April 24, 2019

AstroEvent: The Tail(s) of Two Comets.

As the Moon begins its inexorable wane after passing Full phase this weekend, we’d like to turn you attention to two decent comets currently gracing opposing hemispheres.

First up is the tongue twisting comet 45P/Honda-Mrkos-Pajdušáková. This Internet search-defying comet currently shines at about magnitude +8 and is actually a circum-polar object for New Zealand viewers this month. It will pass just 0.06 Astronomical Units from Earth (about 5.5 million miles, still over 22 times the Earth-Moon distance) on the 16th and passes near the Southern Magellanic Cloud just before on the 13th, and through the Large Magellanic Cloud as a fine photographic target on the 15th! US observers won’t have much of a chance at getting a peak at 45P/Honda-Mrkos-Pajdušáková as it moves northward through Pyxis, Hydra, and Leo through the end of the month, becoming lost in the sun’s glare. Too bad, as the comet’s very name would drive reporters nuttier than an Icelandic volcano (perhaps that’s why it’s remained so obscure?)   Honda-Mrkos-Pajdušáková reaches a perihelion of 0.52 AU on September 28th 2011.

Path of Comet Garradd through September 1st; (Created by Author in Starry Night).

For us northern hemisphere-based observers, the big treat this month has been comet C/2009 P1 Garradd. Discovered by G.J. Garradd at Siding Spring Observatory in 2009, comet Garradd just passed a maximum solar elongation of 149 degrees on August 8th of this year and made a very photogenic pass of the M15 cluster in early August. Interestingly, the comet will also make very close (<30’) passes of the bright stars Gamma Delphini (August 14th) and Zeta Sagittae (August 28th) as it heads towards a perihelion of 1.6 A.U. on December 23rd. August 26th also finds comet Garradd transiting the globular cluster M71 in the constellation Sagitta, and pairing with the Coat-Hangar asterism on September 2nd. We’ve been tracking comet Garradd, and it is currently an easy +8 magnitude binocular object high in the early morning sky, just southwest of the zenith in Pegasus.  Expect it to reach magnitude +6 Through March 2012 as it too goes circumpolar for northern viewers reaching a declination of +70.7 degrees on March 11th, shortly after passing within 1.27 AU of the Earth on March 5th 2012. And of course, in other cometary news, NON-EARTH impacting comet C/2010 X1 Elenin (no, we’re NOT in cahoots with the government to cover things up, as our destitute pro bono blogging lifestyle demonstrates!) may put on a good Fall showing, and C/2011 L4 PANSTARRS may be the comet to watch in 2013… watch this space for all the cometary action and updates!

The astro-word(s) of the week is Short Period Comet. This is defined as a comet who has an orbital period of less than 200 years and the path of which is very precisely known. Comet 2/P Encke is well-known example of this class with a 3.3 year orbit, as is comet Halley with a 75.3 orbit. This year’s current crop of Oort Cloud transients is a good study in contrasts; for example, comet 45P/Honda-Mrkos-Pajdušáková is a short period comet with a 5.25 year orbital period, while Comet Garradd is on its first passage of the inner solar system on a hyperbolic orbit that may see its ejection. Short period comets evolve as they enter resonances with inner worlds whose path they cross. Conversely, first time visitors to the inner solar system have the potential to become Great Comets which often come (silently) screaming in unannounced from the deep space regions of the Oort Cloud. These visitors stand about a 40% chance of having their orbit altered by the massive planet Jupiter. For example, Hale-Bopp originally had a 4,200 year orbit, but on its 1997 passage, its orbit was shortened down to about 2,533 years. It’s always possible that a comet like Hale-Bopp might strike a “sweet spot” resonance in the far off future to become a crowd pleaser like Halley’s, but predicting orbital resonances into the remote future can be a fiendish affair!

Trackbacks

  1. [...] Interestingly, the comet will also make very close (<30’) passes of the bright stars Gamma Delphini (August 14th) and Zeta Sagittae (August 28th) as it heads towards a perihelion of 1.6 A.U. on December 23rd. August 26th also finds comet Garraddtransiting the globular cluster M71 in the constellation Sagitta, and pairing with the Coat-Hangar asterism on September 2nd. We’ve been tracking comet Garradd, and it is currently an easy +8 magnitude binocular object high in the early morning sky, just southwest of the zenith in Pegasus.  Expect it to reach magnitude +6 Through March 2012 as it too goes circumpolar for northern viewers reaching a declination of +70.7 degrees on March 11th, shortly after passing within 1.27 AU of the Earth on March 5th 2012. (AstroGuyz) [...]

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