Comet E3 (ZTF)
© Bill WilliamsMulti-tailed Comet E3 (ZTF)!
Taken by Bill Williams on January 20, 2023 @ Chiefland Astro Village, Florida, USA
Astrophotography alert! Comet ZTF (C/2022 E3) is developing an anti-tail, and tonight may be the best time to photograph it. Unlike ordinary comet tails, which are blown away from the sun by solar wind and radiation pressure, anti-tails point toward the sun. That sounds impossible, yet Bill Williams just photographed the anti-tail of Comet ZTF from his observatory in Chiefland, Florida:

"Comet ZTF has developed an anti-tail in addition to its dust and ion tails!" says Williams. "Just how many tails can a comet have?"

Briefly, three. Comets sometimes grow an ephemeral third tail, the "anti-tail." It's an optical illusion seen when Earth crosses a comet's orbital plane. At that moment, the edge of the comet's fan-shaped dust tail looks like an sunward pointing spike.


Comment: No, it is not an 'optical illusion'. It is a sunward spike, as described by James McCanney.


"It's happening tonight," says longtime comet observer Paul Robinson of Longmont, CO. "On the evening of Jan. 22nd in the Americas, Earth crosses the orbit of Comet ZTF, which should produce a good spike. Photographers will not want to miss this!"

Robinson has been tracking comets since Kohoutek in 1974. "I have seen and predicted several orbital crossings--including Comet PanSTARRS in 2013, which crossed on May 26th, my birthday. I saw a 7 degree sunward spike in 25x100 binoculars that day."

Comet Arend-Roland
© Palomar ObservatoryThe iconic anti-tail of Comet Arend-Roland (C/1956 R1) in 1957.
"My estimates using Starry Night Pro 8 say that Comet ZTF's orbital crossing will take place at 11:30 pm EST on Jan. 22nd," notes Robinson. JPL's Horizons ephemeris suggests a slightly different time: 08:50 pm EST. The anti-tail should be sharp and bright throughout that time range.

THE LIGHT CURVE OF COMET ZTF

Multiple observers are reporting a surge in the brightness of Comet ZTF (C/2022 E3). In the past 48 hours, it has crossed the threshold of naked-eye visibility:
Comet E3 (ZTF)
The comet is approaching Earth for a close encounter (0.28 AU) on Feb. 1st. Forecasters expected it to reach magnitude +5.5 to +5.0. It appears to have hit that mark more than a week early. The sudden brightening makes Comet ZTF a barely naked-eye object in dark-sky locations, and an easy target for backyard telescopes anywhere--even downtown London!