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The Sky This Week
U.S. Naval Observatory's Weekly Blog
Shadowing the Groundhog
by Geoff Chester, USNO Public Affairs
26 January 2021
Mars and Uranus, imaged from Alexandria, Virginia on 2021 January 22, 01:38 UT
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor and a Canon EOS Rebel SL2 DSLR.
The Moon begins the week among the stars of Gemini, high on the ecliptic plane. Full Moon occurs on the 28th at 2:16 pm Eastern Standard Time. January’s Full Moon is known in folklore as the Wolf Moon or the Moon After Yule. Names for each month’s Full Moon come to us from many traditions and typically reflect the climate conditions that characterize the particular month. In January, typically winter’s harshest time, people in northern climes noticed that wolves tended to gather in packs to hunt for food in the frozen landscape.
February 2nd marks one of those annual observances that has become a kind of unofficial holiday that we now call Groundhog Day. The origins of this occasion can be traced back to medieval Europe, when landowners collected rent from their peasant tenants. These payments were fixed by the dates of the astronomical seasons as well as the dates that fell midway between the seasonal markers. The equinoxes and solstices were known as “quarter days” while the mid-points were called “cross-quarter days”. In Celtic lands these cross-quarter days were widely observed, with the one marking mid-winter known as “Imbolc” loosely translated as “lamb’s milk” since it heralded the beginning of lambing season. With the arrival of Christianity the Celtic festival became incorporated into Candlemas, February 2nd, the 40th day after Christmas when the infant Jesus was presented by Mary and Joseph at the temple. The celebration of Candlemas spread throughout Europe, especially among Germanic peoples. They introduced the idea of using animal behavior to predict the arrival of spring, noting the activity (or lack thereof) of native badgers. The tradition arrived in America with the so-called Pennsylvania Dutch, who adopted the groundhog as the animal prognosticator. The first chronicled observance of the day in the U.S. dates back to 1840, and since 1887 it has been an annual rite in the town of Punxsutawney, Pennsylvania. Thanks to the popular movie released in 1993 it has become something of a worldwide “viral” event. Some other cross-quarter days that we still observe are May Day and Halloween, which have similar origin stories. The actual mid-point in this winter season occurs on February 3rd.
The combination of a Full Moon at a high northerly declination produces bright skies that block most of the splendor from the winter night’s sky. However, the bright stars of the Great Winter Circle continue to shine through the glow. Over the first couple of nights this week Luna may be found in the vicinity of three of the circle’s bright members. North of the Moon on the 26th you’ll find Castor and Pollux, the “Twin Stars” of Gemini. The mythology surrounding the twins is very complicated and varies among many ancient writers. Some considered them mortal, while others gave them divine immortality. Homer, it seems, saw them as both. They both die in The Iliad, but in The Odyssey he describes them as “having honor equal to gods”. Of the two stars, Pollux is the brighter and closer at a distance of 34 light-years. It is an evolved “giant” star, the closest of its kind to the solar system. Castor, on the other hand, is really a six-star system. If you point a small telescope at it you can see the two brighter components. Each of these has been revealed to be double through spectroscopy while a fainter, distant pair orbits the four bright ones. They all lie about 51 light-years away.
South of the Twin Stars is Procyon, the brighter of the two stars that define Canis Minor, the Little Dog. Like its brighter neighbor Sirius it is one of the closer stars to the Sun at 11.5 light-years, and has a “white dwarf” companion star. The existence of this fainter object was first postulated by the German astronomer Friedrich Bessel, and for many years it was the subject of intense study by the world’s largest telescopes, including USNO’s 26-inch “Great Equatorial”. It was finally found in 1894 with the larger 36-inch telescope at Lick Observatory.
Mercury can still be spotted about 10 degrees above the southwest horizon half an hour after sunset. The innermost planet is easiest to see early in the week. He fades rapidly as he begins retrograde motion back toward the Sun. By the end of the week he will be very hard to find.
Ruddy Mars remains the sole bright planet to grace the sky. His warm glimmer can be found high in the west as evening twilight fades. He is moving steadily eastward under the three stars that outline Aires, the Ram, and in a month he will pass just south of the Pleiades star cluster. Last week he passed to the north of the far-flung planet Uranus, delighting many owners of small telescopes.
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