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Down here, on Earth, if you look up at the night sky, it seems like all the stars up there look the same. Or maybe at least similar. But, it turns out that stars are very different and we shouldn't stereotype them. Some are bigger, some burn through their hydrogen faster, some are one color, and some are another color. In this episode of Crash Course Kids, Sabrina chats about their difference and tells us what those differences mean.

///Standards Used in This Video///
5-ESS2-1. Develop a model using an example to describe ways the geosphere, biosphere, hydrosphere, and/or atmosphere interact. [Clarification Statement: Examples could include the influence of the ocean on ecosystems, landform shape, and climate; the influence of the atmosphere on landforms and ecosystems through weather and climate; and the influence of mountain ranges on winds and clouds in the atmosphere. The geosphere, hydrosphere, atmosphere, and biosphere are each a system.] [Assessment Boundary: Assessment is limited to the interactions of two systems at a time.]

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Producer & Editor: Nicholas Jenkins
Cinematographer & Director: Michael Aranda
Host: Sabrina Cruz
Script Supervisor: Mickie Halpern
Writer: Alyson Shaw

Executive Producers: John & Hank Green
Consultant: Shelby Alinsky
Script Editor: Blake de Pastino

Thought Cafe Team:
Stephanie Bailis
Cody Brown
Suzanna Brusikiewicz
Jonathan Corbiere
Nick Counter
Kelsey Heinrichs
Jack Kenedy
Corey MacDonald
Tyler Sammy
Nikkie Stinchcombe
James Tuer
Adam Winnik


Sabrina: My brain still hurts from last time. It's like intergalactic whiplash. You too?

But there's a reason we zoom through the mega giant unbelievably huge vastness of space. It helps us understand how big the universe really is, not just how big it appears from our perspective down here on our itty bitty Earth.

If you glance up at the night sky, the stars seem like they're all on the same planes, that is at the same distance from Earth, and the stars all seem pretty similar, but don't let your eyes fool you. Some stars are relatively close, just four or so light-years away, and some are hundreds of thousands of light-years away.

The furthest stars are billions of light-years away. BILLIONS, people! And in the big, huge spacey-ness of space, there's a lot of room for variety. Even in our galaxy, the Milky Way, there's a wide range of stars, so stop stereotyping them. Let's take a look. What are the different kinds of stars?

(Big Question)

Well, scientists organize stars by their color and size. Which also happens to be how I organize my rock collection. We've learned that stars glow because they create energy through nuclear fusion, but not all stars produce the same amount of energy, and stars can produce different amounts of energy throughout their lifetimes.

I mean, they're not alive, but in a sense stars are born, grown up, age, and eventually die once they burn through all of the hydrogen in their core. And don't feel bad, this happens over billions and billions of years.

Now, first thing to remember, stars that produce less energy glow red. These stars are relatively cool with a surface of about 2,760 degrees Celsius, but the very hottest stars in the universe glow blue-white. Put on your shades because these stars can have a surface temperature of over 30,000 degrees Celsius. Our sun, by the way, is a perfect mellow yellow temperature, right in the middle with a surface temperature around 10,000 degrees.

Stars also come in a range of sizes. The smallest known star is just a little bit bigger than Jupiter. Pretty small considering you could fit about a thousand Jupiters inside our sun. Meanwhile, the largest star that we know of is many hundreds of times larger that the sun. If it were in our solar system, it would extend past Saturn's orbit! Once again, our sun is in the middle of this range. We're in a real life Goldilocks situation, here.

So now that we know how stars are classified, let's see if we can identify two of our star neighbors. I've got the perfect stars in mind, a foot and an armpit. Oh, have you met Orion?


He's one of the most recognizable constellations, and he's got two body parts that are made from totally different kinds of stars. Remember Betelgeuse? We talked about this star in a previous episode. It's the right shoulder, some people like me call it the armpit, of Orion. And let me introduce you to Rigel, Orion's left foot.

Betelgeuse and Rigel are both in our home galaxy, the Milky Way. Take a look at this picture of Orion. Based on the evidence that you can see, which would you argue is hotter? Does one star look kind of reddish and another kind of blue? You smarty-pants, I bet you already guessed the answer.

Betelgeuse, the armpit star is a red supergiant. It's much, much cooler than Rigel and sadly it's nearing the end of its starry life. ON the other hand.... er, foot, Rigel is a blue-white supergiant star. This star is in the prime of its life, burning super hot and super bright. But stick around a few million years and Rigel will probably start to look like Betelgeuse, red and cool.

Now, since Rigel shines more brightly, you might assume that it's closer to us, and that would be a great guess, but using brightness to judge distance can be tricky. Rigel has much greater true brightness, or luminosity, than Betelgeuse, so the foot outshines the armpit.


So in summary, a star isn't just a star. From here on Earth the stars may look similar, but you know better now. They come in different colors and different sizes; you could say they're got their own personalities. Stars: they're just like us. Except millions or billions of miles away. And gigantic. They're not really like us.