The ionosphere is a layer of Earth's atmosphere that starts about 50 miles up and extends several hundred miles into space. What makes it special is that it's filled with electrically charged particles called ions, created when energy from the sun strips electrons off atoms in the thin air.

The ionosphere matters enormously for modern life because it bounces radio waves back to Earth like an invisible mirror in the sky. Without it, AM radio stations could only broadcast a few dozen miles. With it, radio signals can travel thousands of miles, allowing ships at sea to communicate with land, or letting you pick up distant radio stations at night when the ionosphere becomes more reflective.

The ionosphere is also where the aurora borealis (northern lights) appears. When charged particles from the sun collide with gases in the ionosphere, they create those shimmering curtains of green, red, and purple light in polar skies. GPS satellites have to account for the ionosphere too, because radio signals passing through it get slightly delayed, which could throw off location calculations by hundreds of feet if engineers didn't correct for it.

Scientists monitor the ionosphere constantly because solar storms can disrupt it, interfering with radio communications and navigation systems that ships, planes, and even your phone rely on.