Nightskies_dec_1

Jeff Green | Dec 01, 2005

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Gray MerriamLegaleseGeneral information and opinion on legal topics by Rural Legal ServicesNature Reflectionsby Jean GriffinNight Skiesby Leo Enright

The Night Skies of December:Brilliant Venus leads a December parade of planets

by Leo Enright

Locally, during the whole month of December, the time of sunset varies by only about 8 minutes. On December 1, sunset is at about 4:25 p.m., and it occurs only a few seconds (not minutes!) earlier each evening until December 10, when it is at 4:24 p.m., locally the earliest sunset of the whole year. Then sunset is only a few seconds later each evening until by the end of the month it is at 4:33 p.m. Meanwhile, sunrises are occurring a little later each day – from 7:25 a.m. on December 1 to 7:47 a.m. on December 31. The latest sunrise of the year does not occur until January 3. (Most people do not realize that, at this latitude, the date of earliest sunset is over 3 weeks EARLIER than the date of the latest sunrise.) People who have a good view of the horizons (southwestern and southeastern), can easily see that the most southerly positions for both the sun’s setting and rising are on December 21, the date that is called the Solstice, which literally means “the sun standing still.” Since late June, the sun’s setting and rising positions on the horizon have been moving southward, and now they stop that movement and begin to go northward again. Just as the sun, from this latitude, appears to be weaker and further south in the month of December than at any other time of the year, the December Full Moon is at the opposite extreme. The Full Moon on the nights of December 14 and 15 (the exact moment of Full being a bit before local noon on the 15th) is the northernmost Full Moon of the whole year. Weather permitting, on those two evenings, it may be seen rising, not in the East, but in the northeast, and it appears almost straight overhead by midnight. When it sets the following mornings, it will be seen not in the West, but in the northwest.

This is the month to enjoy winter’s bright star patterns in the southern sky when there are more bright stars than at any other season. Foremost among them is the easily recognized constellation Orion the Hunter marching across the sky, followed by his faithful dogs, Canis Major and Canis Minor. In a straight line leftward from the three bright stars in Orion’s Belt, we can easily see Sirius, the brightest star in the whole sky, marking the eye of the big dog. The smaller dog nearby has Procyon, the sixth brightest star, to mark its location. Orion himself has very bright stars to mark his head, shoulders, and knees, as well as the famous trio that marks his belt. Below his belt, in what is sometimes called the Sword of Orion, is what astronomers call the Orion Nebula, a vast area of hydrogen gas with many new stars emerging – young stars that are only a few million years old! Though easily seen with the naked eye on a clear moonless night, this nebula is a truly wondrous sight in large binoculars or a small telescope. Orion is well up in the southeast by 8p.m., and his canine companions are easily seen in the same direction by 10 p.m. Also, noteworthy in December are the bright stars forming the constellation Cygnus, the Swan, or the Northern Cross, standing above the northwestern horizon in the evening.

The parade of planets is quite remarkable this month. In fact, all five of the very bright planets are easily visible. The parade starts right at sunset, or maybe even before, if people remember where and when to look, because Venus is now bright enough to be seen in daylight. Though it is as bright this month as it ever gets, it is still fairly low in the southwest and may be seen from sunset until it sets about two hours later, and less than two hours later in the last week of December. Observers with a small telescope will notice that the planet’s disk appears larger from night to night, and at the same time the illuminated part becomes thinner, like a Quarter Moon changing into a slender crescent. Reddish Mars, which has appeared fabulously bright over the past two months (as it came unusually close to the planet Earth, and as Earth was “passing on the inside of its orbit” making it appear to move in retrograde motion), is the planet that we should observe the most carefully of all. Several things occur this month. First of all, as Earth pulls away from Mars and the distance between them increases, it will begin to appear slightly fainter. Careful observers will notice that, though it is still very bright, as December progresses, it will no longer be brighter than Jupiter, or even than the star Sirius. Very careful observers may also notice that the apparent westward, or retrograde, motion will end on December 10, and Mars will begin to move in its normal, or eastward, path across the sky. As it does, it will appear to get closer to the famous star cluster called the Pleiades. Saturn, which rises in the east at about 9 p.m. in early December and much earlier by late December, is unusually bright and has just begun its retrograde motion. Careful observers on moonless nights will be able to see the planet in its slow “left-to-right” (or retrograde) movement very near the group of stars called “the Beehive Cluster”. On nights with a moon in the sky, use binoculars to observe Saturn among the stars of this famous cluster. With a small telescope, the disk and the amazing rings of Saturn will appear larger than usual. The remaining two planets are in the morning sky. Jupiter, still bright enough to dominate its part of the heavens, may be easily seen in the southeastern sky from one to two hours before sunrise. Mercury, a planet which many people have rarely, if ever, seen, will be easily found for the entire month by those who have a fairly good view of the southeastern horizon and look down and to the left from Jupiter, over a period from 30 to 60 minutes before sunrise, and (Remember this!), if the weather cooperates, Mercury may be found at those times ANY day of the month. With this in mind, it would be a good month to try to see all five planets, especially for those who have never seen Mercury!

The moon and planets give us several beautiful conjunctions this month. After sunset on December 4, the moon and Venus have a beautiful pairing in the southwestern sky. In the early evening on December 11, the gibbous moon and Mars are a beautiful pair in the eastern sky. On the night of December 18, the moon appears close to Saturn. On December 27, in the southeastern sky at about an hour before sunrise, the waning crescent moon is slightly below Jupiter; on the 28th at the same time, it is about half-way between Jupiter and Mercury; on December 29, the very slender crescent moon is slightly to the right of Mercury. Be sure to take out your binoculars to see that one; the lunar crescent will be very thin.

Two meteor showers reach their peaks in December – the Geminids from December 12 to 14 and the Ursids on December 22. Even though bright moonlight will interfere somewhat, clear nights for the Geminids almost guarantee some bright and memorable “shooting stars”. It is often best to look southeastward for the Geminids and northward for the Ursids. Try spending an hour in order to catch some of the “fireworks.”

More information about observing the winter sky is available in the book The Beginner’s Observing Guide, which is now available at Sharbot Lake Pharmacy. It might be a good Christmas gift suggestion. I wish all readers a blessed Christmas and a safe and very happy holiday.