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You'd think we'd know all about our home planet. After all, we live on it. And, we do know quite a bit, just from walking its surface, sailing its oceans, and flying in its atmosphere. But, as any traveller knows, distance lends perspective. It gives us new insights into familiar places, simply by virtue of the fact that we are far away and can perceive home as a place "back there." You see a bigger picture of your hometown when you're far away from it. And, so it's the same with our planet.
Earth, as seen by the Galileo spacecraft on December 11, 1990.
I've been working on a project focused on our planet's climate and so I keep returning to these pictures taken from well away from Earth's surface. The first thing you notice is the water. And then, the clouds. Which, in our case, also speak of water, but in droplet form suspended in our atmosphere. Here and there the continents and islands peek out, and if you're close enough, you can see the lush green of plant life. It's home, but it's also part of the larger universe. The same laws of physics and astrophysics that operate across the cosmos govern our solar system and home planet. What we observe here we can try to find elsewhere. And if we do find watery, lifebearing planets elsewhere, we may understand them better simply by virtue of studying our own world from a distance, too. And, in a sense, what we find at THOSE worlds, will also help us understand our own.
Voyager's view of Earth from the "edge" of the solar system.
Earth is an amazing find in a universe populated mostly with galaxies studded with stars and nebulae. There are other planets out there, and most likely many with water and life. We haven't found the life-bearing ones yet, but it's only a matter of time. Until we do, that pale blue dot in the middle of the ray of light on the right is a rarity. It's also one of my choices for one of the seven wonders of the universe.
The Layers of our atmosphere From NOAA via Wikipedia
People tend to think of "outer space" as "out there." Way far away. Light-years away maybe. But, it actually starts much closer to us than we think. The classical definition that describes the interface between our atmosphere and space where space starts is that "outer space" begins where our atmosphere is completely thinned out. That's at 100 kilometers (62 miles) overhead. If you happen to fly over that limit, then you're an astronaut. If you fly below it, you're a high-altitude flier (whether passenger or pilot).
So, once we get above that level, we're in outer space. Where does it end? Well, it stretches on throughout the cosmos, but when you land on another planet, you've left outer space and you're back into a planetary atmosphere. On Mars, for example, you'd be inside the atmosphere at 11 kilometers (about 7 miles).
Earth's atmosphere is pretty darned narrow when you look at it against the limb of our planet. All the life we know about, everybody we know or have known, or who has ever lived on this planet, did it inside a thin envelope of air that starts to thin out a few miles over our heads. The gravity of our planet holds the atmosphere pretty firmly in place, and radiation and particles from the Sun interact with the top of the atmosphere. It's a lively place, this interface between Earth and space.
"Top of the Atmosphere" courtesy NASA.
I've been reading with some interest about the companies that want to start up space tourism. There's a company in Florida that flies people through our atmosphere in a commercial "Vomit Comet" so they can experience several minutes of weightlessness. But those still fly inside our atmosphere. SpaceShipOne, designed by Burt Rutan, made the first non-governmental human spaceflight on June 21, 2004. There will be others, and perhaps in my lifetime, regular people will be able to take off and experience "outer space" for themselves. I hope I can be one of them.
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Adot's Notblog A fellow traveler blogger and astronomy enthusiast!
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The Layers of
