Sometimes the universe surprises you when you are not even looking for it.
Nasa astronaut Chris Williams was aboard the International Space Station (ISS) on a fairly routine sky-watching mission, trying to photograph meteors from the Lyrid meteor shower.
The Lyrids are an ancient annual spectacle.
Every April, Earth passes through a trail of debris left behind by Comet C/1861 G1 Thatcher, a comet that was last seen in 1861.
The tiny fragments of that old comet enter our atmosphere and burn up as streaks of light.
Williams, peering out through the Cupola, the station’s stunning dome-shaped observation window, was hoping to catch some of those streaks on camera. What he captured instead was something far more dramatic.
Framed awkwardly near the base of the Canadarm2, the ISS’s iconic robotic arm, was the glowing tail of Comet C/2025 R3 PanSTARRS.
Williams had very nearly missed it. He managed to photograph it using a Nikon Z9 camera with a 200mm lens.
WHAT EXACTLY IS COMET C/2025 R3 PANSTARRS?
Think of a comet as a giant dirty snowball, or a clump of ice, rock and dust that travels around the Sun on a long, looping path.
Comet C/2025 R3 PanSTARRS is what scientists call a hyperbolic Oort cloud comet, which means it originates from the outermost, most distant region of our solar system. It has never visited the inner solar system before.
The comet was first spotted on September 8, 2025 in images from the 1.8-metre Ritchey-Chretien telescope at Haleakala, Hawaii, as part of the PanSTARRS survey, at a faint apparent magnitude of about 20.
This is invisible to the naked eye. The PanSTARRS project, as Williams explained in his post, uses two telescopes with wide fields of view to photograph large portions of the night sky every night, comparing new images to old ones to flag anything that has moved or appeared fresh.
HOW BRIGHT DID THE COMET GET?
On April 11, 2026, the comet was spotted with the naked eye, with an estimated magnitude of 5.1.
Its nucleus, the unseen frozen core, is likely just a few kilometres across.
As the Sun warms it, neutral gas forms a glowing cloud called a coma, which glows light green.
Solar radiation then ionises some of that gas, and the solar wind, a constant stream of charged particles from the Sun, pushes it away into a long, wispy blue ion tail.
The comet reached perihelion, its closest point to the Sun, on April 19, 2026, passing at a distance of roughly 74.6 million kilometres from it.
Its closest approach to Earth will happen on 26 April 2026, at a distance of roughly 73.2 million kilometres.
WILL THE COMET EVER RETURN?
Almost certainly not. Its future trajectory shows it being ejected from the solar system entirely.
This is a once-in-a-civilisation visit, and Williams caught it on camera from 400 kilometres above the Earth.
