字幕表 動画を再生する 英語字幕をプリント If you could teleport the Earth to any place in the Universe, what would you want to look at in the night sky? The bright explosion of a supernova? A black hole passing over your house? How about a nebula? This is WHAT IF, and here's what would happen if we lived inside of a nebula. What is a nebula anyway? A nebula is a giant cloud of dust and gas in interstellar space. They are vast, sometimes taking up hundreds of light-years of space. But with all that size, they aren't massive. A nebula the diameter of the Earth would only have a mass of a few kilograms. That's because nebulae aren't very dense. And that's why, if we lived inside one, it wouldn't look anything like what you might expect. Some 1,344 light years away from Earth, is the Orion Nebula - the brightest nebula in our sky. It's 24 light-years across, and has a mass equivalent to 2,000 Suns. If the Earth was formed inside it, all you'd see in the night sky would be this. Not impressed? I know, I wasn't either. It turns out it's not that easy to see a nebula when you look at the night sky. To your eye, most galaxies in the Universe don't look anything like this. More like this. And most nebulae are invisible altogether. Your eyes aren't sensitive to the kind of light a nebula produces. But look at the image taken by the Hubble Space Telescope, and you'll see a beautiful gas cloud. That doesn't mean these beautiful images of space are fake. Their colors just represent the lightwaves that your eyes aren't able to detect. So, if you had the Hubble Telescope, would you be able to see a nebula if you lived in one? Sorry to disappoint you again, but no. Nebulae are pretty only when they are hundreds of light-years away. They look thick and cloudy only because you see the structures of light-years in thickness. Once you're close to them, their light spreads out so much that you can't see them. You could fly your spaceship right into the nebula and never even know it. If the Earth were inside a nebula, the only effect you'd see would be brighter Auroras. Unless the solar wind blew all the nebular particles far away from the planet. How do we know we are not living inside a nebula right now? Simple. After gathering the data on our own Sun, we can calculate the expected brightness of the neighboring stars. If we did live inside a nebula, we'd notice that our star was much brighter compared to others. The nebula would be dimming the light coming in from outside of it. But don't be sad. We can't teleport the Earth, yet. But we may be able to travel to distant exoplanets that experience incredible light shows in the night sky. But that's a story for another WHAT IF.