Why Is Snot Green? - Softcover

  Lost in Space
The universe can be a pretty dizzying place.It was born in an almighty explosion of energy. It’s so massively, hugely, immensely enormous that it’s almost impossible to imagine how big it really is. Within it, there are spinning planets, burning suns, icy comets, and vast clouds of floating dust and rock. Planets, moons, and asteroids whip around each other like cosmic dance partners. Stars are born, stars die, and stars collapse into mysterious black holes in space.But why did it turn out that way?Where is it all headed?Are we all alone in it?And come on—how big could it really be?Want to find out? Then read on ...
How big is the universe?

Big. Really big. Crazy big. Billions of times bigger than the biggest thing you can imagine.
I don’t know about that—I can imagine some pretty big stuff ...OK, let’s give it a shot. Let’s imagine the size of the universe. It’s probably best to start small and work up—so let’s start with something fairly big—the Earth. The Earth is about 8,000 miles wide. If you drove a tunneling car straight through the middle,1 you’d get to the other side in about 5½ days, going nonstop at an average highway speed of 60 mph.

That doesn’t sound so far.Right—it’s not. So let’s try a longer journey. Say, from here to the Moon. The Moon doesn’t go around us in perfect circles—it gets closer and farther away from us at different times of the month. But, on average, it’s about 240,000 miles away. It would take about 168 days to get there in a 60-mph flying space car. Even with rocket propulsion, the Apollo astronauts took about three days to get there (and it was really crowded in their spacecraft).Similarly, the journey from Earth to the Sun is about 93 million miles, so it would take about 176 years by space car. To get right across our galaxy, the Milky Way, it would take about a million billion years (or 1,181,401,000,000,000 years to be more precise) to make the journey of 621 million billion (or 621,000,000,000,000,000) miles.So what does that tell us?

That a space car would be cool, but at 60 mph it’d be pretty useless for getting around in space?Errr ... yes.That, and that the galaxy is pretty huge in itself—let alone the universe. I’m running out of space to put all the zeros after the numbers here.

All right—what if you had a space car that could go at the speed of light?Now we’re talking. The speed of light is about 670 million mph, so a car that fast could go about 6 thousand billion miles (or whole year. We call this distance a light-year, and it’s much more useful for measuring the huge distances—between stars and across galaxies—that we’ve been talking about. For example, the Milky Way is about 100,000 light-years across, so it’d take 100,000 years for our souped-up, super-fast, light-speed car to cross it. Still way too long to manage, but easier to imagine, maybe.

Go on, then—how big is the whole universe?Well, we can only measure the universe as far as we can see it. With the best telescopes we have, that’s about 15 billion light-years (or 90 billion trillion miles—I won’t even bother trying to write that out with zeros) in every direction. So at the speed of light, it’d take at least 30 billion years to cross it. That’s about 16 billion years longer than the age of the universe itself.

Ah. So it’s big, then?Like I said, crazy big. And that’s just the part we can see. Beyond that, we know it extends even farther because the light from the stuff we can see at the “edge” has taken 14 billion years to reach us, and the universe has expanded quite a bit since then! It might even curve back on itself, like the sea does as you sail around the globe. If that were the case, you could circle the universe and end up back where you started.

Now that would be cool.Yes, it would. But all your friends would be billions of years older. So even if they were still around, they probably wouldn’t know what cool was any more. Bummer.
What is space made of?

Well, it’s not just “nothing.” Space is, at the very least, filled with gases spread out very, very thinly. It also bends—and possibly rips—so it must be made of something ...
But space is, well, space, isn’t it? No air, no gravity, ... Well, not exactly. Gravity is actually everywhere in space.Its pull becomes weaker the farther you move away from one particular source—like a planet—but it’s still there.And while it is true that there’s no air in space, there are other things spread around it. It’s only because the stuff is spread out so thin, and space is so big, that we can’t detect it very easily.

So what is this “stuff”?Mostly hydrogen and interstellar dust left over from the Big Bang.

How much of it is out there?Well, there’re billions of tons of it, but it’s spread so far and wide across the universe that you won’t find more than one atom per half a cubic inch of space in most places.2You’ve probably been told that gases spread out to fill their containers, right? Well, if there’s nothing else in the container, then they do. In this case, the container—the universe—was empty and is now at least 180 billion trillion miles wide. Spread over this distance, even billions of tons of material can look like virtually nothing. It just depends on how hard you’re looking for it.

OK ... so rather than say “there’s nothing in space,” you could say “there’s almost nothing in space” instead?Exactly. That will not only be more accurate, but it will also freak people out. Which is always fun.
Top 10 things to do in Space1. Float2. Drift3. Hover4. Do somersaults5. Spill some milk—and catch it again6. Play zero-gravity football7. Try to hit the Moon with a Frisbee8. Draw a halo above your head with toothpaste9. Wonder where your spaceship went10. Panic

Why do planets bother going around the Sun?

Because the Sun’s gravity pulls planets around it, preventing them from whizzing off into space. But despite this, the planets are still gradually inching away from the Sun over time.
Yikes. That doesn’t sound good. I thought we’d just go around and around the Sun forever.I’m afraid not. We’re getting a tiny, tiny bit farther from the Sun with each lap we do around it. The Earth gets about a half inch farther away from the Sun every year.

Why’s that?It all has to do with how gravity works. A very clever scientist named Isaac Newton explained how gravity works over 300 years ago. If, like me, you can’t read Latin and math gives you a headache, it basically goes like this: · Everything attracts everything else.· The bigger the things are, the bigger the pull.· The closer together the things are, the bigger the pull.· The force that causes this attraction is called gravity.Now, the Sun is by far the biggest object in the solar system, so it pulls everything else toward it. That includes planets, comets, asteroids—everything.Hang on a minute—so why don’t the planets all just get pulled right into the Sun?That’s because the planets all formed from chunks of stuff that were already circling the Sun to begin with. When the solar system began, these chunks clumped together to form planets and settled into regular circuits (or orbits) around the Sun. Closer to the Sun, all the icy bits got vaporized, so we ended up with the small rocky planets—Mercury, Venus, Earth, and Mars. Farther away, it was cool enough for gas to hang around, so we got the gas giant planets—Jupiter, Saturn, Uranus, and Neptune.

You forgot Pluto.No, I didn’t. Most astronomers don’t count it as a real planet these days. There are a whole lot of small Pluto-sized objects out there beyond Neptune, and these (it has been decided) aren’t planets either.

Oh.Anyway—as I was saying—the planets have settled into moreor-less fixed orbits around the Sun. They don’t get pulled right into it because they still have some circling speed (or rather, momentum)3 left over from when they were just baby chunks of planet (or planetesimals, as they’re called). It’s like they’re excitable puppies on a long leash—they’re trying to whiz off into space but the Sun’s gravity keeps pulling them around it instead.So why are they gradually getting away from it, then? Because the Sun is burning up its fuel and, in doing so, it’s shrinking. As it gets smaller, the strength of ...