.by Anura Guruge
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>> — June 10, 2013.
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Yes, Comet ISON, C/2012 S1, is still on the way, but still a long ways out (as I pointed out 10 days ago). I am banking on it and have my hopes high. A blazing comet in the sky, à la Hale-Bopp [C/1995 O1] in 1997, is always inspirational and so uplifting. Just getting a glimpse of C/2011 L4 (Pan-STARRS), through binoculars, as it sped away from us, in April was a thrill.
If ISON survives perihelion it will flyby Earth on Boxing Day, i.e., Thursday, December 26, 2013, 39.9 million miles away from us. Contrary to the deluded this is by no stretch of the imagination a close call. That is quite a separation. Mars, every once in awhile, comes closer to Earth than that.
But, on July 1, 1770, when D/1770 L1 (sometimes referred to Lexell’s comet, though he was not the discoverer) passed within 0.0151 AU, i.e., 1.4 million miles of the Earth. This per the International Astronomical Union (IAU), the ultimate authority on such matters, is the closest documented cometary encounter.
So D/1770 L1 was nearly 29 times closer — and even it did no harm, because even 1.4 million miles is a ‘safe’ separation.
On February 4, 2011, the tiny asteroid 2011 CQ1 which came within 3,400 miles of Earth – just hours after it had been espied by the Catalina Sky Survey on February 4, 2011.
D/1770 L1 was discovered on June 14, 1770 by Charles Messier [1730 to 1817], a French astronomer of note, who had already discovered five earlier comets, and would go onto discover seven more. So this ‘near-Earth’ comet was only spotted two weeks prior to its ‘fairly close’ flyby.
The identification with ‘Lexell’ has to do with a bestriding polymath of the time, Swedish-born Russian Anders Johan Lexell [1740 to 1784] who using a new groundbreaking technique quickly calculated the orbital parameters of the new comet based on Messier’s observational data. It perihelioned on August 14, 1770 at 0.7 AU. It has since been lost as denoted by the ‘D/’.
The two dots are Earth, in green below, and the comet, in blue. That is adjacent. Click to access NASA/JPL orbital plot tool. You will need working Java (and a cup of coffe is always nice too).