Interstellar Spectra

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I often refer to what we call the interstellar medium as the galaxy’s “backstage,” and I do that for a reason: for the most part, we can’t see it.

The backstage of any theater isn’t part of the show. You, as part of the audience, never see it. But you see evidence of it, when new props appear as the play progresses through scene after scene and the actors interact with their backstage.

The same thing happens with the interstellar medium. It’s not the hidden area behind the stars of the galaxy. (Ha, get it? Stars?) In fact, more often than not it’s actually the one hiding stars from view. But we can’t see it…unless we study how stars interact with it.

One way to do that is to look at reflection nebulae—evidence of the light from bright young stars reflecting off the dust of the nebula. That qualifies as interaction.

And in the case of emission nebulae, hot O-type stars ionize the hydrogen gas of the nebula. I’d say that’s interaction, too.

Even dark nebulae can technically be seen, since we see them as shadowy clouds silhouetted against background nebulae or stars.

But sometimes, it’s not that simple. Sometimes, we have to rely on the galaxy’s props to guess at what must be stored backstage. And that means studying stellar spectra. Continue reading

Extinction and Reddening of Starlight

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Take a wild guess: What do you think this image is showing you?

If you said it looks like a giant black hole in space, I don’t blame you. I also don’t blame you if you thought it looks like a giant outer space blob…and the funny thing is, that’s actually closer to the truth.

This isn’t a hole in space. We can’t see any stars in this region, but not because there aren’t any. In fact, there are just as many there as there are flanking the giant space blob.

What you’re seeing is evidence of the vast interstellar medium, the galaxy’s backstage. The interstellar medium is the stuff between the stars, often invisible since it’s not hot enough to produce its own light.

Sometimes we can see it as a pale blue reflection nebula, or a bright pink emission nebula. But in this case, we’re looking at a dark nebula—visible only because it blocks the light from stars beyond it. It appears to be a hole in space.

It’s closer to being an outer space blob. But what exactly is it? Continue reading

New: Mailing List!

Hi everyone,

So…I didn’t manage to get posts out this week. Sorry about that. I’m working up to 9 posts a week by August 1st, and according to my calendar, I am on track. I promise, you’ll get plenty of posts next week.

Wait a second…what was that about 9 posts a week?

My goal is to publish 9 posts a week for the next 5 years, starting by August 1st this year.

Many of you may prefer to follow me through the WordPress reader. If you’re alright getting 9 notifications from me in your feed every week, then we don’t have a problem. But if that’s too frequent for you, or if you’re subscribed to this blog via email…I have a second option for you.

I have a mailing list now!

If you join the mailing list, rather than follow me via the WordPress reader, you’ll get one email from me a week, containing excerpts and links to the previous week’s posts. Just pop your email in the “Follow Blog via Email” form in the sidebar and hit “Follow.”

Right now, it doesn’t really matter if you follow me via WordPress or the mailing list. But as a side project, I’m building up a website that’s identical to this blog in every way that matters to you…except it’ll be self-hosted.

When I make the switch sometime in the near future, you won’t be able to follow me via WordPress anymore, but the mailing list will remain.

Don’t worry about that yet. It’s a long way off. But if you’re debating about whether to follow me via WordPress or via the mailing list, I would go for the mailing list. It’s the more dependable option.

Anyway, I look forward to sending out my next science post on Monday! (And there’s plenty more to come after that!)

~Emma

The Stuff of Nebulae

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What you see here is the Trifid Nebula, a vast cloud of gas and dust in space.

In my last post, we explored why it looks the way it does. We discovered that the pink hues of emission nebulae are caused when extremely hot nearby stars “excite” the gas of the nebula itself to emit its own light, which our eyes perceive as pink.

The haze of blue to the right, on the other hand, is the result of light from hot young stars nearby getting scattered among the nebula’s dust particles. It looks blue for the same reason the sky looks blue. We call nebulae like this reflection nebulae.

