Around 8 p.m. CDT Weds. July 22 Comet NEOWISE makes its closest approach to the Earth at a distance of 64.3 million miles (103.5 million km). That’s about two-thirds the distance between the Earth and sun, so not very close. Normally you’d think the comet would be brightest now but instead the it’s been slowly fading since early July. Why? NEOWISE sailed nearest the sun on July 3 and has been receding from it ever since. Since the comet shines by reflected sunlight, the farther it gets from the sun the fainter it becomes. Still, it doesn’t hurt that NEOWISE has been closing in on Earth for the past few weeks — that’s certainly helped to slow its fading.
After today it heads back to the Oort Cloud not to be seen again in these parts for another 6,800 years. NEOWISE is currently about magnitude 3.5, a magnitude and a half or about four times fainter than it was a week ago. Yet the comet still hangs in there. While not as obvious in twilight as it once was, it’s still easy to see at nightfall in a dark sky with a long, delicate dust tail.
A pair of binoculars remains the instrument of choice when it comes to getting the best look at NEOWISE. That’s especially true now that the waxing moon has entered the picture. I’m often asked how long we’ll see the comet. It should remain visible from a dark sky without optical aid up until about August 1 — theoretically. But light from the half-moon will make this a challenge starting July 27-28. For the best views of the comet go out now through July 26.
From August 1-15 binoculars will still show the comet, but the tail will become increasingly faint and difficult to make out. If predictions hold true you’ll need a modest-sized telescope to pick up the comet in late August and a considerably larger one by mid-September. Throughout, NEOWISE moves southward, passing from Ursa Major into Coma Berenices (Queen Berenice’s hair) on July 29th. After a brief stay in Boötes in early August it arrives in Virgo on the August 15th. The comet’s altitude remains roughly the same throughout its evening appearance — about 25° high at nightfall from 40° N latitude.
Next week brings good news for Southern Hemisphere skywatchers when we finally get to share our fuzzy friend with comet lovers on the other end of the Earth. If you’re one of them, watch for NEOWISE low in the western sky toward the end of evening twilight. For northerners the comet is still an easy naked-eye object from dark skies, looking like a smoky streak with a broad, faint tail that extends upward toward the bowl of the Big Dipper. From the city and suburbs the comet is faint and best viewed in binoculars.