DECEMBER  2011

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798    DECEMBER 4, 2011:   Dark Days of Winter

Let me get this off my chest. I HATE WINTER! It’s not so much the wind and the cold or the fact that I keep my study cooler to save a little on energy. It’s all of that darkness, the long winter nights that drive me bonkers. As a positivist who tries to view the glass half full, there is a faint glimmer of hope in the air. The earliest sunset will be occurring this week is on the 8th to be precise. For my earthly location, sundown will be happening at 4:34 p.m. After that date, the sun goes down later, not much later at first, but then picking up speed so that by mid-January people start noticing the effect. This does not mean that December 8 is the shortest day of the year. That happens two weeks later on the 22nd when the time between sunrise and sunset is at its shortest. This is known as the winter solstice. The latest sunrise happens on January 5 when coincidentally the Earth is closest to the sun. The reason why earliest sunsets and latest sunrises do not take place on the shortest day of the year is because timekeepers follow the motion of a fictitious or mean sun which moves uniformly over Earth’s equator. The eastward motion of the real or apparent sun varies from day to day because Earth revolves in an oval shaped orbit. This makes the sun change its position fastest in the winter and slowest during the summertime. In addition, the Earth’s axial tilt causes the sun to move northward after the winter solstice and southward beyond the summer solstice. This slows the eastward motion of the sun against the stars which is created by the orbiting Earth. The result is that the real sun gets ahead of or behind the mean sun which is the time kept by the government and our house clocks. Currently, the real sun reaches noontime seven minutes ahead of the mean sun, causing sunsets to occur earlier than expected, with the earliest sunset occurring on Thursday.

799    DECEMBER 11, 2011:   Star Bright?

Unless you are in a large city, viewing the sky on any clear night reveals dozens to thousands of stars. A few will be bright while many will be faint. Astronomers quantify stellar magnitude with a system where more negative numbers indicate brighter stars. When we casually view the heavens, it is impossible to know whether stars are dazzling because they are close to us or brilliant because they are more distant and very luminous objects. Conversely, a faint star may be really bright but very distant, or close and simply dim. To discover the true luminosity of the stars, it is necessary to know their distances. This is accomplished by measuring their angular displacements (parallaxes) across a standard baseline and solving a simple trigonometric problem. To demonstrate the concept of parallax, hold a finger six inches in front of your nose and wink your eyes back and forth. The finger will appear to jump with respect to more distance objects. Hold the finger farther away and the displacement becomes less when the eyes are winked. We have been successfully measuring the parallaxes of stars since 1838, but since the Hipparcos mission of 1989-93, astronomers have precise parallaxes for over 100,000 luminaries and less accurate data for an additional 2.5 million stars. Knowing the distances to stars allows astronomers to move them mathematically to a standard position of 32.6 light years for comparison. That may seem like a weird number, but it signifies a parallactic shift of 1/10 second of arc. A degree can be divided into 3600 seconds. Moving the most vivid nighttime star, Sirius, to 32.6 light years would make it just brighter than the stars of the Big Dipper. Orion’s stars, however, would become powerhouses, shining with the brilliance of Jupiter, Venus, and beyond, easily casting shadows on the ground in rural locales at night with some being visible even in the daytime.

800    DECEMBER 18, 2011:   Low Sun, High Hopes

This has been a strange autumn, at least for those living along the Eastern Seaboard. After coasting along under mild conditions during most of October, we were lashed by a crippling nor’easter on the 29th, the earliest major snowfall in recorded history. Within a week the ice was gone and so was the cold snap. Through November, most outdoor activities happening during the afternoon hours could still be conducted with just a light jacket. Now that we are approaching the Holidays, more seasonal conditions have become apparent, but the air still does not have the bitter bite of December. The National Weather Service’s long range forecast through mid-January predicted a much colder than normal autumn with higher amounts of precipitation and multiple major winter events before the New Year. Autumn seems to have pounced early, and then rolled over to play dead. Even if the meteorological chronometers are having trouble ticking to the calendrical dates, the clockwork universe “tocks” to a precision that cannot be denied. The sun’s southward motion has slowed to an almost imperceptible rate and will halt completely on the morning of December 22 at 12:30 a.m. EST, to be precise. Old Sol will be at its winter standstill position, or as astronomers call it, the winter solstice. Fall will be gone, and winter will be upon us. At that moment I plan to be outside listening very intently to the first telltale sounds of “creaking” as the sun reverses itself and begins that barely noticeable rise against the celestial vault. It will take a month before people start to perceive the slight increase in the length of daylight, and another month before cars parked in the afternoon sun begin to feel cozy upon entering; but gradually the changes will occur as the sun continues to climb ever higher into the sky, melting winter into a budding spring. I guess you could simply call it high expectations for a low sun.

801    DECEMBER 25, 2011:   Cold Quadrantids Await

The one page article in Sky and Telescope magazine began with “Have you ever seen a single Quadrantid meteor? I smiled because I had seen a whole bunch of them back in the mid-1970s. My single Quadrantid observing experience involved taking a group of students to Pulpit Rock, my local astronomy club’s dark sky observing site west of Allentown, PA. The evening started cold and windy, but clear. Then it got partly cloudy; and then it snowed for a while. Afterwards it got even colder. One of my students forgot his gloves. He was the lucky one because he got banished to the car. Those were the days when observing meant staying out the entire night; that’s 15 hours in early January. You may have already guessed that my stalwart group and I did not last for more than a couple hours—four to be exact. But we did see Quadrantid meteors flash in between scudding low clouds and more during a few clear patches. Except for the big chill that comes along with winter star watching, this year is idea for Quadrantid viewing. The shower peaks between 2-3 a.m., EST, January 4th, and the moon sets by 3 a.m. The Quadrantid shower has a very short duration of maximum activity, so by 5 a.m. things should be pretty much over. Be outside by 1:30 a.m. Face NE and observe near the zenith, usually the darkest part of the sky. If shooting stars seem to be fanning away from a location below and to the left of the Big Dipper’s handle, you will be seeing Quadrantid meteors. Make sure head, hands, and feet are well insulated against the cold. Long johns are a must and so is a sleeping bag. Consider purchasing disposable charcoal hand and feet warmers from a local hardware store for added comfort from the cold. Remember, even if you see nothing, the best part of Quadrantid watching is the long, hot shower that awaits your reentry into the house at the end of the night.

Quadrantid meteors will radiate from below and left of the handle of the Big Dipper during the morning hours of January 4. The best time for watching is between 2-3 a.m. This map is set for 2 a.m. on the date of maximum. Dress warmly, get comfortable in a sleeping bag, and face towards the NE when viewing. Meteor rates will vary, but dark site locations can expect to see between 40-200 meteors per hour. Suburban rates will be less than half this amount. Map created by Gary A. Becker using Software Bisque's The Sky...