What if I told you that this was an actual image of the night sky?
Well…alright, I admit it’s more like a map.
Specifically, a map of the cosmic microwave background radiation, often known simply as the CMB.
This is the farthest we can see in the universe, and consequently, the farthest we can peer back in time. And it’s a critical springboard to answering some of the most fundamental questions about the universe.
But what the heck is the CMB?
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In my article, “Where Are We?” I showed you just how huge astronomical distances really are. There’s a reason people say that incredible things are “astronomical!”
The image above illustrates how far Earth is from several faraway objects, including one of our nearest neighbor stars, Alpha Centauri.
But what does it mean for two objects to be 4.3 light years apart?
The light year is a unit of distance, used to measure distances that escape traditional units on Earth. It’s impossible to measure the universe in kilometers or miles; many thousands fit into one planet alone.
Even “astronomical units,” the distance between the Earth and the sun, are too small. That distance, as we saw in my last post, is barely a fraction of the distances in our solar system alone.
So, what exactly is a light-year?
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Have you heard of the Big Bang?
I still remember the first time I heard about it. I was little; I can’t remember if I’d fallen in love with astronomy yet. But I do remember sitting in my living room, surrounded by my dad’s scientific journals and magazines.
One cover page caught my eye. There was a full-page illustration of a young student standing before an old-fashioned blackboard, writing over and over, “I believe in the Big Bang.”
I had no idea back then what this “Big Bang” was.
And as it turns out, it’s not what most people think…
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Cosmology is the study of the universe itself: how it came to be, how it has behaved since, and why the laws of physics operate the way they do.
It’s one of the strangest branches of science—second only, I think, to the wacky world of quantum mechanics.
But it’s also fun.
The ideas cosmology proposes can be absolutely mind-bending—and mind-blowing. I find it inspiring. To think that our tiny species—barely ants compared to the broad stretch of deep space, barely a blip in the long stretch of time—can probe this far into the secrets of the universe.
So let’s take the plunge, shall we?
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Active galaxies are, without a doubt, absolutely spectacular.
Though rare, they tell a critical part of the story of galaxies–and of the universe as a whole. And we’ve spent the last few posts exploring them in depth.
But I know they can also be a bit perplexing. These are some of the most powerful and violent objects in the universe; it comes with the territory!
So, let’s boil this down to the basics and tie it all together. And let’s try not to get caught in a supermassive black hole in the process 😉
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Over the course of the last few posts, we’ve explored different types of active galactic nuclei: Seyfert galaxies, double-lobed radio sources, and quasars.
At the heart of each of these galaxies lies a supermassive black hole, feeding off an energy feast of infalling material and producing titanic eruptions of energy.
Most galaxies, though, are not active. The majority of supermassive black holes–like the one sleeping at the heart of our own galaxy–are on “starvation diets,” living off minuscule streams of dust from cannibalized satellite galaxies.
We know what causes these supermassive black holes to erupt. But why are they so rare? What part do they play in galactic evolution?
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Astronomers know that when galaxies’ nuclei become active–releasing tremendous floods of energy–supermassive black holes are the ultimate culprit.
We also know that supermassive black holes lurk at the hearts of most large galaxies.
But most galaxies are not active; only a small percentage are. Our home galaxy is host to a supermassive black hole, but it’s not active. Neither is the black hole within the nucleus of our nearest galactic neighbor, Andromeda.
So, what makes a supermassive black hole erupt?
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We first took a peek at supermassive black holes back in our discussion of galaxies. But now that we’ve covered a few types of active galaxies, it’s time to take a deeper dive.
Okay, I guess we won’t really be diving into a black hole…sorry to disappoint!
(Honestly, though, you really wouldn’t want to. It would be very uncomfortable, to say the least…and, of course, it’s a one-way trip.)
Supermassive holes are thought to lie at the hearts of most galaxies, including our own. They seem to be key to galactic structure. Most of them–including our own–are quiet. But a few percent of the galaxies in the universe emit titanic amounts of energy from their nuclei, and supermassive black holes are the ultimate culprit.
But how?
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Did you know that a total solar eclipse is coming up on April 8, 2024?
This one is primarily visible from North America; you can find more information about where to see it (and if it’ll be visible from your location) over here on TimeAndDate.com.
I was planning to travel to “totality” myself, but those plans fell through because I couldn’t get the time off work. Nevertheless, I’ll be helping out at a viewing event up north of Joshua Tree National Park!
In this post, I’ll take you through what you’ll see during a total solar eclipse–and, at each phase, I’ll let you know exactly how to safely view the sun!
(Later this week, we’ll be back to our regularly scheduled programming on active galaxies.)
Important: Always use solar glasses and solar filters that conform to the safety standard ISO 12312-2. Be careful! There are bad actors on the market that print this standard on unsafe equipment. Use this list of trustworthy suppliers from the American Astronomical Society.
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This post has been updated and republished from Sept 2017.
A solar eclipse is the most amazing astronomical sight you’ll ever see.
Not only is it the only time you’ll ever be able to clearly see the “new moon” phase of the moon, it’s the only time you’ll ever see the sun’s corona. And it’s the only time that, under very specific circumstances, you can actually look directly at the sun for a few moments.
But it’s not just an astronomical event. It’s an experience. You can see the moon’s shadow rushing toward you. Nature falls silent. It’s night during the day.
And there’s one coming up on April 8, 2024.
So, let me tell you a bit about what’s happening in the sky—and give you a few important safety warnings!
(If you’re wondering what happened to our unit on active galaxies, not to worry–I’m still publishing the next post this week!)
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Cosmos at Your Doorstep 