JANUARY STAR MAP
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JANUARY 1, 2012: Fastest, Closest in January
H a p p y N e w Y e a r ! The Holiday rush may be behind us, but for the Earth, the first week in January means that itís moving at its fastest pace. In fact on January 5 at 7 p.m. EST, the Earth reaches this location called perihelion which is also its closest position to the sun. That may seem strange, especially since we are approaching the coldest time of the year, but for the Earth the seasons have nothing to do with distance and everything to do with the change in the sunís angle or its altitude in the sky. This changes because the Earthís axis is tilted. The variation in Earthís distance from the sun causes its orbital velocity to change. When the Earth reaches perihelion, the gravitational attraction between it and the sun are at a maximum, and the Earth responds by moving fastest. This has a curious effect on the seasons because it makes the period of time from fall through winter about a week shorter than from spring through summer. A week may not seem like much time, but a little more summer is always preferable over winter. Because its orbital speed is always changing, Earth cannot revolve around the sun in a circular path. Its orbital shape is oval in contour, an ellipse to be precise. Two points of interest called the foci, connect to the boundary of the ellipse in such a way that the distance from focus one to a boundary point, plus the distance from the same boundary position to focus two, are always the same for any point along the ellipse. At one focus the sun is found; at the other focus, only an empty point in space exists. Opposite Earthís perihelion position and along the longest axis of the ellipse, called the major axis, lies Earthís farthest position from the sun, identified as aphelion. Earthlings wonít have to consider being there until July 4, 2012 at 11 p.m. EDT., around the time that most fireworks extravaganzas will be ending along the East Coast.
JANUARY 8, 2012: 2012: A Big Year Ahead
The lineup of astronomical events for 2012 is about as good as it gets. Early in the year, January through March, Comet Garradd, C/2009 P1, may attain naked eye visibility from rural locales. Currently visible in the morning sky during January, by mid-February, Garradd will be observable all night, but best seen after midnight. One month later the comet will be well-placed throughout the night in the north between the cup of the Big Dipper and the North Star. Currently peak brightness is predicted for March, but binoculars will still be needed to spot Garradd from the suburbs. Mars is bright during March in the constellation of Leo the Lion, and on March 13, look for Venus and Jupiter to be only three degrees apart after sundown. The moon plays among these planets on February 25-26 and March 25-26. Venus passes through the Pleiades star cluster on April 3, and Saturn is bright in the spring sky during April and May. A sunset ringed solar eclipse passes from Crescent City, CA through mid-Texas on the evening of May 20. Dead center along its path is the Grand Canyon and Albuquerque, NM. Bryce Canyon, UT and Chaco Canyon, NM are also good locations. Not to be outdone is the transit of Venus across the sunís disk on June 5. Miss this one and you will have to hang around until 2117 or 2125. Yes, that is over 100 years. Meteor showers are also exceptional for 2012. The Lyrids (April 22), the Perseids (August 13), the Orionids (October 21), the Leonids (November 17), and the biggest display of them all, the Geminids (December 13) all fall on dates with minimal interference from the moon. It just does not get any better than 2012. All of these events are visible from the United States over your house if the skies are clear and you live in a suburban location, with the exception of the solar eclipse. If you have ever wanted to get involved in astronomy, 2012 is the year.
