March 20, 2019

Astro-Event: On the Path of Comet Garradd.

We had great skies at our recent local Star Party this past weekend. Hot on the heels of the NecronomiCon, we zipped out to the relative darkness that is Starkey Park in Pasco county and set up for what turned out to be our third star party in 24 hours. Amidst Jupiter approaching opposition, a final ROSAT pass, and various deep sky wonders was a special treat; comet 2009 P1 Garradd lying at +7.9 magnitude on the Ophiuchus/Hercules border. Approaching perihelion on December 23rd at a distance of 1.551 Astronomical Units (A.U.s) from the Sun, this comet is still well placed in the evening skies as it glides northward through the constellation Hercules for the remainder of 2011. In fact, comet Garradd will reach a northernmost declination of +70.7 degrees on March 11th of next year, shortly after its closest passage to Earth of 1.27 A.U.s on March 5th. Garradd also has a high inclination relative to the ecliptic of 106.2° degrees. This all means the folks in mid-northern latitudes should be able to track Garradd right through perihelion as an evening object low to the northwest through the end of 2011 and then as a morning object in the northeast as a morning object in early 2012. Chances are pretty good that Garradd should break naked eye visibility from a dark sky site; it looked very much like a fuzzy unresolved globular cluster to me thru my 8” SCT, but some folks mentioned what they thought was a short, spikey tail. Keep an eye on Garradd on February 3rd 2012 as it passes within 1/2° of the globular cluster M92 (photo op!)… Discovered on August 13th 2009 by Australian astronomer Gordon J. Garradd during the Siding Spring survey for Near Earth Objects, Garradd has proven and will continue to be a great binocular comet!

Path of Comet Garradd through early 2012; (Created by Author in Starry Night & Paint).

The Astronomy term of the Week is hyperbolic orbit. Note that comet Garradd’s eccentricity is listed as 1.001011… this means it’s on an open trajectory, tracing out a path known as a hyperbola. A comet on a hyperbolic orbit is perhaps a first time visitor to the inner solar system from the distant Oort Cloud, on a path to possibly getting ejected from the solar system out to interstellar space. Comet Garradd belongs to a class of comets that walk the fine line between a closed and open orbit; its current path suggests a previous orbit of 120,000 years, and after this passage of the inner solar system, its orbit will be +600,00 years, if it returns at all. In the case of comet Garradd, perihelion is occurring near the average distance of Mars from the Sun; had the large comet been approaching the Sun closer or had the Earth been six months or so earlier or later in its orbit, we would have been on track for a Great Comet… Astronomers get some inkling that a comet may be large and intrinsically bright once the initial distance is measured and the apparent brightness is compared. In the case of comet Garradd, discovery magnitude was around +17.5 at around 8 A.U.s distant, just inside the orbit of Saturn. This will be the only look we get at this visitor to the inner solar system during our current epoch…still, there’s lots more out there!


  1. Harry Garcia says:

    can you post something on comet 2p/encke?

  2. David Dickinson says:

    Hmmm… Comet 2P/Encke reaches favorable visibility next March; will probably be writing about it either here or on Universe Today by then, sure.

    Dave Dickinson

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