A visitor from outer space

Seen at 5:00 in the morning, July 9, 2020, C/2020 F3 rises over calm Lake Erie waters and predawn colors. Photo by James Guilford.

The talk amongst stargazers this summer has been the apparition of C/2020 F3 NEOWISE in Northern Hemisphere skies. Previously one comet had caused excitement over its potential showing but it broke up as it approached the Sun. Another fizzled and faded from view. But C/2020 F3 survived its July 3 close approach to the sun (perihelion) and emerged bigger and brighter than expected.

The comet’s brightness is due to its large nucleus — the head of the comet — which is the source of frozen gas and dust that produces the visible tail or coma. “From its infrared signature, we can tell that [the nucleus] is about 5 kilometers across,” said Joseph Masiero, NEOWISE deputy principal investigator at NASA’s Jet Propulsion Laboratory.

C/2020 F3 was discovered in infrared images captured by NASA’s NEOWISE spacecraft in March 2020. The object was assigned the unromantic designation of C/2020 F3 with the spacecraft’s name as discoverer.

Comet C/2020 F3 with normal exposure (top), then brightened in processing to bring out fuller extent of its dust trail (lower image). Photo by James Guilford.

Falling in from the outer solar system, then diving perilously close to the Sun gave our comet a boost in speed and increased its orbital period from about 4,500 years to about 6,800 years — a long time to wait for its return.

Until recently C/2020 F3 put in its appearances only in the predawn hours, rising a little after 3:30 AM and fading into the brightening sky a bit past 5:00 AM. It was also rising to only about 10º above the horizon placing it, much of the time, in the realm of morning clouds, mists, haze, and general murk.

But it’s not over.

While at the time of this writing C/2020 F3 continues to be viewable in the wee hours before dawn in the northeastern sky, sinking lower with each morning, it is now also showing in the post-sunset twilight. It’s still only becoming visible around 14º to 10º above the north-northwestern horizon as it sinks toward the horizon following the Sun. The comet sets around 12:30 AM.

July’s evening sky offers more convenient viewing hours for C/2020 F3. Credit: SkySafari

Evenings, for the next couple of weeks and possibly into August, go comet hunting! Depending upon whether the sky is clear of obstructions, clouds, and haze, skywatchers may be able to see the comet with unaided eye. Good binoculars will help in finding it and will give seekers a better view. The comet will be very low to the horizon so an elevated location will aid in viewing. Use binoculars to look west and then past northwest in the deepening twilight, scanning slowly and just above the horizon. The comet will appear as a vertical streak with a bright dot at the lower end, as in the picture at the top of this page. It may not be spectacular but how many comets does one see in their lifetime?

Our outbound visitor from outer space makes its closest pass by Earth on July 23 when it will be 103.7 million kilometers — about 64 million miles — away returning in roughly 7,000 years.