Striking pictures show the ISS crossing a sunspot big enough to swallow two Earths during a spacewalk

• Photos show the International Space Station crossing the sun.
• The rare pictures show the ISS while NASA astronauts were out on a spacewalk.

An astrophotographer has managed to take stunning pictures of the International Space Station (ISS) crossing the sun while astronauts were out on a spacewalk.

The ISS cast its shadow across three sets of sunspots, one of which was big enough to swallow two Earths whole.

At the time, NASA astronauts Stephen Bowen and Warren "Woody" Hoburg had just exited the station to install a new solar array.

Thierry Legault, a French astrophotographer, traveled six hours with his 220-pound telescope to capture the images of the ISS on June 9, a difficult feat when considering the ISS travels at about 17,500 mph.

"The transit lasts less than one second," he told Insider. He was lucky to snap the pictures as "45 minutes later a big cloud hide the sun," he wrote.

The ISS circles the Earth every 90 minutes or so, but it only spends about 0.75 seconds traveling in front of the sun, so only the most accomplished of astrophotographers can manage to snap high-resolution images like these.

Below, you can see how long Legault had to snap these arrays of pictures, in real-time.

In the footage above, the ISS is also seen crossing three sets of sunspots, which is, in itself, pretty rare.

Sunspots are areas where the sun's magnetic fields are particularly unstable, which can trigger solar flares, giant explosions that send energy and high-speed particles into space.

Solar flares have previously been known to cause radio blackouts on Earth as well as create stunning auroras.

Charged particles from solar flares can also pose some radiation risk to astronauts, especially if they are outside of the ISS on a spacewalk, according to NASA. That being said, scientists keep a close eye out for solar flares and NASA can cancel spacewalks before the particles reach the Earth's vicinity to keep the astronauts safe.

More sunspots and solar flares have been appearing on the sun as it reaches a decadal peak of activity.

While the ISS may look as if it's close to the sun in these pictures, that is just a trick of the camera. The ISS orbits the Earth about 250 miles above the ground, while the sun is about 93 million miles away.