A comet named for a spacecraft mission is currently rounding the sun and will soon appear at dawn. Comet NEOWISE (C/2020 F3) will pass nearest the sun on July 3 at a distance of 27.3 million miles (44 million km), nearly 9 million miles closer than Mercury. If it survives the solar onslaught skywatchers in the northern hemisphere will see the comet peep over the northeastern horizon at dawn starting about July 7. The unusual name comes from NASA’s Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) spacecraft which was used to discover the object back in March.
Estimates of how bright it will appear vary, but experts predict the comet will reach 3rd magnitude and possibly 2nd, equal to the brightness of the Big Dipper stars. Take this with a grain of a cometary ice. If NEOWISE stood high in a dark sky we’d have no problem spotting it with the naked eye, but it hovers near the horizon through mid-July, the same time it shines brightest.
Celestial objects near the horizon are much fainter than when seen overhead (think of the sun at sunrise vs. noon) because we’re looking through a greater thickness of air not to mention extra dust and humidity compared to seeing the same object overhead. Expect its low altitude to rob the comet of a magnitude or two. While it would still be a naked-eye object at say, magnitude 4, it would appear very faint.
My suggestion? Look at it in binoculars first then try to spot it without optical aid. Comet NEOWISE climbs higher through July but also distances itself from the sun which will cause it to slowly fade as the month rolls on. Of course we could be all wrong. The comet may surprise us and be brighter than predicted … or fainter. But all the indicators look good. It’s holding its own and will likely survive perihelion to make a nice appearance.
Two previous comets that graced the spring sky — ATLAS (C/2019 Y4) and SWAN (C/2020 F8) — were expected to be showstoppers, but both fizzled. ATLAS broke into pieces and turned into a “ghost.” SWAN likely disintegrated, too. Instead of rising in brightness when it cruised into the dawn sky in May, it slowly faded away.
To see Comet NEOWISE best, find a location with a view as close to the northern horizon as possible. A big field or a lake open in the direction would be perfect. And don’t forget binoculars. The brilliant star Capella in Auriga the charioteer will be your guide. Capella stands about 15°-20° high above the northeastern horizon around 3:30-4 a.m. at the start of dawn.
The comet will lie a fist and a half below the star about 5° (two fingers held together at arm’s length) above the horizon on Tuesday morning, July 7 and slowly climb through the week as it moves north and east. The morning moon will brighten the sky somewhat but wanes to half later that week and won’t present a problem after about July 10th.
I know getting up early requires a special effort, but if the comet puts on a show I’ll be there, and I hope you will, too. The timing is also ideal for looking for those strange noctilucent clouds we talked about in this recent blog. Watch for more information about NEOWISE and additional finder maps in the coming days. Clear skies!