April 20, 2014

Astro-Events: Of Comets and Meteor Showers.

Locating the Orionid radiant; (Photo/graphic by Author).

Early October saw one for the record books, as the obscure Draconid meteors put on a show for northern hemisphere observers topping a zenithal hourly rate of 338 ±15 per hour centered on October 8th, 20:04 UT. While not quite approaching storm levels, that’s the most impressive showing we’ve had from any meteor shower yet this century… the Draconids may produce once again in October 2018, and then we’ll have to wait ‘til the early 2030’s for the Leonids to ramp up again… incidentally, the Leonids, Draconids and the long defunct Andromedids are some of the only meteor showers that have historically approached storm intensity, usually informally defined as a ZHR ?1,000.

So, what’s a diehard meteor aficionado to do? Well, the good news is that a yearly standby is gearing up this week; the Orionid meteors are active from about the 17th until the 29th of October, centered on the morning of the 21st. Expect to see 20-40 meteors coming from a radiant just above and to the left of the bright star Betelgeuse in the shoulder of the constellation Orion. Also, this is one of the very few showers that are easily observable for those situated south of the equator, as well. Ever wonder why the southern hemisphere has a conspicuous lack of meteor shower radiants? We sense a PhD thesis in the works for anyone looking for ideas… The Orionids are material shed from that most famous of dirty icy snowballs, Halley’s Comet. We actually intersect the Halley debris stream twice during the course of the year, the other producing the springtime Eta Aquarids. An added bonus is that the waning crescent Moon is only 5 days until New and at 39% illumination on the morning of the 21st, visible during prime meteor observing time but not too overpowering light-wise… and don’t forget to report those meteors via Twitter to #Meteorwatch!

Note that there’s another reason to get up early this week; comet 45P Honda-Mrkos-Pajdusakova sits on the Leo-Sextans border in dawn skies at a magnitude +8 to +9, and infamous comet C/2010 X1 Elenin passes near the bright star Pollux. Comet Elenin passed the Earth at the non-threatening distance on 0.23 Astronomical Units (A.U.s) on October 16th, and was predicted to reach naked eye brightness around this time, but with its recent breakup, it’s anyone’s guess if this comet will be visible, even with binoculars. Be sure to check its most recent position against Heavens-Above before heading out on your comet-spotting quest!

The Astronomy Word(s) of the Week are Astronomical Unit. This is simply defined as the mean Earth-Sun distance, generally stated as 93,000,000 miles but more precisely set at 92,955,807.3 miles. This serves as a handy yardstick for measuring distances within our solar system; for example, the afore-mentioned 0.23 AU passage of comet Elenin works out to about 21,379,836 miles distant, about 89 times the distance to our Moon. For centuries, determining the Earth-Sun distance via the solar parallax was THE name of the astronomical game; once Kepler established the scale of the solar system, astronomers sought to garner precise parallax measurements during brief and infrequent transits of the planet Venus; modern day establishment of the astronomical unit was set by the International Astronomical Union in 1976 and utilizes reflection timings of radar transmissions off of the inner planets.

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