Bright Comet SWAN Will Soon Grace May Mornings

Radar image of 1998 OR2 taken by the Arecibo Observatory on April 18, 2020. Arecibo Observatory / NASA / NSF

This morning (April 29) the large and bright asteroid 1998 OR2 will safely zip past Earth at a distance of 3.9 million miles (6.3 million km), equal to 16 times the distance to the Moon. While asteroids have passed much closer than this — including several that have brazenly crossed through geostationary belt of satellites around 22,000 miles away — this one’s unusual because it’s unusually large and therefore bright with a diameter of about 1.3 miles (2.1 km).

If you have at least a 4.5-inch telescope I encourage you to check out this story I wrote for Sky & Telescope. It includes more details and a chart to help you find and track the speedy object which currently shines at magnitude 10.9. But that’s not the biggest news I wanted to share today. We’re long overdue for a naked-eye comet, and I’m happy to report that one is on its way!

Comet SWAN (C/2020 F8) displays a green coma from fluorescing carbon gases and a long thin tail pointing southeast in this picture taken on April 18. The comet is now visible with the naked eye from dark Southern Hemisphere locations but will soon be visible in from northern latitudes. Damian Peach

Comet C/2020 F8 SWAN was found by Michael Mattiazzo, an Australian amateur astronomer, on photos taken with the Solar Wind ANisotropies (SWAN) camera on the Solar and Heliospheric Observatory (SOHO). The comet brightened quickly and glows at magnitude 5.5 as of April 29, bright enough to see with the naked eye from rural skies as a dim fuzzball. It’s expected to brighten a couple more magnitudes to 3.5, making it easily visible in binoculars in average skies and without optical aid from the countryside.

For now it’s only visible from the Southern Hemisphere. But SWAN is quickly moving to the northeast and will soon become visible for observers in mid-northern latitudes which includes the U.S., Europe and southern Canada. Amateur astronomer Piqui Díaz, who I correspond with from the southern hemisphere, easily found it with standard 50mm binoculars this morning (April 29) from her home in a light-polluted suburb of Buenos Aires, Argentina. She saw a very short tail and noted that the coma or head of the comet glowed pale green.

Comet SWAN will cruise low across the east and northeastern sky during May. Its position is shown every three mornings at 5:00 a.m. Central Time. The four stars in the Great Square will help point you to the comet. I also labeled other helpful stars with their Greek letter designations. Stellarium with additions by the author

Other observers under darker skies have traced the tail to more than 3° or six full-moon diameters. Wow, I can hardly wait! Most of us will get our first look around May 6 when Comet SWAN will appear very low in the eastern sky in Pisces about an hour to an hour 15 minutes before sunrise. You’ll need a wide-open view to the east (as close to the horizon as possible) and a pair of binoculars to spot it. The Great Square (see map above) will be your keystone. Find it and use its stars to “point” you to other stars near the comet. Then star-hop directly from those stars to the comet using binoculars. The glow of dawn will interfere but hopefully SWAN will be bright enough to stand out.

The comet’s orbit is steeply inclined to that of the planets. As it moves up and out of that plane we see it move sharply northward in the sky. Its direction of motion is reflected in its orbit. NASA / JPL-HORIZONS

The comet will continue to brighten as it move rapidly northward in the May dawn sky reaching a peak magnitude of 3.5 between May 15–23 while racing from Triangulum across Perseus. It reaches perihelion, when it’s closest to the sun, on May 27th at a distance of 40 million miles (64.3 million km). Bear in mind that while SWAN will be relatively bright it keeps stubbornly low northeastern sky at the start of dawn throughout the best part of its spring appearance. Binoculars are a must for the best views!

Be sure to check back here often. I’ll have regular updates on this exciting visitor!