An astronaut has wowed the internet by capturing an image he says most space photographers "can only dream about"—star trails from space.
The space photo was captured by Donald Pettit, an active NASA astronaut who has traveled to the International Space Station (ISS) on three separate occasions.
Pettit, a keen astrophotographer, would use his free time during missions to snap photos of space from inside the station's cupola—a small glass dome made of seven windows that allows astronauts to observe space and the Earth from orbit.
During his last visit to the station in 2012, Pettit set up his Nikon D3s camera in the cupola and left it to take in all the light it could in a 15-minute exposure shot. The result can be seen below.
The photo is blurred deliberately due to the camera continually taking in light for 15 minutes, allowing it to capture motion. The white lines at the top of the image are the trails of distant stars, curved due to the rotation of the space station as it orbits the Earth.
The bottom half of the image shows the Earth itself, with orange streaks of city lights and countless blue dots—each a lightning strike from a storm below.
Pettit posted the photo, which he calls Lightning Bugs, to Reddit on September 11, 2022. By September 21, it had gained over 68,000 likes and hundreds of comments from users.
Speaking to Newsweek, Pettit—now back on Earth—discussed the context behind the photo.
"We work 12- to 14-hour days six days a week on station, and outside of that you are off duty," he said. "Outside of your normal working hours, you can do whatever you want to, which includes sleeping and eating and staying in touch with your family. And then you can spend that time doing photography. If I could do a couple hours' of photography a day, that would be a real treat."
One limiting factor is that the conditions aren't always right for a photo. The ISS orbits the Earth once every 90 minutes. Of that, there are around 30 minutes in which the ISS is in the shadow of our planet, free from the sun's glare.
It's worth the wait, though. "The stars don't twinkle because the twinkling is an atmospheric phenomena, and the stars are brighter than what you're used to, and they're more colorful," Pettit said.
One notable feature of the image is the green glow that separates the Earth from space. This is a phenomenon called airglow, and it can be similar in color to the shimmering night-sky lights known as the auroras—the Northern and Southern Lights.
However, airglows and auroras are separate phenomena, driven by different processes.
"Auroras are excited by electrons, and other solar particles coming down Earth's magnetic fields, which is why you see them in the polar regions," Pettit said. "Air glow is everywhere around on Earth and, and the molecules in the upper atmosphere get excited from solar activity."
This causes the molecules to collapse to a ground state. An atom is in a ground state when it is at its lowest possible energy as defined by the orbits of its electrons. If an atom enters its ground state from a more excited state, it typically gives off a photon of light in the process.
