I think everyone should have a personal mission to leave the Earth a better place for them having lived in it and let Earth then take it from there.

Some memories are best absorbed through your eyes in real time, even if you have no record of it later. Because then you can access that memory and how you felt in that moment. If you're looking at your cellphone screen, taking a video of something that is otherwise unforgettable, watching it later will not recover the emotion you would have had, had you witnessed it directly.

Trillions of years into the future, when all stars are gone...all parts of the cosmos will cool to the same temperature as the ever-cooling background. At that time, space travel will no longer provide refuge because even Hell will have frozen over. We may then declare that the universe has died-not with a bang, but with a whimper.

The chances that your tombstone will read 'Killed by Asteroid' are about the same as they'd be for 'Killed in Airplane Crash.'

Relativity. Gravity. Quantum. Electrodynamics. Evolution. Each of these theories is true, whether or not you believe in them.

We didn't go to the moon to explore or because it was in our DNA or because we're Americans. We went because we were at war and we felt a threat.

When Kennedy said, 'Let's go to the moon,' we didn't yet have a vehicle that wouldn't kill you on launch. He said we'll land a man on the moon in eight years and bring him back. That was an audacious goal to put forth in front of the American people.