The lunar flights give you a correct perception of our existence. You look back at Earth from the moon, and you can put your thumb up to the window and hide the Earth behind your thumb. Everything you've ever known is behind your thumb, and that blue-and-white ball is orbiting a rather normal star, tucked away on the outer edge of a galaxy.

There is good evidence that Venus once had liquid water and a much thinner atmosphere, similar to Earth billions of years ago. But today the surface of Venus is dry as a bone, hot enough to melt lead, there are clouds of sulfuric acid that reach a hundred miles high and the air is so thick it's like being 900 meters deep in the ocean.

I watched the moon landing as a boy, and I thought that was the most exciting thing ever, going into space, orbiting Earth and exploring other planets. That looked fantastic.

Philosophically, the universe has really never made things in ones. The Earth is special and everything else is different? No, we've got seven other planets. The sun? No, the sun is one of those dots in the night sky. The Milky Way? No, it's one of a hundred billion galaxies. And the universe - maybe it's countless other universes.

The most important thing about Spaceship Earth - an instruction book didn't come with it.

In so many and such important ways, then, do the planets bear witness to the earth's mobility.

There is a project that's underway called the interplanetary Internet. It's in operation between Earth and Mars. It's operating on the International Space Station. It's part of the spacecraft that's in orbit around the Sun that's rendezvoused with two planets.

Mining asteroids will ultimately benefit humanity on and off the Earth in a multitude of ways.

Whenever I gaze up at the moon, I feel like I'm on a time machine. I am back to that precious pinpoint of time, standing on the foreboding - yet beautiful - Sea of Tranquility. I could see our shining blue planet Earth poised in the darkness of space.

During launch, the outside of the rocket is covered in a protective fairing, so we couldn't see outside, but as soon as that was jettisoned, my first view of the earth was over the Pacific Ocean, which was this wonderful deep blue, with clouds just over the top, and sunlight streaming in through the window.

When many astronauts go to space, they see the insignificant size of the earth and vastness of space, and they become very religious, because they have seen the Signs of Allah.

Mankind will not forever remain on Earth but, in the pursuit of light and space, will first timidly emerge from the bounds of the atmosphere and then advance until he has conquered the whole of circumsolar space.

It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn't feel like a giant. I felt very, very small.

Once you've been in space, you appreciate how small and fragile the Earth is.

What was most significant about the lunar voyage was not that men set foot on the moon but that they set eye on the earth.

If the Earth gets hit by an asteroid, it's game over. It's control-alt-delete for civilization.

The Earth is the cradle of humanity, but mankind cannot stay in the cradle forever.

One in 200 stars has habitable Earth-like planets surrounding it - in the galaxy, half a billion stars have Earth-like planets going around them - that's huge, half a billion. So when we look at the night sky, it makes sense that someone is looking back at us.

There are no passengers on spaceship earth. We are all crew.

We are not going to be able to operate our Spaceship Earth successfully nor for much longer unless we see it as a whole spaceship and our fate as common. It has to be everybody or nobody.

Men of genius are often dull and inert in society; as the blazing meteor, when it descends to earth, is only a stone.

How terribly downright must be the utterances of storms and earthquakes to those accustomed to the soft hypocrisies of society.

The official version of Watergate is as wrong as a Flat Earth Society pamphlet.

We're looking at Earth science, observing our planet. Also space science, looking at the ozone in the atmosphere around our Earth. Also looking at life science. And on a human level, using ourselves as test subjects.