JANUARY 15, 2012: A Horizon for All Seasons
As I write these words near mid-January, my new North Face winter jacket hangs idly in the closet patiently waiting for winter to begin. Maybe weíll skip this dreaded season altogether and emerge into an early spring. I thought about this the other evening as I exited my SUV in a light jacket. It was about 6:00 p.m. Looking towards the NW, I spied a madly scintillating star across the street near the tree line. It was Vega, the brightest luminary in the constellation of Lyra the Harp. Vega is also the brightest star of the Great Summer Triangle, an asterism of two seasons ago, and yes, still visible low in the west and NW. I like seeing constellations at odd seasons of the year, such as winterís Orion the Hunter rising in the predawn hour of mid-August while watching for Perseid meteors. Now the winter group featuring Orion, Auriga the Charioteer, Taurus the Bull, Gemini the Twins, and Canis Major and Canis Minor, the big and little dogs are on the rise in the east at the same time the Great Summer Triangle is on the wane in the west. Due south at 6 p.m. and nearly two-thirds of the way up in the sky will be found bright Jupiter. To Jupiterís right and slightly higher in the sky can be found the four vivid stars that form autumnís Great Square of Pegasus the Flying Horse. Find the two stars farthest to the right in the Great Square and follow them downward towards the horizon. On the way, it will be impossible to miss radiant Venus to the right, the brightest object of the night except for the moon. Keep trekking downward and just before reaching the horizon will be lonely Fomalhaut of Piscis Austrinus the Southern Fish. Looking NE near the horizon, the bowl of the Big Dipper is beginning to point upward, a sure indication that winter, at least astronomically, must give way to spring. There are the leftovers and appetizers of all of the seasons along the lowly horizons.
JANUARY 22, 2012: Season of the Young Moons
I was amazed to see the sun setting slightly more than a half hour later than its earliest setting time which occurred last December on the 8th. Even though we are in the midst of the meteorological winter, the coldest time of the year, we are rounding the corner and soon signs of a higher, warmer sun will become evident. Speaking about higher suns, another object, the moon, is also fun to watch because of its steep ascent into the spring evening skies after its new phase. The moon orbits the Earth nearly in the Earthís orbital plane called the ecliptic. The angular difference is just over five degrees. In late winter and early spring, the ecliptic is tilted steeply to the western horizon, so that the first four or five days after new moon, Luna will seem to rise almost vertically from the western horizon after sundown. The effect is best witnessed after the new moon nearest to the vernal equinox, the first day of spring, but now is a great time to start ďyoungĒ moon watching. The moon is new early on Monday, but will still be too close to the sun that evening to be visible. By Tuesday, however, look for a razor thin crescent about 10 degrees above the WSW horizon, 45 minutes after sundown. The moon will be just three percent sunlit. By Wednesday, an eight percent lit crescent approaches brilliant Venus above and to the moonís left. Thursday, Luna is 14 percent sunlit, and now it is located above and to the left of Venus. During the following three evenings a thickening crescent approaches Jupiter, so that by Monday, January 30, a quarter moon, half on, half off is near Jupiter for the first five hours of the evening. Keep in mind that if bad weather prevails during the week, there will be replays occurring on the evenings of February 22-25, March 23-26 (probably the best sequence), April 22-25, and May 21-24. It is more evidence that spring is just around the corner.
JANUARY 29, 2012: The Analemma Dilemma
Have you ever seen that elongated figure eight on a globe? Usually placed in the Pacific Ocean far away from any land masses, it is called the analemma. If you would observe the sun each day of the year, at noon, and start with the sun due south (June 12), you would see several effects. First, because the Earthís axis is tilted, you would notice the height of the sun changing above the horizon. The sun would appear highest at summer solstice and lowest six months later at winter solstice, but another more subtle motion would also be viewed. As the sun was changing its altitude, it would appear to move to the right and left of the due south position. In other words, as the days passed, your watch would say 12 noon, but the sun might be to the left or to the right of due south. The combination of the change in the height of the sun and its motion to the right or left of south would create the analemma in the sky. Our clocks beat to an average rhythm called mean solar time which has been standardized into time zones and then further modified to daylight saving time during the warmer months. Each day at noon, one p.m. for daylight saving time, an imaginary or fictitious sun is due south by this convention. As the Earth revolves around the sun, it shifts the sun about one degree to the east each day. We correct for this by adding an extra four minutes to the Earthís spin period to create the mean solar day. But the eastward shift of the sun is not uniform. This results from Earthís speed varying due to its elliptical orbit. Another change in the sunís eastward motion results because the sun moves northward and southward with respect to the celestial equator. This is created by Earthís axial tilt. This combination of motions may put the real sun ahead of our clocks by 16 minutes and behind by just over 14 minutes. A detailed analemma is online at the URL below.
Behold, the analemma
as modified slightly by the author from Wikipedia