December 21, 2014

Astro-Event: See Mercury at its Best.

Looking east the morning of December 3rd an hour before dawn.

(Created by the Author in Starry Night).

By now, you’ve no doubt been thrilled by last week’s dramatic passage of Venus and Saturn in the dawn sky. Well, as the old Late-night TV ad cliché says, “But wait, there’s more…”

Fresh off of inferior conjunct and a near transit of the Sun that missed the solar limb by less than 8’ minutes on November 17th, the planet Mercury joins the pair for a stunning gathering.

This will be Mercury’s best dawn (westerly) apparition for northern hemisphere observers in 2012. Use brilliant Venus shining at magnitude -3.9 just above speedy Mercury to find the elusive -0.4 magnitude world looking low to the east about an hour before local sunrise. Mercury reaches its greatest elongation for this apparition at 20.6° degrees from the Sun at 06:00 UTC/ 01:00 EDT on December 5th, shy of its 27.8° greatest possible maximum. Remember, Mercury has a very elliptical orbit and thus elongations can vary from 27.8° degrees (near-aphelion, as last/next will happen on April 18th, 2012 & March 31st, 2013) to 17.9° degrees, (near-perihelion, which will last/next happen on September 19th, 2010 & September 28th, 2016). All three worlds of Mercury, Venus and Saturn will form a line about 12° degrees of arc long on the morning of December 3rd, a sight not to be missed! The waning crescent Moon will even join pairing on mornings from December 9th through the 12th, and will actually occult (or pass in front of) the bright star Spica for the southern tip of South America & Antarctica on December 9th and Mercury on the 12th, also from Antarctica… the rest of us get to see a close pass.

Jupiter reaches opposition on December 2nd. This year’s opposition occurs at 01:00 UTC (On the 3rd)/ 20:00 EDT and will see the planet setting in the west as you’re viewing planets in the dawn. Jupiter will be entering the evening skies in December and will present a disk 49” across. 2012-2014 sees the orbits of the Jovian moons of Io, Europa, Ganymede and Callisto nearly edge-on from our Earthly vantage point, and a series of mutual eclipses are currently underway. Also, keep an eye on the planet’s “Great Red Spot,” which has appeared a bit faded as of late. Jupiter is currently in the constellation Taurus and will next reach opposition on January 5th, 2014.

Also, keep an eye out for a curious meteor shower on those early morning vigils. The Andromedids peaked with an estimated and respectable Zenithal Hourly Rate of 50 in 2011 centered on December 5th at 9:00-12:00 UTC. This was once an annual meteor shower in the 19th century, but had trickled off into near-nonexistence in the 20th. Could the Andromedids be making a comeback? The Moon will be at a 63% illuminated waning gibbous phase the morning of the 5th, and thus will be a factor in how many meteors may be seen. The modern day Andromedids are a minor shower with a broad peak running from mid-September to early December, but with the renewed activity seen last year it’s worth watching out for this obscure shower. Did you know? The very first picture of a meteor was an Andromedid, taken by Ladislaus Weinek in 1885! The Andromedids have a relatively high northern radiant of +37° degrees located in the constellation Andromeda near Gamma Andromedae. The Andromedids produced outbursts of thousands per hour in 1872 and 1885, and we may intersect some active streams again in 2018 & 2023. The source comet for the Andromedids is comet 3D/Biela. Be vigilant for this shower in the early morning hours of December that may be making a comeback!

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