Imbolog – 2015

   Watch That WoodChuck!
groundhog newspaper   On February 2, we watch for the groundhog to emerge for reasons that originate from ancient Celtic tradition. Groundhog Day was known as lmbolog, or sheep’s milk, a time for nurturing young sheep and planting spring crops. The belief arose that if lmbolog were to be sunny and clear, then winter’s effects would endure, foreshadowing a long winter. How­ever, if skies were overcast, then the warmer days of spring would arrive early. To farmers then and today, an early spring means early spring plant­ing and a subsequent early harvest. Often fires were lit to commemorate the event as fires were a sign of warmth and light, both of which increased as days lengthened.
not a meteorologist   German immigrant farmers are credited with bringing Groundhog Day with them to the United States as they settled in Pennsylvania. To them, February 2 was called Candlemas Day, because of the practice of lighting candles on this day in celebration of early planting. The Germans believed that the badger was able to predict the weather on the basis of whether or not its shadow appeared. If the badger, or groundhog, saw its shadow on Candlemas, it would be scared and return to its burrow for another six weeks to sleep through the long winter. However, if the skies were cloudy then no shadows would appear, and an early and warm spring would be expected. The importance of this day to German immigrants, and its impact on their farming gave rise to the couplet:
         A farmer would rather see his wife upon a bier,
         than that Candlemas Day should be sunny and clear.

puxs-phil-lied   Year after year, since 1898, crowds have gathered in Punxsutawney, Pennsylvania, on February 2 to wait for a certain groundhog to emerge from its burrow. Today the belief in this as a predictor of weather is not nearly as consequential as it appears despite all the hoopla created by the news media. Yet, there is some scientific rationale to this ritual, albeit not in the accuracy of the forecast. When the skies are clear, temperatures tend to be cold as the ground radiates heat absorbed during the day back into the atmosphere; and when skies are over­cast temperatures tend to moderate as clouds trap heat nearer the ground.
Groundhog-Standing2   To other cultures in the Northern Hemisphere Candlemas Day was celebrated as the midpoint, or cross­ quarter day, between the winter solstice and the spring equinox. Cross-quarter days occur midway between the astronomical events that mark the beginning of each of the four seasons, the solstices and the equinoxes. The second cross-quarter day of the year, as it is calculated mathematically, occurs on May 6, although it is often associated with May Day, on May 1. The third cross­ quarter day of the year is August 7, the only one of the four without a significant event associated with it. Mid-autumn, the fourth cross-quarter day, occurs on the last day of October, Hallowmas Eve, or as we now know it, Halloween.
   Interestingly this system of equinox, solstice, and cross-quarter days has led to some confusion as to when the seasonal midpoints and endpoints occur. For example, June 21 is the official date for the start of summer in the Northern Hemisphere, but it is sometimes referred to as midsummer’s day. This would suggest that summer actually begins on May Day and ends in early August. In a similar manner, December 21, the start of winter for the Northern Hemisphere, is some­times referred to as midwinter’s day. This would imply winter actually begins at the end of October, and concludes (assuming no shadow is seen) on Groundhog Day.
groundhog   So will we have a long winter, or will it be short, and our spring be an early spring? No one can predict this, at least not based on seeing one’s shadow. However, come this February 2, rest assured that crowds will once again gather to watch Punxsutawney Phil emerge from his hole.
   Adapted from “Watch that Woodchuck” Scope on the Skies. Science Scope Magazine. February 1993.

Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

December Solstice 2013

sagittarius-dec21   On Saturday, 21 December, at 11:11 CST (17:11 UT) the Sun will have reached its southernmost distance (in degrees of latitude and/or declination) from the Earth’s surface and celestial equator. Using Geographical coordinates the Sun is over the Tropic of Capricorn at a latitude of 23.5o South. Using Astronomical coordinates the Sun is -23.5o South (declination) and 18Hours RA (right ascension).

December Solstice
seasons   In its annual trek around the Sun the Earth reaches certain orbital positions that define the beginning and end for each of our four seasons. In either hemisphere, northern or southern, we learn these as the spring equinox, summer solstice, autumn equinox, and winter solstice. However the seasons are reversed or the opposite for each hemisphere. Winter in the northern hemisphere, for example, starts when summer in the southern hemisphere begins, and so on. This gives rise to the idea that it may be more practical to simply refer to these dates by the month that it occurs in. So for example rather than saying this is the “winter solstice” and then specifying which hemisphere you are referring to folks in either hemisphere would know which solstice, equinox, and or season it is by simply stating the name of the month for that event, i.e., December Solstice, March Equinox, June Solstice, September Equinox.

Along the Ecliptic
   How are the dates for these changes of seasons selected? As the Earth revolves around the Sun the Sun appears to move eastward against the stars in the background, regardless of the hemisphere. The apparent path the Sun follows is known as the ecliptic and in reality it is the orbit of the Earth superimposed on the stars in the background. seasons on ecliptic-aniAs a rule the starry sky is referred to as the celestial sphere, an imaginary sphere surrounding the Earth on which the ecliptic, stars, planets, and our Moon are located. The Earth’s equator and lines of latitude and longitude are likewise superimposed on the celestial sphere. This is a system similar to the use of latitude and longitude on the Earth’s surface that allows for the positioning or plotting of celestial objects including stars, galaxies, and closer to home the location of the Sun and orbiting planets.

   With regard to the Sun there are specific locations along the ecliptic that mark the change of seasons that correspond to geographic locations on the Earth’s surface. In the northern hemisphere we traditionally say that the Winter Solstice (change to December Solstice) (first day of winter) occurs when the Sun is south of the equator over the Tropic of Capricorn. The Spring Equinox (change to March Equinox) (first day of spring) is when the Sun is over the Earth’s equator. The first day of summer or the Summer Solstice (change to June Solstice) is when the Sun is north of the equator and is over the Tropic of Cancer. And finally when the Sun is back over the Earth’s equator it is the Autumn Equinox (change to September Equinox) and the start of autumn.

Mid-day Sun at 40oNorth

Mid-day Sun at 40oNorth

   These dates are more precisely determined by when the Sun has reached a specific astronomical coordinate on the celestial sphere. However without knowing the calendar date or astronomical position one can easily determine this date by observing the Sun’s apparent daily path regularly.
   In the northern hemisphere on the first day of winter during December the Sun will be south of the equator and will follow the shortest apparent path from east to west. It will rise in the southeast at its furthest south point from due east and set in the southwest at its furthest south point from due west. Midway between rising and setting the Sun will be at its lowest mid-day point above the southern horizon. In contrast it is the start of summer in the southern hemisphere during December. From those latitudes the Sun will follow its longest apparent path from east to west. The Sun will rise in the southeast at its furthest south point from due east and set in the southwest at its furthest south point from due west. Midway between rising and setting the Sun in the southern hemisphere would be at its highest mid-day point above the northern horizon.

The View From South of the Equator
   Keep in mind that these observations are based on the direction one typically faces to view the apparent path of the Sun follows between rising and setting. This direction is always toward or relative to the Earth’s equator and is centered mid-way between due east and due west. It is also latitude-dependent in that the length of daylight and night varies with latitude – more hours of daylight close to the equator where the Sun’s apparent path takes it higher above the horizon and subsequently giving more time above the horizon. Moving away from the equator the Sun’s apparent path doesn’t take it as high above the horizon and thus less daylight time. Nonetheless those in the northern hemisphere face toward south while those in the southern hemisphere face toward north. Remember – the Sun and all other celestial objects always rise in the east!

Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.