Astronauts are many things. They're often scientists, engineers, or pilots. And in the case of NASA astronaut Don Pettit, he's also an astrophotographer.
Pettit is currently on his third stay on the International Space Station (ISS), and he's continuing his long-running tradition of taking out-of-this-world photos (pun intended). His latest shot, an image of the stars and several galaxies , showcases not only his visual prowess, but also his engineering skills — he used a self-designed tool to accomplish this photo. At first glance, the image might look like a rather typical shot from the ISS: You see stars and the curvature of Earth , with a distinct orange glow above our planet's surface.
But there's something strange about the photo: The surface of Earth is blurred, yet hundreds if not thousands of stars are in perfect focus. Under normal circumstances, long-exposure photographs such as this should show the stars as streaks across the sky, since the ISS is moving at about 17,500 miles per hour (28,000 km per hour). But therein lies Pettit's genius.
He's brought with him to space a homemade star tracker , a device that rotates a camera to compensate for the ISS's movement. It's a variation on a tool used by astrophotographers on Earth to take long exposures of the stars as the planet rotates beneath the night sky, compensating for that rotation to keep the stars from becoming streaks in the image. "This tracker rotates at 90 min [sic] period to match the pitch rate of ISS.
