Where to watch rare green comet on once-in-a-lifetime pass by Earth
A unique green comet passing by for the first time since the Stone Age is making its closest approach to Earth this week, even visible to the naked eye for some viewers. And those curious to see it should grab the chance, because it won’t return in our lifetime — or perhaps ever, Bay Area astronomers say.
Known as C/2022 E3 (ZTF), the comet was discovered last March by the Zwicky Transient Facility in Southern California, according to Geoff Mathews, an astronomy instructor at Foothill College in Los Altos Hills.
Data has confirmed that the comet originated in the Oort Cloud, “a collection of icy bodies orbiting the sun at the outer fringe of the solar system” — a common source for the cosmic ice balls, said Gerald McKeegan, an adjunct astronomer at the Chabot Space & Science Center in Oakland.
“It is therefore likely that this comet is in a closed orbit and previously passed through the inner solar system about 52,000 years ago,” he said.
While a comet on such a closed elliptical orbit could be expected to return again tens of thousands of years in the future, its path could be interrupted by gravitational pull from other heavenly bodies, and by its own evaporation. The comet could then change or extend its orbit by millions of years, or even end up in a hyperbolic orbit — meaning it gains enough speed to escape the sun’s gravity entirely and exit the solar system.
This comet is “right on the edge,” Mathews said.
“While it currently appears to be on a ‘gone forever’ path, it is also likely that it will shift onto a returning orbit in the tensof-millions of years range, thanks to the extra gravitational tugs from the planets,” he said.
What’s certain, scientists agree, is that this is the last chance to see C/2022 E3 (ZTF) for anyone currently on Earth.
The comet is generating buzz because of its glowing hue. NASA and others have released telescopic photos of its brighter green coma — the gaseous cloud around the comet’s nucleus — its shorter dust tail and longer, faint ion trail.
McKeegan says it’s actually “quite common” for comets to appear to Earth observers as green or blue.
Comets are made up of several different kinds of ice, he said. As they approach the sun, the ice heats up and turns to gas, which forms the comet’s tail. Some forms of comet ice contain carbon compounds that in gas form appear greenish or bluish as they reflect sunlight.
C/2022 E3 (ZTF) rounded the sun in midJanuary, and its brightest and closest approach to Earth will take place Wednesday, Feb. 1. Experts say it will be visible for several days before and after that date.
“From a very dark sky location, it may be visible to the naked eye,” McKeegan said. “But for most locations, observers will need binoculars or a small telescope.”
With such viewing aids, Mathews said, it can be seen through the end of February.
To spot the comet, he said, look in the northeastern sky after 9 p.m. It will get progressively higher each day and will be almost directly above the North Star at around 10 p.m. Tuesday.
“Just look straight at the star and tip your head up a little bit, about twice the width of your outstretched fist,” he instructed.
Clear skies are also key, so clouds, haze or fog will hinder viewing. Fortunately, after a cloudy and rainy weekend, patchy clouds Monday will give way to partly cloudy to mostly clear skies through most of the week in the Bay Area, according to Chronicle newsroom meteorologist Gerry Díaz.
Foothill College and the Peninsula Astronomical Society are hosting a Comet C/2022 E3-focused event at 6:30 p.m. Tuesday, Jan. 31, at Foothill Observatory. The comet will also be visible during regular Friday night viewings from 9 to 11 p.m. through the end of February.
Chabot Space Center hosts free telescope viewing in its three observatories on Fridays and Saturdays, from 7:30 to 10:30 p.m.
If you miss this particular comet, Mathews offers some comfort: “Fortunately, our solar system was very messy when it formed planets 4.5 billion years ago, so there will be many more comets for us to see,” he said.