Where Did the Interstellar Medium Come From?

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Contrary to popular belief, space is not empty. The space between the stars is filled with clouds of dust and gas. And this space—the interstellar medium—is incredibly beautiful and fascinating.

I often refer to the interstellar medium as the galaxy’s “backstage.” Why? Because it’s not the part of the universe that astronomy enthusiasts usually think about. And yet, there are whole studies devoted to studying this natural wonder of the universe.

Also, the interstellar medium is largely hidden from us. There are ways we can detect it—when light from a distant star passes through it, for example. And with our eyes, we can see nebulae, the visible evidence of this interstellar expanse.

The backstage of a theater is similar—it’s not the main part of the show, but you sometimes see evidence of it in the forms of new costumes donned as the play progresses and new props brought into play. The audience often forgets about it entirely.

Nevertheless, it’s beautiful. Stars are born out of giant molecular clouds, triggered by compression from expanding bubbles of coronal gas. The interstellar medium spells our beginning.

But how did it get there? Continue reading

The Average Star

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What the heck is the average star like?

We’ve talked about a lot of stars over the past few weeks. We’ve discovered the vast distances between the stars, looked more closely at what really makes a star bright, and covered all kinds of ways to classify stars—from their spectral type to their luminosity class.

Most importantly, we’ve looked at the H-R diagram, the diagram that classifies stars by their color, temperature, composition, and luminosity…and relates those properties with many other features stars have.

We know what kinds of stars are out there. We know they range from thousands of times smaller than the sun to thousands of times larger. We know they range from desperately faint to incredibly luminous. We know they come in all the colors of the rainbow.

But how many blue stars are there? How many small stars are there? Are most of them small, or are there about the same number of small stars as large ones? Continue reading

Just How Big Are Stars?

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Tell me about the stars you see in this image.

They look like billions of little pinpricks of light, right? It’s hard to imagine that each one of these is probably the size of the sun…or much larger. And the sun, by the way, is about 109 times Earth’s diameter.

So if you thought those stars were small…not so.

It makes sense that they would be very large. Their light reaches us from many light years away, with the nearest star 4.3 light years away and the most distant one likely trillions.

In order to radiate that far out and stay bright enough to speckle the night, they would have to be very luminous, and that means having a large surface area, even if they’re not particularly hot.

So how do we know how big the stars are? Continue reading

The True Brightness of Stars

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Have you ever looked up at the night sky and noticed that while relatively bright stars outline the constellations, there are numerous other stars that are almost too faint to see with the naked eye?

If you ever noticed this, you probably guessed that the brighter stars are literally brighter, and the fainter stars truly are fainter. Or maybe you guessed that they don’t vary in brightness that much, but fainter stars are much farther away.

But that’s not really true…or, at least, it’s not the whole answer.

So what’s the real reason why some stars appear to be brighter than others—and how can we tell how bright they really are? Continue reading

Mapping the Sky

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I need you guys to help me with something.

Can you find a horse in this image of the night sky?

Yeah, me neither. I’m lost. I see the Great Square of Pegasus because I know what to look for, but I still don’t see a horse.

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Okay, so now I see half a horse. Where’s the rest?

Your guess is as good as mine, guys. Truth is, constellations very rarely look like what they’re named after. Constellations are more like relics of our ancient past than actual descriptors of what we see up there in the sky. But they do serve a purpose, even if that horse up there is missing his back legs.

I really find myself wondering if whoever made up Pegasus was concerned with animal rights… No animals were harmed in the making of this sky map…

Okay, yeah, never mind.

Where was I? Ah, that’s right. The purpose of the constellations, and the reason why it really doesn’t matter if they don’t look like their names say they do. Continue reading