choose not to renew my hosting account anytime. Maybe I’ll just stop it at the end of the month and then focus on learning coding, without $120 a year to worry about. (I still don’t know why I just up and decided to go for self hosting so soon, it’s money and I don’t know how to code.)


      • Indeed…what I would love is just a blank canvas site to practice coding on. Not a giant big-deal thing with all my posts uploaded from SaYD. Unfortunately, that would actually cost around twice as much—my hosting account gives a 50% off discount for users and it’s the only reason I went for it in a hurry.


      • Meh. For now I’m just sticking to my WP Personal plan. And I’m discontinuing my self hosting after this month. The stupid thing is that SaYD’s budget for this year is entirely gone, but there’s always next year. I figure I’ve got plenty of time to supercharge my web presence…why not stick to the simple things for now, like actually posting content?

        By the way, on the subject of our Star Trek discussion, I don’t suppose you’re at all interested in general-audience fan fiction? (Mine, to be specific.)


      • Content is good, but I think you have lots anyways, why not spend more time promoting it and getting more traffic.

        You have written some fan fiction? Of course I’m interested. ☺️

        Liked by 1 person

      • Well I have this series I’m working on called Trials of Peace. It takes place 900 years after DS9’s conclusion in a time when the galaxy has been swallowed up by the Romulan Empire, the Federation is in retreat, and civilians rely on the rogue renegade Miro Dax to save the day. (He’s Dax host #20 and is by no means a savior, just ends up in the position to play hero more often than not.) Odo, with his incredible Changeling lifespan, is still around, and Kira Eeris, Kira Nerys’s direct descendant, is the primary protagonist. There are currently two stories posted, one pending review, and ten more to go. It’s been a lot of character development exposition so far but it’s going to get epic as the Dominion enters the Alpha Quadrant once more and threatens everything Eeris, Odo, and Miro try to protect. It’s also got a few redemption arcs snuck in there.

        It’s a balancing act, and this blog is less than 9.5% complete. When it has over 100 posts per science field, I’ll consider it an adult blog ready to take on the world, though I certainly won’t stop there—there will always be more posts to come.


      • Archive for fanworks from basically every fandom you can think of. If it’s not there already, any user can add it themselves. I have an account and I post all my stuff there. You’ll find a few other fics but my main project is Trials of Peace.


      • I’m a bit biased, but yes you should 🙂 I don’t have a single dedicated reader besides my beta reader. It would be nice to know someone is reading it for just the enjoyment of it. (And if I’m completely honest, it would be nice to have someone to talk about my characters with—my beta reader is not a particularly conversational person. 😉 )

        Liked by 1 person

      • So I just did some actual calculations. Turns out SaYD is about 2.6% complete. From the looks of that, it’s time to keep rolling out more content.

        By the way, what would you think of SaYD being a more static site? Like, someday in the future when I get the self-hosted thing figured out, what if I didn’t “post” regularly and instead each new article was presented as a page on the site? I’m thinking each science field in the menu would link to a page with links to all articles on that field. I just get the feeling that science sites are more reputable than science blogs, but that could just be my self-doubt talking.


      • You can do that but I don’t see the point. Every post is a page in itself if you organise it. You can then promote it on social media. Making it a post also means your followers get informed of new posts.

        Liked by 1 person

      • Hmm, true…and I can do my page-with-links system with posts, it’s simple HTML, I can just program it to link to all the posts in a category. I mean, that won’t work when I have over 100 posts per category, but it’s workable enough for now. I just don’t know how I’m gonna organize everything when I’ve passed that 100 posts threshold. Archive pages cut off after like 10 posts, so that’s no good…I suppose I just better hope gives me the programming freedom I need or I’ll have to build this site from scratch. And I’m not looking forward to building the commenting, subscribing, and post-updating functions from nothing, that sounds like developer territory.


      • Add categories to break it up? My categories are my science fields, I can’t just assign astronomy posts to, I don’t know, neurology, just to break it up. Hmmm…ok now I’m wondering if there’s a way to organize them by tags as well…I can easily separate out different aspects of, say, astronomy, by the tags that identify individual topics…but is there a way to program my lists that way??? Say, one list of links contains posts from the category “astronomy” but only those with the tag “electromagnetic spectrum”? Ok…I can tell this is gonna test the limits of my HTML savvy…

        Now I’m wondering if there’s some way to program drop-down lists within a page. Because that would be perfect to declutter the link-lists—only let readers see what they choose to see. (If this requires self-hosting, I’m gonna tear my hair out because I can’t afford that for a while yet…)


      • Seriously? I mean, I figured out how to do it with HTML, but I can’t find the menu tool that does that. Is it not in the WP personal plan or am I just terrible at looking for things (and doing things the easy way)?


      • I find it when I’m logged into WP and I look at my page online there’s a little customise icon that appears in the bottom right. I click on that and you get all these customise options for the site including menu’s.

        Liked by 1 person

      • Yeah…I see that too, but nothing about menus. Ohhhhh…you’re talking about the site’s navigation menu? I’m talking about drop-down menus within a page. Check out the link I sent you, you’ll see what I mean 😉


      • Took me forever to get them right! I’m not too bad at HTML but I usually get something wrong…in this case it wasn’t working on the mobile site cuz I had an error in the tags…etc etc. That’s my coding life. Anyway now it’s up and running well, I think…my new post showed up under the right header and all, so I’m assuming that’s a good sign.


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