Comet Iwamoto Wriggles Into The Evening Sky

On Feb. 2, Comet Iwamoto displayed a blue-green coma and a short, faint tail pointing northwest. The green color comes primarily from light given off by carbon when it’s excited by the sun’s ultraviolet light. Rolando Ligustri

What may be the brightest comet of the year is currently making a sweep across the evening sky. Before you get too excited, the object, named C/2018 Y1 Iwamoto, is only bright relative to the other comets we’re expecting this year. None of those are predicted to breach the naked-eye limit and it’s unlikely C/2018 Y1 will either. In truth, we’re talking another fuzzball similar to 46P/Wirtanen that passed by the Seven Sisters cluster last December. Just like that comet, this one is also visible in binoculars.

I like fuzzballs just fine and hope you will too. While we’re due for a comet to make us cower like the ones depicted in woodcuts from the Middle Ages, none are on the radar. Our last knock-your-socks-off cometary visitor was Hale-Bopp in 1997.

Japanese amateur Masayuki Iwamoto discovered the object on images taken December 18 last year. It has since brightened and moved from low in the morning sky to a more convenient altitude in the evening sky. I pulled into a dark, off-road spot Sunday night and found the comet in 10×50 binoculars in the constellation Virgo. It wasn’t particularly bright, but I had no trouble seeing it — a small, softly-glowing hazy spot about two-thirds the size of the full moon.

The comet shows up as a glowing patch (arrowed) in this tracked time exposure taken early on the morning of Feb. 4  I sketched in the “Y” or Cup of Virgo.  Bob King

Through a 10-inch telescope at 57x it was a giant blob with a faint aqua tinge like it had just stepped out of the Caribbean. The blob part is called a coma, and Iwamoto’s coma became denser as my gaze worked its way from edge to core. Other observers have reported seeing a short tail pointing to the northwest but as hard as I tried I couldn’t make it out.

C/2018 Y1 is currently magnitude 7, definitely within binocular range from a dark, non-light polluted sky. I suspect you’d see it in the outer suburbs of a medium-sized city as well, but it’s very diffuse, making the object a tough catch from a city.

Here’s the good news. Iwamoto passes closest to the sun today (Feb. 6) and will buzz just 28 million miles from the Earth on Feb. 12, growing a little brighter over the coming week. It also climbs quickly in altitude. Right now, you have to wait until 10:30-11 p.m. local time for it rise high enough for a good look. But by Sunday (Feb. 10), it’s already some 25° (2.5 “fists”) by 9 p.m. and just keeps getting higher after that.

(Updated) I’ve plotted the comet’s nightly position at 10:30 p.m. Central Time through Feb. 13. Depending on your time zone, it may vary from those positions a bit especially as the comet covers more ground later this week. Just interpolate between the dates to find it. Stars are shown to magnitude 6. The Greek letters are the names of stars the comet will pass near. If you’re not familiar with the Greek alphabet, click here. Stellarium with additions by the author

When near the Earth it will appear to move fast, covering 7.5° per day on Feb. 10-11. Even a small telescope will show the comet creeping along through the star field at the rate of nearly one-and-a-half “full moons” every 90 minutes. To find Comet Iwamoto use the map provided which shows the sky facing east-southeast around 10:30 p.m. Central Time. For the next few nights, the comet won’t be close to any bright stars but will soon cross into Leo the lion, a constellation with some easy sky-marks. From Feb. 9-12 you’ll find Iwamoto near or within the bright asterism called the Sickle of Leo, which also looks like a backwards question mark.

Catch the comet soon before the moon scuttles your dark skies. It’s a crescent now but waxing toward half (Feb. 12), so we have till about next Wednesday for good views unless you go out late after moonset. For more details including a very special conjunction the comet will have with a bright galaxy, please see my additional article and map in Sky and Telescope.

Crossing my fingers you’ll all be able to see this tuft of cosmic fluff.

9 Responses

  1. Norman Sanker

    One of the recent comets that I’ve been unable to find is 64P. I’ve been looking for months but it’s rarely been in a position for easy location and I just haven’t been able to catch it. But I hadn’t given up. Feb 6 had it reasonably near an unspectacular star that I should be able to identify. Problems: it would be almost directly overhead at the end of twilight (always awkward), and the weather had been cloudy for weeks. The weather cleared, which changed the problem from cloudy to cold–below freezing for the first time in a while. On Feb 6, I simply couldn’t do it, couldn’t motivate myself to face the cold. In the wee hours of the 7th, I reread your article on spanking new Comet Iwamoto, thought it should be well-placed and wondered if it was within backyard binocular range. No strong stellar pointers, but I had a vague idea where to search. I found an appropriate dark corner of the yard, scanned around where I figured it should be while my eyes adapted, shivered, scanned, rechecked my mental map, scanned–hey! Was that something? I stared, used averted vision, focused and refocused my old 9X35’s, and made a new mental note of the questionable blob’s location amid its star field. Back inside, out of the cold, to Heavens Above’s close-up Iwamoto chart
    –yes! Just as I had seen it. Still searching for 64P, but bagged Iwamoto.

    1. astrobob

      Hi Norman,
      I enjoyed reading about your comet adventure, and I’m happy you found Iwamoto — and in 9x35s no less! 64P never did get very bright. It was largish – which led to a brighter magnitude – but the comet was very diffuse, so it never struck me as particularly bright.

  2. Edward M Boll

    I have not even looked for 64 since December, now about magnitude 12. I have been still looking for, or at Wirtanen yet and pretty much given up on 38. I have yet to look for Iwamoto. I am a slow starter, and it has been stormy and cold here.

  3. Edward M Boll

    COBS has one report of seeing Iwamoto with the naked eye. The observer must have good eyes, magnitude stated at the time 6.4.

    1. astrobob

      Wow, that’s an amazing feat. No way would I have even attempted that this past Monday night. Hard for me to believe to be honest. Maybe my skies aren’t as good as I thought.

  4. Edward M Boll

    I read that the last time Iwamoto passed by was in 648 AD, an unrecorded event. No, I will not be around in this body of flesh, and I do not know how many generations will pass by until it’s next return in 3390.

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