We can’t see below the surface of the sun.
That makes sense, really. We can’t see below the surface of the Earth, either—we have to get creative if we want to find out what goes on below the crust.
In the sun’s case, we can’t see below its photosphere because the gases within are so dense, light can’t escape. And we depend on light to see anything.
So…if we can’t see inside the sun, how do we study it?
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When we observe our sun’s corona, we discover something odd.
It’s really, really hot.
But…wait a second. How is that odd? Shouldn’t the sun be hot?
Well…yes. It should, and it is. Its surface temperature is almost ten thousand degrees Fahrenheit, and its core is many times hotter. But there’s a basic law of physics that says energy flows from hotter regions to cooler regions.
The core and photosphere (the visible surface) follow this rule. Even the chromosphere, the lower atmosphere, does as it’s told. But the corona is made up of gases that are hotter than the chromosphere.
What’s up with that?
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This diagram is a tiny bit misleading.
Here, it looks like the chromosphere is the visible surface of the sun, with the photosphere just below. Really, we never see the chromosphere. If you ever look through a solar telescope at the sun, the photosphere is the surface that you see.
The sun is structured a lot like the Earth, just in that it has a core, a dense region between the core and the surface, a “surface” layer, and a few atmospheric layers. The chromosphere is part of that solar atmosphere. And you never see it.
Well…almost never.
Continue readingRecognize this?
You might, if you’ve ever seen the sun through a telescope before. What you’re seeing is the photosphere, the layer of the sun whose light reaches Earth. This is the only layer you’ll ever see, without the aid of a solar eclipse.
Wait a second…what do I mean, layers? I mean, I know what a layer is, but what kind of layers does the sun have?
Well, it’s got a few, just like the Earth.
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How hot would you say this star is? Take a wild guess.
Well…sorry, but I’m going to stop you for a moment just to make sure we’re all using Kelvins. The Kelvin scale is like the Celsius scale, except water freezes at 273 K instead of 0℃. 0 K is absolute zero, which is purely theoretical and doesn’t exist.
Now can you guess this star’s temperature?
I’ll give you another hint. This is a real photograph, so it’s impossible for this star to be any star other than our sun. How hot do you think our sun is?
Okay…I’ll tell you. It’s about 5800 K, which—for those of you unfamiliar with Kelvins—is about 5527℃. Kinda crazy, huh?
Next question. How do we know this? I mean, it’s not like we stuck a thermometer in the sun’s surface and actually measured it, right?
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Have you ever been to the beach?
If you’re from California like me, then I’m betting you have. If you’re from a place that’s not near an ocean and you’ve never been near the water all your life, then I’ll tell you a little bit about the tides.
They happen every day, twice a day. If you find yourself a nice comfortable spot overlooking the beach, you can see the waves come into the shore and then gently roll out again. If you stay for hours on end, you’ll see the water level eventually rise a bit.
And if you stay even longer, you’ll see the water level lower back down. When it’s high, it’s called high tide, and when it’s low, it’s called low tide.
The tides are partially responsible for the myth that the moon’s gravity affects you in some kind of metaphysical way. But this isn’t true at all.
So why do the tides happen?
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So, the moon stays in orbit around the Earth, right?
Yeah, I thought so. But why? The moon’s orbit is not a straight line, which means it’s accelerated motion (using the physics definition, which is absolutely any change in speed or direction).
And in order for acceleration to happen, according to Newton’s first law of motion, a force has to happen—meaning, something has to reach out, touch the moon, and drag it into orbit around Earth.
Well, that doesn’t happen, last I checked. I mean, it’s not like we have some kind of giant cord connecting us to the moon. How crazy would that be?
So why does the moon orbit the Earth?
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When you hear the name “Galileo Galilei,” what immediately comes to mind?
If you thought, “inventor of the telescope,” you’re not alone. I also wouldn’t be surprised if you thought “condemned by the Inquisition for believing the Earth orbited the sun.”
But neither of these are true. If you’ve been following my more recent astronomy posts, you probably realize why—in Galileo’s time, people already knew that the Earth moved around the sun.
The idea that he invented the telescope is more understandable…but, again, it’s not true.
So what is true about Galileo, and how did he contribute to our understanding of astronomy?
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Thales and Pythagoras suggested that the natural world could be understood. Aristotle dared to imagine what was beyond the Earth. Plato encouraged thought about the universe, even if he did take astronomy one step forward and two steps backward.
Copernicus followed in Ptolemy’s wake, devising the revolutionary heliocentric (sun-centric) model of the universe. Tycho Brahe may have (incorrectly) rejected that model, but he did make some of the most detailed night sky observations yet.
What’s more, by Johannes Kepler’s time, Tycho had cast doubt on the idea of uniform circular motion that had plagued astronomy for centuries.
At last, the world was ready for a more mathematical take on a question that had confounded philosophers, mathematicians, and classical astronomers alike: how do the planets truly move through space?
By standing on the shoulders of giants, Johannes Kepler was finally able to devise his three laws of planetary motion, which are still the leading mathematical theory today.
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It is surprisingly difficult to find a flattering image of Tycho Brahe.
Honestly. Do me a favor and do a Google image search for the guy. It’ll come up with all sorts of disfigured images, mostly because his nose got messed up in a sword fight…
I know what you’re thinking. A classical astronomer in a sword fight? Suddenly these people seem less like heroes of modern-day science and more like human beings with lives of their own.
Tycho certainly fits the trend. He’s known for being quite the unpopular sort. Bad-tempered and vain, there were few who respected him for more than just his astronomical accomplishments—and even those were few.
So why is he even important, then?
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Science at Your Doorstep 