StarWatch: Moravian College Astronomy

DECEMBER 2008

DECEMBER STAR MAP | STARWATCH INDEX | MOON PHASE CALENDAR

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Current Moon Phase

642 DECEMBER 7, 2008: Geminids Under Moonlight: On Friday, Geminid meteors are at a maximum; but while the number of shooting stars is escalating all week, so will be the moon’s brightness. The moon is full just hours before the Geminids peak at 8 p.m. EST this Friday. There is still every reason to suspect that despite the moonlight, brighter Geminids will still be seen if the heavens are clear, and you are facing away from the moon. Geminid meteors radiate from near Castor, the head of the mortal Geminid twin, whose immortal brother’s head star, Pollux, is just slightly brighter. If you’re facing the moon at 10 p.m., Castor and Pollux will be to the left and below. The strange story about the Geminids concerns its parent body which was a comet turned asteroid. In theory it is thought that many defunct comets have slipped into asteroid-like orbits, but only 3200 Phaethon has been linked with a meteor shower, the Geminids. Another curious aspect of Geminid meteors is that they were only first detected in 1862. Because of its very oval-shaped path (high eccentricity), which lies fairly close to Earth’s orbital plane (22 degree inclination), the gravitational perturbations of Jupiter are rapidly changing the direction of the shower’s major axis. In 1700, the Earth was outside the Geminid stream by 12 million miles. By 1900 this was reduced to less than two million miles. By the year 2100 the Earth’s orbital path will pass almost 10 million miles inside of the orbital path of the Geminids. Now is the sweet time for watching Geminids, and with rates of 80 meteors per hour on a moonless night, observers are bound to see at least a dozen or so shooting stars on a moon-drenched eve. Dress warmly, keeping head, hands, and feet toasty. The moon should always be to your rear. If the meteor traces itself back to the Twins, than you’ve seen a Geminid. A locator map is online.

643 DECEMBER 14, 2008: Io Saturnalia!: How low will the sun go? Like watching a dancer perform the limbo, ancient sky observers kept track of the sun’s rhythmic positions. They became especially watchful as autumn’s colder weather deepened and anxious over the prospects that the sun might just continue to lower until the big chill and eternal darkness consumed all life. On Saturday, December 21 we will get to witness noontime’s Sol at its “lowest” high position for the year. Of course, today all of this can be readily explained by the Earth’s 23.5 degree axial tilt from the perpendicular to its orbital plane. Not to be ignored is the situation that Earth’s axis maintains a consistent pointing direction. These two conditions give mid-latitude climes their four seasonal changes. The beauty from a scientific standpoint of Saturday’s low sun is the guarantee that Sol will be ever so slightly higher the following day. As a person who is decidedly in favor of spring and summer, I know that the snowy, cold days that loom ahead are painted against a portrait of a sun that will be steadily climbing higher and higher into the sky. Eventually, the sun’s increased altitude, which is tied into an augmented period of time the sun is above the horizon, will provide the necessary energy to dissolve the bitterness of winter into the more temperate days of spring. The Romans celebrated the low sun with the week-long festival of Saturnalia in honor of Saturn, the god of the harvest. It was at the winter solstice or sun standstill that Sol was reborn and would henceforth begin to rise higher in the sky each day, heralding the planting of crops in the spring and their eventual harvest in the fall. So this Saturday, may I propose a toast to the sun? Your lowly days will soon wane as sweet spring overtakes winter’s somber reign. Io Saturnalia! or "Ho, praise to Saturn...”

644 DECEMBER 21, 2008: With Every Breath That I Take: In a normal breath the average human being will inhale about 3 x 1021 atoms/molecules of air. That is a three with 21 zeros extending to the right of the number (3,000,000,000,000,000,000,000), three sextillion particles of air. The chemical makeup of that inhaled air will consist of about 78 percent nitrogen, 21 percent oxygen, and one percent argon. While in the lungs, oxygen molecules are diffused into the bloodstream through the alveoli, while carbon dioxide, quintillions (1018) of molecules, pass outward and take part in the exhalation. In the process of one respiration about 30 quintillion atoms of argon are inhaled and then exhaled. Throughout the geologic history of our planet, the nitrogen and oxygen in our air have been continuously recycled into organic and inorganic materials, but the argon has remained wonderfully fresh. Too heavy an atom to escape Earth’s gravitational pull and unable to combine with any other atoms, the argon content in our air has remained intact and has slowly grown from the beginning of time. In that one exhalation of 30 quintillion argon atoms, the wind patterns of the world will equally diffuse this argon so that after a year’s time, a day’s inhalation of air will contain about 15 argon atoms of that original breath. It is an astounding fact that with every lungful of air taken, we inhale the living evolutionary history of all times past, present, and future. The argon that you are breathing right now was in the lungs of a T-Rex 65 million years ago, and it was also in the lungs of every prophet, sage, saint, and sinner, who has ever lived. In fact, contained in a normal breath of air are 175,000 argon atoms that once reposed briefly in the lungs of Christ. That is in every breath of air that has or will ever be taken. Peace on Earth this Holiday Season.
Note: This article was adapted from an essay, "Breathing the Future and the Past," written by the American astronomer, Harlow Shapley (1885-1972).

645 DECEMBER 28, 2008: Year Ends with a Bang: On evening of December 1 the US experienced a superb close gathering of Jupiter, Venus, and the moon. The media carried the word that we would not see anything quite as stunning again until November 18, 2052. Indeed that will be a spectacular morning as Jupiter and the moon rise in near occultation followed by Venus. However, don’t fret. There are also good Jupiter, Venus, and moon events in 2017, 2019, 2022, 2032, 2034, 2036, and 2041. However, the only conjunction that happens in the early evening as did the December 1 event will occur on February 19, 2034. Not to fret because the moon, Venus, and Jupiter are not the only astronomical objects to tango with each other. On December 28 about one half hour after sundown, you’ll witness low in the SW a truly beautiful gathering of the thinnest, slivery moon followed by Mercury and bright Jupiter. Initially, you’ll probably need binoculars to spot fainter Mercury between the moon and Jupiter, but as the sky becomes darker, Mercury should become visible to the unaided eye. By that time however, the moon may have disappeared into the trees or below the horizon. Not to fear because the following evening, December 29, weather permitting, a more luminescent, fingernail moon will have jockeyed into the dominant position and will now stand above Jupiter, with Mercury closest to the horizon. This may be the best opportunity to catch all three relatively close to each other in a darker sky. But wait, there is more. On December 30 the moon begins closing on brilliant Venus, and Mercury nudges to within three lunar diameters of Jupiter. On New Year’s Eve the moon and Venus are nearly as close as they were on December 1, and Mercury and Jupiter are distanced by just over a degree ending the old year with a bang. Maps are online.