gold comet now?

A RARE GOLDEN COMET: Most comets are green, and sometimes blue. In June Lake, California, amateur astronomer Dan Bartlett is tracking a rare golden comet. Introducing, Comet ATLAS (C/2025 K1):

"This comet was not supposed to survive its Oct 8th perihelion (0.33 AU)," says Bartlett. "But it did survive, and now it is displaying a red/brown/golden color rarely seen in comets."

What's going on? The chemistry of this Oort Cloud comet is strange. It lacks the carbon compounds normally found in comets, according to spectroscopy by David Schleicher of the Lowell Observatory. "All of the carbon-bearing species, including CN, are unusually low," he wrote in Astronomer's Telegram #17362.

In sunlight, cometary gases turn green because of diatomic carbon (C2), and blue because of ionized carbon monoxide (CO+). Subtracting these colors apparently leaves gold. We don't know exactly why--or if it may have something to do with its recent close encounter with the sun.

"The comet is fairly impressive at 9th magnitude," says Bartlett. That makes it a relatively easy target for backyard telescopes.  Point your optics to the boundary between Virgo and Leo in the eastern sky shortly before sunrise. Sky maps: Nov. 2, 3, 4, 5, 6, 7.

more images: from Chris Schur of Payson, Arizona; from Richard Sears of Ballico, California

Signs in the sky? Comet Lemmon (C/2025 A6)

 

MARS ROVER SEES COMET ATLAS: Last week, interstellar comet 3I/ATLAS flew past Mars. Perseverance saw it. NASA has just released two photos from the rover’s Navigation Camera (Navcam): #1, #2. The images aren’t visually spectacular, but they do underline the comet’s proximity to the Red Planet. From Mars, 3I/ATLAS glowed at magnitude +6.7--about 90 times brighter than it appeared from Earth. The fact that Perseverance could capture it with a camera not designed for astrophotography bodes well for the much more sophisticated data being gathered by the orbiting Mars Fleet.

DON'T FORGET COMET LEMMON: With so much attention on interstellar Comet 3I/ATLAS, it is easy to forget a local comet brightening so rapidly that ordinary sky watchers will soon be able to see it with their own eyes: Comet Lemmon (C/2025 A6). It is falling toward the sun for a close encounter near the orbit of Mercury on Nov. 8th.

"This comet is developing very nicely and it is already an impressive object, well-placed for observation in the morning sky," says Nick James of the British Astronomical Association. "It is definitely worth getting up for!"

The light curve of Comet Lemmon shows that it is about to cross the threshold (m=+6) of naked-eye visibility:

"I think we can now be reasonably confident that this will be a very nice evening object when it is at its brightest around New Moon in late October," says James.

Not only is this comet bright, but also it is remarkably active. In recent nights, amateur astronomers have watched dozens of gaseous knots and filaments billowing down Lemmon's tail. Here's a freeze-frame on Oct. 5th from Italian astronomer Rolando Ligustri:

The ever-changing structure in the comet's tail is a likely result of two factors: Buffeting by the solar wind and dynamic jets in the comet's core. They're combining to make this a very satisfying target for astrophotographers.

Finding Comet Lemmon is easy. It's in the constellation Ursa Major (the Big Dipper) near the 3rd magnitude star mu Ursa Majoris. For most observers in the northern hemisphere, it is located well above the eastern horizon before sunrise. Sky maps: Oct. 5, 6, 7, 8, 9, 10, 11, 12, 13.