And the black wisps of dark nebulae are hardly as ominous as they look; they’re simply ordinary clouds of gas and dust, ordinary nebulae, that we can only see because they’re silhouetted by brighter objects in the background.

But nebulae, for all their different names, are actually a heck of a lot more similar than you might think. Continue reading

What is a Nebula?

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What’s a nebula?

Well…you’re looking at one.

Okay, okay, I know. You want to know what that actually is. You want to know why it’s there. You want to know why there are colors in space…and why you’ve never noticed such a thing in your own night sky before.

Nebulae are the stuff between the stars. They’re the galaxy’s backstage. They’re the only visible evidence of a vast expanse of gas and dust between the stars, completely invisible to the human eye, called the interstellar medium.

Nebulae are the sites of star birth. Planets form from the dusty particles present in these glowing space clouds. They’re the galaxy’s way of replenishing itself. And they’re pretty cool to look at, too.

But how come they look the way they do? Continue reading

Star Mass and Density

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What makes a star shine bright?

Much earlier on—probably months ago now—I explained how something called the proton-proton chain generates massive amounts of energy within stars, and enables them to fuel whole solar systems. That’s the battery of a star.

We’ll address the proton-proton chain later, when we start talking about star life cycles. We’ve still got some talk about nebulas and interstellar space to go before we get that far. For now, what’s important is that the proton-proton chain depends on high density.

That is, stars will have the strongest batteries if they have very dense interiors. It doesn’t really matter how dense their middles and atmospheres are. But conditions in their cores must be very dense.

You’ll find, if you study stars closely, that there is a definite relation between their densities, masses, and luminosities. 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

Eclipsing Binary Stars

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Imagine a frisbee.

At the center of this frisbee lies the sun—our sun, for simplicity’s sake. And sprinkled around the surface of its disk are all nine…excuse me, eight…planets of the solar system, plus the dwarf planets, asteroids, moons, Kuiper belt objects, Oort Cloud objects, comets, cosmic dust…

Okay, I could go on, but I’ll stop there. You get the picture. The whole solar system is on this frisbee. It’s a flat plane, disk-like. There aren’t orbits that put the planets up in the air  above or below the frisbee. They all lie, more or less, in the same basic plane.

Wait a second though…isn’t this post supposed to be about eclipsing binary stars? What the heck does our frisbee-like solar system have to do with that?

A lot, actually. Continue reading

Science Questions, Anybody? (#2)

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Most of the time, when I publish posts on this blog, I choose a topic and write about it in the hopes that you’re curious about it. But I also want to know what you are curious about—always.

I want to call your attention to the “Got Questions?” link up in the menu.

This link will take you to a page that invites you to submit a question. Anything about science, anything you’re curious about, just type it out and hit “Submit!” My door is always open, so to speak—that page will always be available.

I’ll still send out posts like this one asking for your questions. But I want you to know that you never have to wait to ask a question. Science is all about being inquisitive, and you should never have to wait for me to prompt you. But you can, if you want 😉

Anyway, this is another “Science Questions” post—you’re welcome to ask whatever you want in the comments below. I’ll address your questions in the order they’re submitted and let you know when the post is published.

And please, by all means head over to my “Got Questions?” page. I want to know what you’re curious about. I want to answer your questions. Most of all, I want this blog to be a place where you feel free to wonder. A curious mind is a healthy thing!

Remember, everyone—there are no stupid questions, only stupid answers. I promise to answer anything you ask to the best of my ability.

Questions, anyone?

Spectroscopic Binary Stars

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Consider a solar system far different from our own. A solar system governed by two suns, and consisting of planets we can only dream of.

Would it surprise you to hear that, based on recent discoveries, that might actually be the norm?

The surroundings we grow up in determine our outlook on the world, and this is never more true than with our solar system. Our eight planets (though some would vehemently insist upon nine) and their parent star are all we know.

But what if I told you that most of the stars you see when you look up at the night sky have companions? And often, these companions are impossible to detect by visual means.

So how do we know they exist? Continue reading