Linda Piceno, age 13, of Santa Maria, Calif., for her question:

Why are stars in photographs like long streaks?

We observe the heavens from the surface of the spinning Earth. As the Earth spins, our view changes slightly every second. Every few moments a star shifts its position in the sky. It takes time to gather Enough light to photograph a star. In the time needed to make the exposure, the star has moved. It leaves a streak of light on the photographic p1ate.

Big telescopes are set with tracers that move them to keep pace with the their camera equipment will rotating Earth. They can fix on a distant star and/photograph it as a bright dots when a telescopic camera is photographing a comet, it is focused on a nearby object. The background moves during the exposure and the distant stars look like long streaks rather than dots of light.