"I saw for the first time the earth's shape. I could easily see the shores of continents, islands, great rivers, folds of the terrain, large bodies of water. The horizon is dark blue, smoothly turning to black. . . the feelings which filled me I can express with one word--joy." -Yuri Gagarin

It takes a tremendous amount of energy to do any type of heavy lifting, and the most extreme example of this is lifting something all the way up off of the Earth, out of the atmosphere, and into space!

And once you're up there, at least 300 km above the Earth's surface, the sights you've got are bound to be absolutely amazing! For example, if you took the US Space Shuttle up, you'd likely dock with the International Space Station, and get to see something as breathtaking as this:

But gravity is a funny thing. The same force that pulls the Moon into our planet's orbit is trying to pull your orbiting body (and whatever spacecraft it's inside) back towards Earth.

But while the Moon is 384,000 km away from the center of the Earth and takes about four weeks to orbit the Earth, these man-made satellites and space vehicles, at an altitude of around 300 km, are only 6,700 km away from the center of the Earth.

(Image credit: Boeing.)

But one of the incredible things that our laws of gravity tells us is that, no matter what distance you are away from any mass, there's only one speed that will keep you moving in a stable, circular orbit!

Any guesses as to what that speed is at the altitude of the International Space Station?

It turns out that you need to travel at a whopping 27,700 km/hr (~17,200 mph) to stay in orbit around the Earth; any slower and you'll fall back down!

But let's take a look at the Earth itself. Although it's a pretty big place, it's only about 40,000 km all the way around; even at an altitude of 300 km, that makes an orbit of only about 42,000 km all the way around!

This means that it only takes about 90 minutes to make a complete orbit of the Earth, or, in Little Prince terms, you get about 16 sunsets per day.

What would it look like, if you were up on the ISS, as you went from Sunset to Sunrise, and got to look at the Earth from space during an entire 40-minute night?

Well, thanks to astronaut Don Pettit, who took a series of images every 15 seconds and stitched it together into a video of one "night" on the ISS, we can see for ourselves!

On a first viewing, I see that it starts out as "day" on Earth. We then get a sunset (and the accompanying lens flare), and then the night side of Earth, pock-marked by cities (the bright lights) clearly shows itself to us. The Moon rises, and the Aurora Borealis (I think) makes an appearance, not just once but twice! And then we pass over some more land (and see some more cities), and finally the Sun rises. Plus, near both sunrise and sunset, you can see the upper atmosphere turn an orange-red color!

And, from up in low-Earth orbit, astronauts get to see this sixteen times a day, speeding at over 27,000 km/hr. Pretty amazing stuff; and thanks to NASA's Solar Dynamics Observatory for posting the video!