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Thread: Comet Wirtanen

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    Comet Wirtanen

    In December, Comet 46P Wirtanen will pass seven million miles from the Earth. Closer than Hyakutaki in 1996.
    http://wirtanen.astro.umd.edu/46P/index.shtml

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    Seems like a while since we've had a good, naked eye comet, at least in the Northern hemisphere. I guess time will tell with this one.
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    This is going to interesting, a christmas star! and at that, the original target of Rosetta!
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    Just looked at Witanen with a C-8, 40mm eyepiece. Coma is large and so diffuse it was hard to tell exactly where the coma ended and the background sky began. Nice sight through 15x70 binoculars.

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    Quote Originally Posted by Superluminal View Post
    In December, Comet 46P Wirtanen will pass seven million miles from the Earth. Closer than Hyakutaki in 1996.
    http://wirtanen.astro.umd.edu/46P/index.shtml
    Thanks for the head's-up!

    Sky & Telescope has a new article about it and a plot. The brightest magnitude ranges from 8 to almost 3, depending on who is estimating. Perhaps we should have a contest?

    It should be easy to find since the Belt of Orion almost points directly at it on or about the 16th.
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by George View Post
    Thanks for the head's-up!

    Sky & Telescope has a new article about it and a plot. The brightest magnitude ranges from 8 to almost 3, depending on who is estimating. Perhaps we should have a contest?

    It should be easy to find since the Belt of Orion almost points directly at it on or about the 16th.
    That's really useful and yes, given the proximity to Orion and The Pleiades, even I'll be able to find it.
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    Quote Originally Posted by George View Post
    Thanks for the head's-up!

    Sky & Telescope has a new article about it and a plot. The brightest magnitude ranges from 8 to almost 3, depending on who is estimating. Perhaps we should have a contest?

    It should be easy to find since the Belt of Orion almost points directly at it on or about the 16th.
    [Added: It looks like it will be at the meridian just before midnight (CDT) on the 15th & 16th, high altitude, 7.2 million miles or so.] [Ok, I thought I was adding it to my prior post. ]
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by Swift View Post
    That's really useful and yes, given the proximity to Orion and The Pleiades, even I'll be able to find it.
    Yep, that was the first thing I liked about it.
    We know time flies, we just can't see its wings.

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    Thanks for the head's-up!
    Double That! It's News to me, From Georges S&T source : "In April 1972 and again in February 1984, the comet made close approaches to Jupiter, ultimately shortening its orbital period from 6.7 to 5.5 years and pushing the comet’s perihelion distance some 82 million kilometers (51 million miles) closer to the Sun, to a point just over 8 million kilometers (5 million miles) outside of Earth’s orbit."

    It's a pretty green color from the pic at the site. So now, this comet has very recently been flung much closer to the sun in its new orbit, and at the same time of it closest approach to the sun it just so happens to be at its closest approach to the Earth, roughly Dec 16th?. Nice coinciding. The 1sr Qtr moon is on Dec 15th, be lucky if it's not overcast/raining.

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    Cool

    George has suggested that I provide a link to my two Comet 46P Wirtanen charts and ephemeris: https://www.CurtRenz.com/comets.html

    Just now I updated them for the latest magnitude parameters provided by JPL. The orbital elements remain those of the highly accurate Solex astronomical numerical integration program.

    On my comets webpage is similar information for 38P Stephan-Oterma and C/2018 V1 Machholz.
    For astronomical graphics and data visit
    https://www.CurtRenz.com/astronomy.html

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    Thanks Centaur!
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    Even under the Bortle Class 6 to 7 skies of Fresno, CA, I was able (barely) to spot Comet 46P at about 10:00 p.m. tonight with handheld 15x70 binoculars. Fortunately, it rained over the past couple days and the seeing and transparency were both much better than average.

    The comet was right where it was supposed to be, which I confirmed with the star field shown in a detailed finder chart from SkyTools 3. The comet is bright (~m3.4), but so large (~1.5) that its surface brightness is low and that's a killer under my suburban skies. The core was slightly brighter than the rest of the comet, which made it easier to spot.

    Next Saturday, if conditions permit, I will be observing with my 11" SCT at 6,500 ft in Kings Canyon National Park and Comet 46P is in my observing plan.

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    3.4 mag.?
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    There's a big difference between the magnitude of _all_ the comet's light, from the central bright region as well as from the diffuse areas and tail, and the magnitude of the compact, bright spot at its center.

    Ten days ago, I took some CCD images of the comet under bright, moonlit skies. In the pictures, it was easy to see the central bright spot; and that spot was clearly not a normal star, as it was twice or three times as broad as a typical stellar image. However, that central bright region of only a few arcseconds in diameter was also relatively faint: magnitude 11 or so in V-band.

    What the CCD images didn't (easily) show was the immense amount of low-level light spread out around this central spot. The diffuse regions have low surface brightness, making them blend into the general sky light. However, that diffuse light covers so much area that it may contain more than 100 times as much light as the compact source at the center.

    So, when you read that the comet has reached magnitude 3, or 4, that's the total light, which your eye is not likely to register. Through a telescope or binoculars, it will appear much fainter.

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    Quote Originally Posted by StupendousMan View Post
    There's a big difference between the magnitude of _all_ the comet's light, from the central bright region as well as from the diffuse areas and tail, and the magnitude of the compact, bright spot at its center.

