A pair of once-in-a-lifetime comets are rocketing through our skies right now, and it's a rare treat because they won't be back for hundreds of years. The comets, C/2025 A6 (Lemmon) and C/2025 R2 (SWAN), look similar.
You can spot these green gaseous globes and their streaming tails right now, with SWAN shining the brightest on Monday, Oct. 20, NBC News reports. Just a day later, on Tuesday, Oct. 21, Lemmon will make its peak showing in the dark sky.
You'll be able to see Lemmon without any equipment, but SWAN will be pretty faint, says Jason Steffen, assistant professor of physics and astronomy at UNLV.
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"Current models are showing the [Lemmon] comet will likely peak between 3.5 and 4.5 magnitudes when it is nearest to Earth on October 21, which is dimmer than what they showed last week," Saint Louis Science Center wrote in an update. "This is still bright enough that it could become naked-eye visible from light-polluted locations."
CNN reports that SWAN will next come by again in 650 to 700 years, and Lemmon won't return for another 1,300 years.
"Comet Lemmon is called a non-periodic comet. Unlike Halley's comet, which comes around every 76 years, a non-periodic comet's orbit is really highly elliptical," Steffen says. "The last time it was here was in the 700s."
Comets are known to buck even the most careful predictions, but wary observers might catch these rare spectacles in October from their backyards in the predawn morning or night sky.
New comets on the scene
Lemmon and SWAN were both discovered in 2025. Lemmon was discovered on Jan. 3 in Arizona by the Mount Lemmon Survey using a 60-inch telescope installed on Mt. Lemmon to find celestial objects, which gave the comet its name.
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