Comet SWAN: How and When to Watch Green Glowing Cosmic Snowball Fly Past Earth

Comet SWAN, otherwise known as C/2020 F8, is currently located more than 52 million miles away from our planet as it makes its closest approach to Earth Tuesday in its orbit around the sun.

Those in the Southern Hemisphere will have the best views of the comet for now, but the cosmic snowball is moving from southern to northern skies.

For those in the United States, the comet which has a greenish glow when seen through binoculars and telescopes, is faintly visible in dark skies only from the far southern portions of the country, such as Hawaii and Florida, as it moves through the constellation Pisces, according to amateur astronomer Bob King writing for the Duluth News Tribune.

However, the comet will be difficult to spot for most Americans because it only appears very low above the eastern horizon during the morning twilight, just before sunrise. Because the comet gets higher in the sky as dawn breaks, those in mid-latitudes in the Northern Hemisphere likely may have trouble seeing it in dark sky, rendering the object invisible.

"The comet will never be particularly well placed for most of us in the United States, but observers in southern Florida and Hawaii could get some decent views from east-facing coasts," Rick Fienberg, a spokesperson for the American Astronomical Society, told Newsweek. "For those in the southern parts of the U.S., the comet will peek above the northeastern horizon at dawn in mid to late May."

The excited wagging of Comet SWAN's ion tail. Photos by Gerald Rhemann, taken over the first 5 days in May.

— Corey S. Powell (@coreyspowell) May 9, 2020

With an observed magnitude of 5.4 at the time of writing, the comet is, theoretically, just about visible to the naked eye for those in the right latitudes.

However, because it is low in the sky, the comet can be difficult to see unaided, even on a clear night, according to King, who recommends using binoculars and choosing a site that has wide-open vistas down to the east-northeast horizon.

"While this fuzzy visitor is officially naked-eye brightness it will appear fainter because it's low in the sky," King wrote. "When we look along the horizontal we see through the thickest, dustiest part of the atmosphere which absorbs light and makes otherwise bright objects, even the moon, appear fainter compared to when they're higher up."

Astronomers think that the comet is expected to brighten, perhaps reaching up to around magnitude 3 towards the latter part of May. However the behavior of comets is notoriously unpredictable and it is possible that the object could break apart as it approaches the sun.

Stock image: Artist's illustration of a comet. iStock

Even if does brighten, the comet will still be low in the north-eastern sky before dawn, meaning it may not be discernible in the growing twilight, except through binoculars or a telescope, according to Fienberg.

From about May 22/23 to mid-June, the comet will also be visible in the evenings at the very end of dusk as it crosses from the constellations Perseus into Auriga. But again it will be tricky to see due to being very low in the sky above the north-northwest horizon, so binoculars are recommended, Sky & Telescope magazine reported. If you do manage to spot the comet, try lowering the glass to see if you can see it with the naked eye.

The comet, which was officially described in in mid-April by amateur astronomer Michael Mattiazzo, will make its closest approach to the sun on May 27 when it will be around 40 million miles from our star.

According to NASA, comets are "cosmic snowballs" composed of frozen gases, dust and rock that orbit the sun, which produce long tails as the approach our star.