Solar System Observing

I once asked David Eicher, the editor of Astronomy magazine, what it would take to rekindle widespread interest in amateur astronomy in a time of constant technological distraction, and when truly dark skies are growing rare. His answer was simple: a brilliant naked-eye comet with a spectacular tail visible near the zenith for a year. That would get people looking skyward again for sure.

Comet C/2020 F3 (NEOWISE) was not that comet. Nor was it a ‘Great Comet’, in astronomical terms. But it was a good one, and it offered serious stargazers and the untutored alike a chance to see something remarkably beautiful and unexpected, and it gave us a short break from the onslaught of unsettling news this year.

Like many impressive comets, NEOWISE arrived as a surprise. It was discovered on March 27, 2020 by the near-Earth-object (NEO) mission of the Wide-field Infrared Survey Explorer (WISE) space telescope, when it was already in the inner solar system on its way to a close approach to the Sun on July 3. There was some hope that, if it survived its encounter with the Sun at a distance of 42 million kilometers, it might become respectably bright. NEOWISE disappeared in the Sun’s glare at 7^th magnitude and came out at 3^rd magnitude, and all in one piece, late in the first week of July. As it moved away from the Sun and closer to the Earth, the apparent brightness increased to about first magnitude. A bright naked-eye comet arrived at last, the first in the northern-hemisphere since Hale-Bopp in 1997 (southern-hemisphere observers enjoyed the spectacular Comet McNaught in early 2007).

By the time I laid eyes on NEOWISE, on July 13, it was an easy naked-eye object even in my relatively bright urban sky about ten degrees above the northwestern horizon. The comet from my northerly location was circumpolar, which means it never set below the horizon, and it moved from west to east since it was below the celestial pole. Even at my relatively favorable urban observing site, there were surprisingly just two other observers, both local photographers doing their business with long lenses and serious cameras. We were treated to a brief display of noctilucent clouds followed by faint aurora borealis which, together with the comet, made for some spectacular image making. Given the length of its tail, which spanned at least ten degrees, the comet looked better in binoculars than a small telescope. It was a very easy object to photograph so I snapped away with a medium telephoto lens and a mirrorless Nikon to get a few keepsake images. Since sleep for me is a rare and precious commodity, I packed it in after an hour while the comet swung lower over the northern horizon.

On July 24, when I got my next look at NEOWISE, there were about a hundred observers at the same spot thanks to breathless news reports and a blizzard of images on social media. By then, however, the comet had dimmed considerably and was only visible in binoculars. Some in the crowd of stargazers-for-a-night were only mildly disappointed, but they spoke excitedly among themselves of nights long ago spent stargazing under dark sky. I stood next to 40-something fellow, possible a schoolteacher, who recited to me some basic facts about the comet and how to see faint celestial objects using averted vision. I nodded judiciously and thanked him, then moved on to helping an older woman find the comet with her spotting scope. She was thrilled. Yes, I thought, Eicher was right. If this comet could just hold on for a few more months, there’d be a lot more stargazers in the world.

 

 

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A post shared by Rutger Bus (@rutgerbus) on Jul 24, 2020 at 1:15pm PDT

The images of Comet NEOWISE continue to pour in: this may well be the most photographed comet in history. And for good reason: it’s a remarkably photogenic comet with a lime-green lollipop coma of excited cyanogen gas, a long arcing yellow-white dust tail, and a blue arrow-straight ion tail pushed back by the charged particles of the solar wind. It looked like a little-brother of the magnificent Comet Hale-Bopp, a comet so bright it remained a naked-eye object for an astonishing 18 months through 1996-1997. Hale-Bopp likely retains the record for the most observed comet in history, however. Estimates suggest nearly 70% of North Americans saw the comet at least once.

Thousands of images of NEOWISE have been published. The embedded Instagram image above, made by the Dutch photographer Rutger Bus, is in my view one of the very best.

Now, NEOWISE is on its way back to the outer solar system. As it moves away from the Sun through July and into August, it will dim quickly and slow on its way to aphelion about 3,000 years from now some 300 astronomical units from the Sun. On July 27, I took one last look at the comet on a night of Milky Way imaging in dark and clear sky. It was still easy to see under the Big Dipper as a ghostly silver-white wedge tipped towards the northwestern horizon. In the wide-field image above, the comet almost looks a little forlorn as it moves away under the Big Dipper, over a hill and far away on its way to the outer solar system, shepherded by the gaze of a dwindling number of stargazers and subject to the merciless laws of celestial mechanics. Thanks Comet NEOWISE, for brightening our skies a little, and reminding us of the pleasures of looking up from our troubles from time to time.