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One of my favorite objects to show people at astronomy outreach events is the Orion Nebula. Not only does it reside within a fairly well-known constellation, but it’s a gorgeous sight to see with a good telescope.
There’s no time like the present up here in the northern hemisphere. Orion is a winter constellation and rises high in the sky this time of year. Not to mention, as a stellar nursery, talking about the Orion Nebula follows on perfectly from my last couple posts on star formation.
If you’ve ever seen the Orion Nebula through a small telescope, you’re probably wondering what all the rage is about. It mostly just looks like a bluish haze around a star—like the telescope operator didn’t tune the focus quite right.
But if that’s all you’ve seen, I promise you, you’re missing out…
If you’ve had the opportunity to observe the night sky from a dark place, far away from the light pollution of the city, on a clear night, you might have seen this before. It’s the Milky Way—our view of our galaxy from the inside.
It’s kind of like if you lived inside a frisbee. Look up toward the flat sides, and there’s not as much material to look through. But peer out at the edges of the disk, and you have to look through a lot more stars.
Most of the stars you see in the night sky are part of the Milky Way. But this is the sight we get when we stare through to the center of the frisbee.
Thing is, though, this is far from the most spectacular sight of the night sky.
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?
Find yourself a dark, unpolluted night sky on a clear night free of clouds, and you are very likely to look up into the heavens and see a sight quite like this. It’s what we see of the Milky Way, our galaxy.
When I’m at an astronomy event with a sky like the one above, I find it absolutely incredible. Do you notice how the stars don’t all look the same?
A couple are startlingly bright, there are numerous stars that are somewhat dimmer, and if you look really hard, you notice that even the dark night background is sprinkled with stars so faint they can barely be seen.
But what if I told you that you’re not even seeing the half of it?
You probably recognize this image. You see something like it whenever you look up at the sky. Some days are clearer than others—some, you might even see a completely blue sky—but regardless, you know that this is an image of our atmosphere.
But do you know just how much your atmosphere does for you?
We’ll talk about how it protects you from space rocks later on. For now, consider the energy from our own sun. The sun doesn’t just send visible light our way—it operates in all wavelengths of the electromagnetic spectrum.
Some of those wavelengths are harmful, like gamma rays, X-rays, and ultraviolet radiation. Others, like infrared radiation, microwaves, and radio waves, are perfectly fine.
The atmosphere doesn’t really pick and choose which wavelengths get through to the surface. It blocks out some radiation it doesn’t need to. At least it protects us from the harmful wavelengths.
But that’s bad news for astronomers, because those wavelengths still contain useful information about the universe.
Okay, maybe you have…online. What with the spread of the internet these days, I’m guessing that at one point you have seen something like this on a page of image search results.
That’s the thing, though. You’ve seen this incredible phenomenon on a computer screen. But have you ever seen it through a telescope?
Don’t worry—if you haven’t had an opportunity to look through a telescope, you’re not missing out. You’re not going to see the Sombrero Galaxy above in all its photographed glory just from looking through the eyepiece of a telescope.