I DIDN’T KNOW THAT . . .

Q: When we see pictures of Earth from space, why don’t we see stars?

A: Pictures of Earth taken from orbit don’t show stars because the Earth is too bright for them to be visible. When the lens of a camera is closed down enough so that clear pictures can be taken of Earth, too little light from the stars reaches the film for them to register. Spacecraft that get farther away from Earth, however, can take pictures that show both the Earth and stars because the brightness of the Earth decreases when you get farther away. The title of the late Carl Sagan’s book, “Pale Blue Dot,” refers to this phenomenon.