Countdowns

The Mercury program launched the first Americans into space, four on suborbital flights, and two who orbited the Earth.

Here's where to go to get your space shuttle fix in museums across the United States.

Earth has been sending probes to Mars for decades, and some missions are especially awe-inspiring.

Here are some of the more prominent Mars movies over the decades, to encourage you to keep exploring.

The four Galilean moons of Jupiter are Io, Europa, Callista and Ganymede.

Almost 100 missions have been sent to the moon. Here are some of the best.

Nine exceptionally bright "Great Comets" have been visible to the naked eye over the past 300+ years.