A rare, green-glowing comet will make its closest approach to Earth next week — and it won’t return for more than a thousand years.
Comet C/2025 A6 (Lemmon), described by National Geographic as “this year’s brightest comet visible from Earth,” will pass closest to our planet on Tuesday, Oct. 21, coming within about 55 million miles. Scientists say it’s an icy leftover from the early days of the solar system, making this a once-in-a-lifetime sight.
When and where to look
According to National Geographic and Forbes, Comet Lemmon will reach its closest point to Earth on Oct. 21, aligning with a new moon that will make faint celestial objects easier to see.
Skywatchers should look for a soft green glow low in the western sky shortly after sunset, near the constellations Scorpius or Libra. The comet, although will start to fade after Tuesday, should remain visible through early November.
Forbes notes that the comet will be about 55 million miles from Earth at its closest approach. It may be hard to see without help, but a good pair of binoculars or a small telescope should make it easy to spot from darker areas away from city lights.
Why it glows green
As National Geographic explains, Comet Lemmon’s vivid emerald hue comes from a gas called diatomic carbon, which shines green when sunlight hits it. The comet also has two tails — one made of dust and another made of gas — which can look blue as it gets closer to the sun.
A frozen time capsule
Comet Lemmon was discovered on Jan. 3, 2025, by the Mount Lemmon Survey near Tucson, Arizona, Forbes reports. Astronomers estimate that it takes roughly 1,150 to 1,350 years to complete a single orbit around the sun, meaning no one alive today will ever see it again.
According to NASA, recent images show the comet’s glowing green head and changing tail as it brightens on its way toward the sun. It’s expected to keep glowing until early November, when it will slowly disappear from view.
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