A pair of once-in-a-lifetime comets is 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. Both comets have already had their brightest nights on Oct. 20 and Oct. 21. But if you're out and about this final week of October, you can still spot these green gaseous globes and their streaming tails.

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. 

 

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."