Astrophotography

"Afterwards I had to clean my nose print off the window."

Auroras aren't all: "I've seen an occasional meteor while looking down through the Destiny Lab window," he says. Meteors disintegrate in Earth's atmosphere below the space station, so you have to look down to see them! "You can also see space junk orbiting nearby. Sometimes it flickers due to an irregularity catching light as it rotates. And there are satellites, too. A flash of sunlight glinting off an Iridium satellite near the Southern Cross really brought a smile to my face."

Auroras over Canada with the Manicouagan impact crater in the foreground. Clouds and Earth's surface are illuminated by moonlight. "Here in the same picture we have two interesting space phenomena: asteroid impact damage on the surface of Earth and auroras," notes Pettit.

Pettit recently took some lovely pictures of star fields in the southern hemisphere: the Large Magellanic Cloud (a nearby galaxy that orbits our own Milky Way galaxy), the Coal Sack Nebula (an inky-black interstellar cloud), and the Southern Cross.

"These pictures show how wonderfully stable the space station is," says Pettit. "When the camera is mounted to the window, the ISS itself serves as a tripod. Any movement would cause streaks in the star images." But the station's Control Moment Gyros maintain attitude with rock-solid precision. "I don't believe that the ISS was designed for astronomy," adds Pettit, "but it functions very well as a platform for astrophotography."

Credit: NASA and Don Pettit A snapshot of the Large Magellanic Cloud - an irregular galaxy visible from Earth's southern hemisphere.

One of the curious things about sky watching from orbit is the appearance of stars. "They don't twinkle," says Pettit. Twinkling is caused by irregularities in Earth's atmosphere that refract starlight to and fro. But in orbit there is no atmosphere. Stars are remarkably steady and piercing.

City lights, on the other hand, do twinkle. "From the space station we can see city lights when it's night-time on the planet below," explains Pettit. "Shining upwards through the atmosphere, they twinkle like stars. They're beautiful."