How to See Comet SWAN in Night Skies


Even as humans on Earth remain locked down, the heavens abide. There is always reason to look up, perhaps now more than ever.

The latest evidence of this is the newly discovered Comet SWAN now streaking through the constellation Pisces. If you are fortunate to live in the Southern hemisphere and can find Pisces, you can see this comet, an chunk of dirty, very old ice shedding gas and dust as it nears the sun, as a pinpoint of light, about as bright as the dimmest stars visible to the naked eye.

Astronomers have their fingers crossed that the comet will keep brightening in the coming weeks as it heads north, passing 52 million miles from Earth on May 12 at its closest approach to our planet, and then rounding the sun on May 27.

Tony Philips, an astronomer and writer who runs the website, said he was cautiously optimistic of a big show in the weeks ahead.

“As for the cool-factor, I would give it a big resounding MAYBE :)” I wrote in an email. “It just depends on how the comet reacts to solar heating as it approaches the sun in the next few weeks.”

The comet could become a victim of the solar system’s ravages before more of us get to see it.

“Two brightness surges followed by drop in activity,” said Michael Mattiazzo, an amateur astronomer who lives in Adelaide, Australia, and first spotted the comet. “My guess is that it will outburst again before finally disintegrating.”

As recently as Friday, the comet was about as bright as the faintest stars that can be seen with the naked eye – 5th magnitude in astronomical parlance. Astronomers best guesses suggest that the comet will get 3 or 4 times brighter – up to astronomical magnitude 3.5 – as it moves northward out of Pisces and through the Triangulum and Perseus constellations.

But it will still be hard to see if you live in the mid-latitudes of the north. At its best, the comet will be hanging low in the northeastern sky just before dawn.

Rick Fienberg, spokesman for the American Astronomical Society said, “By‘ low ’they mean‘ really low ’unless you’re far south like Hawaii or southern Florida. The comet gets higher as dawn breaks, which means it’ll never appear in a dark sky for mid-northern observers. Boo hoo! ”

Later in May and into June, northerners will get another crack at seeing the comet just at evening twilight. By then it will be crossing from Perseus into Auriga, passing not far from the bright star Capella. But again it will be only a few degrees above the north-northwest horizon according to Sky and Telescope magazine’s viewing guide.

Bring binoculars if you want to see the whole show.

Comet SWAN’s discovery could be partly credited to the pandemic. Mr. Mattiazzo first spotted it in early April as the coronavirus lockdowns fully set in around the planet. “I work in the pathology industry, which, to the surprise of many, had a significant downturn in local inpatient and outpatient workload during the Covid crisis,” he wrote on his personal website.

The downtime gave him more time to hunt comets, an enthusiasm he had embraced ever since Halley’s comet came calling in 1986. To perform his own armchair comet seeking, he scanned images from the Solar and Heliospheric Observatory, a NASA and the European Space Agency spacecraft that orbits the sun about a million miles from Earth.

The spacecraft has a camera called SWAN, for Solar Wind ANisotropies, sensitive to ultraviolet light and used to look for hydrogen gas in the solar neighborhood. As Mr. Mattiazzo described it, “SWAN is great at detecting comets as they shine brightly in UV due to the sublimation of water ice when near the sun.”

Over the years he had discovered seven comets this way.

In early April, I found a little blob of light nobody else had noticed, on a photo taken on March 25.

Subsequent observations confirmed that it is a comet, officially tagged as C / 2020 F8 (SWAN), after the solar wind camera.

Comets originate as frozen chunks of gas and dust – planetary leftovers that have been sitting in a pair of outer-solar-system deep freezes known as the Oort cloud and the Kuiper belt, ever since the beginning of the solar system 4.5 billion years ago. Every once in a while, the gravitational nudge from a passing star dislodges one of these leftover snowballs and it falls sunward.

From what they know of its orbit so far, astronomers suspect that SWAN is one of these fresh comets, newly arrived from the outer realms of the solar system. Sunlight is probably touching its fragile, volatile surface for the first time, causing it to crack and boil off gas and shed dust.

The result of such a virgin experience can be spectacular, and to the ancients terrifying. Dust gets pushed by the pressure of the sun’s light into a bushy tail that gets left behind along the comet’s path and in decades to come is a source of meteor showers. At the same time, gases get ionized by the sun’s ultraviolet radiation and they line up with the sun’s magnetic field, often pointing in a different direction than the dust tail. The long tail presently sported by SWAN in astronomical photographs is such an “ion” trail.

Some models of Comet SWAN’s behavior have it peaking in brightness early in June, but comets are notoriously fickle.

Late in April another promising comet, ATLAS, fell apart and faded without ever becoming visible to the naked eye.

And that could happen to SWAN, too, but while you look for it, you’ll still get the best show the cosmos has to offer us. And you won’t need Wi-Fi either.