BY THE OPTIMIST DAILY EDITORIAL TEAM
Every so often, the cosmos offers a rare spectacle that feels timeless yet brand new. This spring, that spectacle is comet C/2025 F2 (SWAN)—a brilliantly green cosmic visitor currently visible in the early morning sky for those in the Northern Hemisphere.
“A new comet is always exciting. They appear unexpectedly. They’re quite beautiful,” says Paul Wiegert, an astronomer at the University of Western Ontario. “They do tell us a lot, too, about our solar system and about how the planets formed. So, you know, it’s sort of a beautiful addition to our springtime skies.”
The story behind the green glow
Comet SWAN was first spotted in late March by amateur astronomer Michael Mattiazzo, who noticed it in images captured by its namesake, SWAN (Solar Wind ANisotropies), a camera aboard the SOHO spacecraft. Ukrainian astronomer Vladimir Bezugly also independently discovered it. Since then, astrophotographers have been quick to capture its dazzling presence.
What makes this comet particularly striking is its emerald glow. According to astrophotographer Mike Olason, “The green coma [the comet’s dusty glow] is the result of diatomic carbon being ejected from the comet’s surface. Sunlight destroys the diatomic carbon in the comet’s coma, which is the reason one never sees a comet with a green tail.”
Though its tail isn’t especially bright or wide, it still stretches significantly across the sky. Michael Jäger, another astrophotographer, estimates that the faint tail spans about two degrees of the night sky—roughly twice the width of a pinky finger held at arm’s length.
A path that brings it close—then far, far away
Comet SWAN is currently en route to its perihelion, the closest point to the sun in its orbit, which it will reach on May 1. As it moves closer, astronomers expect the comet to brighten.
“We expect it to get brighter, not because it’s necessarily getting more solar heating and being more active… but our geometry relative to it, we’re going to get closer to it,” Wiegert explains. “And all of those details are going to work in its favor.”
Astrophysicist Asa Stahl writes for the Planetary Society that while it might brighten enough to be seen with the naked eye, comets are “notoriously” difficult to predict. In some cases, they can break apart as they near the sun. As Stahl puts it, “only time will tell.”
How to catch a glimpse
For those eager to see this once-in-a-lifetime event, now is the time. According to Space.com’s Joe Rao, Northern Hemisphere skywatchers with binoculars or small telescopes can spot the comet shortly before sunrise along the northeast horizon until around April 25. After that, it shifts to the west-northwest horizon and will be visible after sunset until roughly May 5.
Southern Hemisphere observers should have their chance beginning around May 4.
And once it’s gone, it’s truly gone—at least for us. C/2025 F2 (SWAN) completes an orbit around the sun only once every 1.4 million years. So if you miss it this time, there won’t be a second chance.
