Why a Pale Blue Dot?

I just spent the last few days in a breathtakingly beautiful Chicago for the Pale Blue Dot III astrobiology conference. I met some brilliant astrobiologists and astrobiology graduate students, who manage to stay motivated and enthusiastic despite NASA’s significant cuts in the field. And they taught me SO much—about the Earth’s climate, the clouds of Venus, the rocks of Mars, the machines that can determine a distant planet’s surface chemistry by looking at just a speck of light, even the odds of getting hit by an asteroid.

But of all the tidbits I didn’t know Saturday and do know now, here’s the one I was most embarrassed not to know (and thought my faithful blog readers would most enjoy):

When viewed from space, the Earth looks like—to quote Sagan—a “pale blue dot,” not because of our vast oceans. No, the astrobiologts patiently explained, the oceans are actually very dark. We look blue for the same reason the sky looks blue when standing on earth: because the oxygen and nitrogen molecules that make up our atmosphere absorb short wavelengths—blue!—and not longer wavelengths like red. It actually gets a lot more complicated, of course, with details about cloud cover, but I'm pretty sure that was the jist.

The photo here shows the Earth and its moon as seen from cameras on Mars.