From down here on the ground, space looks like a pristine void. But Earth's orbit is actually crowded with a ton of stuff, from human-made satellites to many smaller pieces of debris whirling around at dangerously high speeds, as the film Gravity so memorably dramatized. In fact, there are an estimated 500,000 or so smaller orbital debris (between one and 10 centimeters in diameter) and about 21,000 larger bits (larger than 10 centimeters) spinning around Earth right now, according to NASA's Orbital Debris Program Office.

Millions of years ago, slow changes in the Earth's orbit changed the climate in East Africa dramatically. Every 20,000 years ago, the region vacillated between very dry and very wet periods. These extreme changes may have played a vital role in driving human evolution, according to what's called the pulsed climate variability hypothesis.

At noon today, NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) was released from a companion aircraft and sent off into Earth's orbit. That's big news for black hole and space enthusiasts: The technology strapped to it will make the hunt for celestial objects significantly easier, both in the Milky Way and farther abroad.