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The Sky This Week, 2010 November 23 - 30

A Blue Moon Primer, Thanksgiving and the Sky.

Jupiter, with outbreak spot and plume,
Imaged from Alexandria, VA on 2010 NOV 20, 23:55 UT

The Moon wanes in the morning sky this week, with Last Quarter occurring on the 28th at 3:36 pm Eastern Standard Time. Luna begins the week rising in the late evening among the stars of Gemini. On the morning of the 28th she may be found five degrees due south of the bright star Regulus in the constellation of Leo, the Lion. By the end of the month she is closing in on Saturn, the bright star Spica, and Venus as a waning crescent in the gathering morning twilight.

There’s been considerable confusion over the proper name to call last week’s Full Moon. Old folklore, both Native American and European, bestows names on each month’s Full Moon which is usually indicative of the time of year. In most years each season will have three Full Moons, but since a lunar year is about 11 days shorter than a solar year once in awhile an "extra" Full Moon occurs to gum up the works. This extra Moon became known as a "Blue Moon", but the real question became how to define it. Most of us have been told that a Blue Moon is the second Full Moon to occur in a given calendar month. The next time this occurs will be in August, 2012. However, a more subtle and folklore-oriented description is now being accepted as the "true" definition of the term which has more to do with the seasons than with calendars. Each year has four seasons, and each season generally has three Full Moons. Once every few years, though, a season will have a fourth Full Moon. The third Full Moon to occur in one of these seasons is the once called the Blue Moon. Since the next Full Moon, which occurs some 15 hours before the winter solstice, is the fourth Full Moon of Autumn, the one just past is therefore the most recent Blue Moon. The next one occurs in the summer of 2013 with the Full Moon of August 21. Confused? Don’t be. Each phenomenon occurs with the same regularity.

The American celebration of Thanksgiving occurs this week, and even though the date for celebrating this national feast day wasn’t codified until the 1940’s, there is a marker in the skies that reminds us of what time of year it is. High overhead at around midnight is a bright, gold-tinted star called Capella, the 11th (and occasionally 10th) brightest star in the sky. Capella represents a she-goat, and in ancient Greek mythology she was the nurse of the infant Zeus, who, rambunctious boy that he was, accidentally broke off one of her horns. This horn was then endowed with the magical power to produce whatever the possessor wished, and so became known as the Cornucopia, or Horn of Plenty. The fact that this star is so prominent in our sky at this time of the year just happens to be a coincidence, but if you do notice it after your Thanksgiving meal, take the opportunity to count your blessings.

The evening twilight sky finds the return of the solar system’s most elusive naked-eye planet, the fleet-footed Mercury. You’ll find the reddish orb in the southwestern sky about half an hour after sunset by the week’s end. Look about 10 degrees above the horizon at around 5:30 pm. He’ll reach greatest elongation the following week.

Bright Jupiter is high in the south as evening twilight fades. The giant planet is very easy to find as soon as the sky begins to darken, and he’s in perfect position for observation once astronomical twilight ends. If you tire of Thanksgiving football, retire to the yard with a small telescope to be entertained by Old Jove as he beams down from across some 425 million miles of space. Modest sized amateur telescopes have been busy the last couple of weeks tracking a rapidly-changing feature in Jupiter’s atmosphere which may be the precursor of the return of the planet’s usually prominent South Equatorial Belt. Who knows what he’ll look like a week from now?

The morning sky features three bright objects to greet you before the Sun rises. Brilliant Venus is the easiest to pick out if you’re up an hour or so before sunrise. Just five degrees above the dazzling planet is the blue glimmer of the star Spica, and another 10 degrees above Spica you’ll see the golden glow of Saturn. Venus will pull away from the star and Saturn through the end of the year and into next. Spica and Saturn will be prominent evening sky sights by next spring.

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