    Ten days ago, I took some CCD images of the comet under bright, moonlit skies. In the pictures, it was easy to see the central bright spot; and that spot was clearly not a normal star, as it was twice or three times as broad as a typical stellar image. However, that central bright region of only a few arcseconds in diameter was also relatively faint: magnitude 11 or so in V-band.

    What the CCD images didn't (easily) show was the immense amount of low-level light spread out around this central spot. The diffuse regions have low surface brightness, making them blend into the general sky light. However, that diffuse light covers so much area that it may contain more than 100 times as much light as the compact source at the center.

    So, when you read that the comet has reached magnitude 3, or 4, that's the total light, which your eye is not likely to register. Through a telescope or binoculars, it will appear much fainter.
    Yes, that's very helpful for those who may not be aware of the differences. [It's interesting to me that no telescope (visual use) can increase surface brightness beyond that seen by the eye of an extended objected, though magnification does help a little bit.]

    The predicted range of maximum apparent magnitude seems to be from 8 to 3, or am I wrong? I assume these are the combined apparent magnitude (nucleus, coma and tail(?)). By the 16th, it will be 1.6x closer than it was on Dec. 1st, thus it will be more than 2.5x brighter (~ 1 mag. brighter) assuming no other changes and ignoring phase angle differences, if any. [The brightness will be just a little more than the square of the distance ratio.] Hopefully it heats up enough to make a better show than this.

    So, does this suggest it could be as bright as a 2 mag.?
    Last edited by George; 2018-Dec-02 at 06:40 PM.
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    It should be interesting to see the imagery produced on December 15 and 16 when Wirtanen is within a 10 degree FOV of the Pleiades. I might even try some afocal camera work...even I can find a comet when it's near something bright and easily found!

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    Just hoping that the skies will clear, here in Austria, and I will kindly borrow that location figure if you don't mind.
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    Maybe if we're lucky, we'll get a major out burst around closest approach to Earth. Like Comet Holmes did a few years ago. But according to the UofM http://wirtanen.astro.umd.edu/46P/46P_properties.shtml There have only been two outbursts observed, 2002 & 2008, not very likely.

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    Quote Originally Posted by tusenfem View Post
    Just hoping that the skies will clear, here in Austria, and I will kindly borrow that location figure if you don't mind.
    The image is from the Heavens Above site and represents 21:30 on December 16 from my Atlanta (GMT -5) location. So the actual position of the comet will vary a bit for central
    Europe but not enough to matter, I would think.


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    Quote Originally Posted by schlaugh View Post
    The image is from the Heavens Above site and represents 21:30 on December 16 from my Atlanta (GMT -5) location. So the actual position of the comet will vary a bit for central
    Europe but not enough to matter, I would think.


    Sent from my iPhone using Tapatalk Pro
    yeah, in the end i decided to to go to the source for an austria figure ��
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    Last night at Big Stump we had better than average conditions for December. I rate both seeing and transparency at 4/5, with transparency dropping to 3/5 around 10 p.m.

    I arrived around 3:30 p.m. to set up my 11" SCT (Celestron CPC-1100 HD) and eat an early dinner. Two other club members arrived soon after (another 11" SCT and an 8" dob), and a third arrived well after dark (20" dob). At about 5:00 p.m., the temperature was 40F. When I left at about 11:15 p.m., it was right at 32F. There was snow all around the parking lot, but the parking lot itself was clear and the restrooms were working again (throughout the summer and fall, the restrooms were closed and the Park Service had set up a dozen porta-potties in the parking lot…thank goodness for small victories).

    In the early evening, sky glow along the horizon from cities in the San Joaquin Valley down below was very evident, but an inversion layer over and incipient fog in the valley began forming around 8:00 p.m. and the horizon turned dark. I hit a little fog on the drive home, but it wasn't bad.

    I first looked at the comet at 7:15 p.m. The nucleus was very bright and the coma extended well beyond the 1 field of view of my 41-mm eyepiece. In the 8" dob with a 35-mm eyepiece (2 field of view), I could see not only the entire coma, but a bit of the tail. I looked at the comet several more times last night, with the best view coming at 9:00 p.m. (higher in the sky and the sky being slightly darker). My last view (10:15 p.m.) was the worst due to the decrease in transparency: the nucleus was still just as bright, but the coma was fainter.

    BTW, M31 was easily seen naked eye, but I couldn't see M33 naked eye (something I have done before up there). The younger eyes in our group were able to see the comet nucleus naked eye, but I couldn't.
    Last edited by skysurfer5cva; 2018-Dec-10 at 10:05 PM.

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    The comet is still hanging there. A challenging object to see with the full moon sharing the same sky. When it passed closest to the Earth, did Arecibo manage to image the nucleus, or was it too far away for radar?

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    Quote Originally Posted by Superluminal View Post
    The comet is still hanging there. A challenging object to see with the full moon sharing the same sky. When it passed closest to the Earth, did Arecibo manage to image the nucleus, or was it too far away for radar?
    Yes, the two first hits on arecebo + wirtanen are:
    http://www.naic.edu/~pradar/
    https://phys.org/news/2018-12-captur...ges-comet.html

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    The comet is receding and dimming. The UMD Comet Wirtanen page has links to several articles about the comet.
    http://wirtanen.astro.umd.edu/46P/46P_press.shtml

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    I saw it easily with both 7x and 15x 50mm binoculars late Wednesday night, in a clear sky with the skyglow a little over 1 magnitude brighter than a pristine sky. I was about 15 miles west-southwest of Dulles Airport and 38 miles from Washington DC.

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