From the International Space Station, astronaut Don Pettit got a unique view of colorful auroras that sometimes dance above Earth's polar regions. He saw them on Earth's endless horizon. He looked down into them. He flew through them.

Auroras occur when elevated solar activity accelerates tiny, charged particles to race along Earth's magnetic field lines toward the poles. These particles excite molecules in the upper atmosphere, causing them to glow.

From Earth's surface, people at high latitudes sometimes witness the aurora from below. Pettit, the science officer for Expedition Six, got an edge-on view of the undulating, ephemeral phenomena, allowing him to estimate how high they go.

Green is the predominant auroral color, but reds are fairly common. Blue and yellow sometimes show up. Oxygen is the primary fuel for the lights, and nitrogen is involved, too.

Green emissions ranged from about 62 miles (100 kilometers) above the surface to about 186 miles (300 kilometers), Pettit writes in an account published by NASA last week. Red emissions danced always atop the green and extended up to 311 miles (500 kilometers).

Sometimes the orbiting outpost flies right through an auroral display (it orbits at about 250 miles, or 400 kilometers, up). Pettit's reflections on one such journey:

"We were in a dimly glowing fog of red. It was like we had been shrunk down to some miniature dimension and inserted into the tube of a neon sign. And it was just on the other side of the windowpane ... we wanted to reach out and touch! Afterwards, I had to clean a nose print off of the window."