A rare comet glowing green will approach Earth next week, and will not return for more than a thousand years.
Comet C/2025 A6 (Lemmon), described by National Geographic as “the brightest comet seen from Earth this year,” will pass by our planet on Tuesday, October 21, about 55 million miles away. Scientists say they are icy remains from the early days of the solar system, making this scene a once-in-a-lifetime occurrence.
When and where to look
according to National Geographic and ForbesComet Lemmon will make its closest approach to Earth on October 21, aligning itself with a new moon that will make faint celestial objects easier to see.
Sky watchers should look for a soft green glow low in the western sky shortly after sunset, near the constellation Scorpius or Libra. Although the comet will begin to fade after Tuesday, it will remain visible until early November.
Forbes indicates that the comet will be about 55 million miles from Earth at its closest point. It may be difficult to see without assistance, but good binoculars or a small telescope will make it easier to see in dark areas away from city lights.
Why does it light up green?
As National Geographic explains, Comet Lemmon’s vibrant emerald color comes from a gas called diatomic carbon, which glows green when sunlight hits it. The comet also has two tails, one made of dust and one made of gas, and can appear blue as it approaches the Sun.
A frozen time capsule
Comet Lemmon was discovered on January 3, 2025, by the Mount Lemmon Survey near Tucson, Arizona, Forbes reports. Astronomers estimate that it takes approximately 1,150 to 1,350 years to complete one orbit around the Sun, meaning no one alive today will see it again.
according to NASARecent images show the comet’s glowing green head and changing tail as it brightens on its way toward the sun. It is expected to continue glowing until early November, when it will slowly disappear from view.