DECEMBER  2003

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380    DECEMBER 7, 2003:   Merrily Watching the Moon-Go-Round

Ask someone how long it takes the moon to orbit the Earth. If an answer is given, it is almost certain to be 28 days. Then ask how long it takes the moon to move through all of its shapes or phases. Again, an answer of 28 days will usually be given. The orbital or sidereal period of the moon is 27.3 days, while its phase or synodic period is 29.5 days. It is a fair assumption to hypothesize that the 28-day cycle to which people generally refer, results from the average of the moon's orbital and phase periods. The reason why these two periods exist at all is because the Earth orbits the sun, and its orientation in space which affects the lunar phases, is continuously changing. On Wednesday the moon will be close to Saturn in the east. Look between 9-11 p.m. When the moon returns to Saturn, it will have completed one Earth orbit, but not quite one phase period. Saturn, although not absolutely stationary, makes an adequate target because it is close to the moon and very bright. Using binoculars, you'll note that the moon's shape will not be quite round or full on Wednesday. Its upper limb will appear slightly flattened. The phase of the moon will be about two days past full. The moon returns to Saturn 27 days later on January 6, 2004 when it will have completed one sidereal period or one orbit around the Earth. On that evening the moon will be one day short of its full phase and its lower hemisphere, through binoculars, will not be quite round. The moon will return to its same phase on the ninth of January, 30 days from this Wednesday. At that time the moon's phase alignment with the Earth and sun will be the same. Since lunar phases and eclipses are a direct result of the 29.5-day synodic period, it is by far the more important cycle to remember.

381  DECMEBER 14, 2003:   A Winter Portrait

Twilight last Sunday evening was magical. A fresh, deep, snow-pack covered the landscape, and the sky at sundown was radiantly clear with a few scudding clouds and a nearly full moon rising in the east. Like last December, brilliant Venus was masquerading as the Star of Bethlehem. The only differences were that it now scintillated low in the evening southwest, instead of high in the southeast at dawn. Conditions were just right for that perfect winter portrait, but because of Venus's low altitude, I could not photograph it from my property. So off I went in my Tracker, digital camera and tripod in gloved hand, to my favorite haunt with a good western horizon. It proved highly unsuitable with Venus situated just above a tree line, complete with telephone poles and sagging wires. There was definitely no inspiration here. In winter the locations of sunset and the setting points for the planets that lie near to the sun, like Venus, are considerably south of west. For mid-latitudes in the Northern Hemisphere, this is the time of the long shadows and the shortest days. The sun is lowest in the sky and always in the south, rising south of east and setting south of west. During late spring and summer when the sun is north of the equator and high in the sky, it rises north of east and sets north of west. My favorite haunt had a great summertime view towards the northwest, but the scenery became uninspiring in the direction of where the sun sets in the winter. So off I quested along moonlit back roads and through well-kept neighborhoods sprinkled with white lights until I came upon a hilltop cemetery facing southwest. Here I found my perfect winter scene that also included Venus above a wooded landscape. You can see it at Web StarWatch at the URL below.

Venus as it appeared on Sunday, December 7, 2003 under a nearly full moon. Gary A. Becker digital photography...

Venus and Mercury can be seen in this late fall portrait. Mercury can is visible left of center just above the treeline in this digital photo taken on December 12, 2003 by Gary A. Becker.

382    DECEMBER 21, 2003:   Santa's North Star Navigational System

With tourists now being able to go to the North Pole as passengers on Russian icebreakers, information has become available concerning how Santa Claus finds his way from the North Pole to the towns and cities that he needs to visit on Christmas Eve. Some of these passengers have even had private meetings with the "Man in Red" to discuss his techniques when his busy schedule permits. Here is what they've found. Generally speaking, Santa uses a low-tech approach for finding positions that could be called the North Star Navigational System or NSNS for short. It uses the North Star, sometimes called Polaris, as the chief navigational marker for finding latitude. Latitude is an angular measurement made from the equator, northward or southward, to the location that contains the place of interest. As an example, my wife and I live in Coopersburg, PA at latitude 40.511 degrees north. The altitude or height above the horizon of the North Celestial Pole, the point in the sky about which the heavens pivot due to the Earth's rotation, is the same 40.511 degrees. The North Star lies very close to this position, making it an excellent reference for helping to find localities north of the equator. In flight, Santa uses Rudolph's red nose as an artificial horizon marker to measure the angle above the horizon of the North Star, and then directly converts this into a latitude position. Thank goodness, there is only one Coopersburg in the United States. Even in situations where the same town or city name is found in several different spots, there has been little problem when utilizing the NSNS method for place location. Hopefully, more facts will emerge, especially with regard to how Santa calculates the other necessary coordinate, longitude. Happy Holidays!

A Holiday Program has been an ASD Planetarium tradition since its founding in 1965. Composite digital photography by Gary A. Becker...

383    DECEMBER 28, 2003:   Saturn at Opposition

When you are opposed to someone's ideas or attitudes you have a perspective that is opposite to that view. In astronomy we have a similar condition for the planets and other celestial bodies as we watch them continuously changing their positions in the sky with respect to the sun. On New Year's Eve, the ringed world, Saturn, will be in opposition to the sun. Unlike the negative connotations that opposition has in language, to be at opposition in astronomy is a very good quality. It means that the location of the object is opposite to the sun in the sky. Remember when Mars was at opposition late last August? It was big, it was bright, and it was visible all night! This Wednesday, it will be Saturn's turn to be at opposition and rise in the ENE as the sun is setting in the WSW. But there will be some differences. Because of Saturn's 900 million mile distance from the Earth, it will not be nearly as bright as Mars was last summer. Saturn will, however, be the dominant object in the east until Sirius, the Dog Star, rises just after 7 p.m. The size of Saturn and its ring system through a telescope will be what impresses observers the most. From ring edge to ring edge, Saturn will look almost four times larger than Mars at its best. So if you were disappointed by Mars' small appearance in your telescope last summer, Saturn should prove simply inspiring. To add to its magnificence, we are currently observing Saturn tipped back looking at its underbelly, viewing the southern hemisphere of the planet and seeing the rings from below with nearly the greatest amount of ring area visible. The best time to view Saturn is between 9 p.m. and 3 a.m. when it is higher in the sky and is less affected by atmospheric motion. See Web StarWatch at the URL below for a map.