Thursday, December 31 2009 @ 02:40 pm EST
Contributed by: dgrosvold
Blue Moon Endings
Fantasy image of a Blue Moon
The Full Moon on Thursday, December 31st marks a rare ending this year. There are normally 12 full lunar cycles in a year, but some years have 13. The thirteenth moon is sometimes known as the Blue Moon. Although different definitions place the blue moon at different times of the year, at least one definition places it at the end of the year.
A March 1946 article in Sky and Telescope
magazine by James Hugh Pruett misinterpreted the 1937 Farmer’s Almanac to mean that the second full moon in a calendar month was called the Blue Moon. This “misinterpreted” definition of a Blue Moon has come into widespread use in recent years after it was revived on the January 31, 1980 installment of the popular radio program StarDate
There are several other astronomical definitions for a “Blue Moon”, but the two cited above make this coming Thursday’s Full Moon a Blue Moon
. By either definition, this only happens every few years. Just remember — it’s referred to as a blue moon
, but the Moon won’t look
blue — it will look the same as any other full moon.
In any event, it’s an appropriate way to punctuate not only the end of 2009, but the end of the only decade in a thousand years where we’ll refer to the year as “something-thousand-something” rather than the more common “nineteen- or twenty-something-something.” I guess a situation like that only happens “once in a very blue moon...”
The Wandering Stars
Sky view looking east at 9:30 PM on Jan 2, 2010
, in Greek, means wanderer
. These objects are so named because they appear to move from night to night against the fixed background of the stars. A feast of planets is visible in the evening sky this week, even with the glare of the Full Moon.
, known as the King of Planets
, will be visible as a bright object low in the southwest just after sunset. Jupiter sets in the west by about 9:00 PM, and will only be visible in the evening sky for another month or so. After that, it sinks below the horizon before sunset - too early to be seen for observers in our part of the world. Binoculars or small telescopes will reveal Ganymede, Callisto, Io, and Europa, the four brightest moons of Jupiter. Observing these at different hours of the night and on subsequent nights will show obvious movement with respect to each other and Jupiter. So far, scientists have discovered over sixty three moons orbiting the giant planet.
is approximately 1-1/2° lower toward the western horizon than Jupiter, and is much harder to spot. A small telescope will reveal it as an obvious disk with a blue-green cast, rather than as a point source. You can measure 1° on the sky by the width of your pinkie finger held at arm’s length. Neptune will set only about 6 minutes earlier than Jupiter.
presents a great observing target for those who might be awake in the early morning hours. Saturn’s rings are at just 4° from edge-on right now, so the planet looks much like a “spike in a ball” in small telescopes. The ring angle will open somewhat in 2010. Saturn will be rising in the east just before midnight, and will be appear to be a bright object with a slightly yellow cast. Small telescopes will reveal the rings and perhaps up to six of Saturn’s brightest moons — Titan, Hyperion, Rhea, Dione, Tethys, and Mimas. These will be stretched out along the same plane as the ring system. Of all the moons in the Solar System, Titan is unique in that it is the only one that has an atmosphere. Saturn has over sixty-one known moons.
rises big and bright at about 8:00 PM and should be visible all night. Mars is in one of it’s close approaches (or opposition) to Earth during the month of January, and should be easy to observe. Small telescopes should show enough detail to see the markings or “canali” that lead early observers to believe there was an active civilization on the Red Planet. These markings were first observed by Giovanni Schiaparelli
during the opposition of 1877, and he dubbed them canali, which is Italian for canals or channels. Improved astronomical observations in the early 20th century proved this to be false. Look for Mars in the east as a brilliant object with a ruddy hue. On Saturday, Jan 2nd, Mars and the Moon will rise together about 7° apart in the eastern sky. For reference, 7° of sky is about the width of four fingers held at arm’s length.