Is that what your teacher said? That’s why you’re upset? Well, it’s a great question. But...before I answer it, your Grandpap is going to tell you a story from a long while back, when he was your age:
Well, we had a dog, a fat old mutt named Chestnut, who spent most of his time sitting under the kitchen table looking for scraps. He wasn’t the smartest to be honest...he didn’t know any tricks or anything. I mean we tried to teach him, but he...well he just wasn’t very smart. We loved him though. If we were in the kitchen, a cold cut always found itself “accidentally” dropped on the floor. He was such a fat dog.
Anyways, we had him tied up out back one night. He always loved being out on hot summer nights, which I never understood because there were so many bugs out. You stayed still for a few seconds and your face was just covered in bugs. But regardless, he loved sitting out there. So on this night, I hear Chestnut barking like crazy, so I go out to see what’s got him so wound up. Well there was no mistaking what was driving him so nuts; the full moon was out. I’d never put much thought into it, you know I’d always figured a dog barking at the moon was just something that was only true in the movies and comic books.
But the thing is, it happened the next night too, and the night after that. The dog just went wild, and his eyes were just...just fixed on the moon. This is coming from the lazy old farty dog I’d known as long as I could remember, so as you might imagine, I was a little confused. This went on for four nights, and I remember my parents were furious. My brother and sisters and I were in a panic over the dog. But on the fifth night, we didn’t hear a peep, and we all looked out back to see what the dog was doing. He was gone! He’d freed himself somehow, and ran away.
We were all scared for him and worried for a few days, but then...something happened. Something, well it’s just about the strangest thing I’ve ever experienced. We looked up at the moon, and it was all chewed up! Before then, before that day, the moon was just a big white circle in the sky, nothing really distinctive about it. But if you look up at it now, it looks all chewed up, right? Turns out Chestnut had chased down the moon and gnawed on it a little. Scientists were all baffled.
And it didn’t stop there. A few weeks later, some astronomers saw that one of Mars’ moons, Phobos, had a big bite taken out of it. And a few weeks after that, Uranus seemed to have been tilted on its side, like something had pushed it around a little. And this kept happening over the years with stars and nebulae and all sorts of things, and of course it was all our fat old dog.
So, back to your question. Your science teacher was right, our Milky Way galaxy is on a crash course with the larger Andromeda galaxy, and in a few billion years there may be fiery and cataclysmic collision. What your science teacher didn’t tell you- what she didn’t know- is that between our galaxy and Andromeda is Chestnut, and I suspect he’s developed an even bigger appetite after snacking on moons and planets. You’ve got nothing to worry about.