Some molecules - ammonia, carbon dioxide, water - show up everywhere in the universe, whether life is present or not. But others pop up especially in the presence of life itself. Among the biomarkers in Earth's atmosphere are ozone-destroying chlorofluorocarbons from aerosol sprays, vapor from mineral solvents, escaped coolants from refrigerators and air conditioners, and smog from the burning of fossil fuels. No other way to read that list: sure signs of the absence of intelligence.

The Venus transit is not a spectacle the way a total solar eclipse is a spectacle.

Where did the concept of "without borders" come from? No one had that concept until you saw Earth from space, illustrated not by a mapmaker who's color-coding political boundaries; it's illustrated by nature itself and there's land, there's ocean, there's atmosphere.

If the only time you think of me as a scientist is during Black History Month, then I must not be doing my job as a scientist.

When everyone agrees to a single solution and a single plan, there's nothing more efficient in the world than an efficient democracy.

In any city with lots of skyscrapers, lots of skyline, the moon seems bigger than it is. It's called the moon illusion.

It is astonishing to realize that until Galileo performed his experiments on the acceleration of gravity in the early seventeenth century, nobody questioned Aristotle's falling balls. Nobody said, Show Me!