Sky Notes for December 2012, with James Abbott #stargazing
The Winter Solstice occurs this year at just after 11am on Friday 21st December. Being near midday, this lowest Sun of the year gives an opportunity to see the longest noon shadows – if the clouds co-operate and stay away. The noon Sun will be just under 15 degrees above the horizon from mid-Essex. From the north of Scotland the Sun does not even reach 10 degrees in altitude.
The low Sun and short days reduce opportunities for Solar observations. Currently activity is moderate. Daily updates for sunspots, flares, aurora and more can be found at http://www.spaceweather.com/
NASA is holding to the prediction that the current Cycle 24 will be relatively weak, perhaps the weakest for a century. Although there have been a steady stream of active Sunspot groups rotating across the Sun, activity is still well short of the levels seen at recent maxima, particularly the years around 1980 and 1990: http://solarscience.msfc.nasa.gov/predict.shtml
The short days are matched by the longest nights of the year but it is actually only fully dark for 12 hours due to winter twilight. It is often said that in mid-winter it is dark all the time in the Arctic. This is not true in the more populated areas of the Arctic where twilight can give several hours of reasonable light, although the skies need to be clear to get the most benefit.
Jupiter is at opposition on December 3rd when it is not only at its brightest for the year, it is also close to its highest possible declination. Jupiter will be visible all night and reaches around 60 degrees in altitude at midnight, located in Taurus. The high altitude offers the best chances of good seeing as the planet is being observed through a reduced path length through the atmosphere than when at a lower declination.
There will be a fine conjunction between the nearly full Moon and Jupiter on Christmas Day evening. At around midnight the Moon will be passing less than 1 degree below Jupiter and by watching the relative positions of the 2 objects it will be possible to see from hour to hour the motion of the Moon to the left in the sky which is its real motion in orbit around the Earth. The Moon is Full on the 28th.
The Geminids are the most active meteor shower of the year and the circumstances are very favourable this month, with the Moon close to New on maximum night which is expected to be December 13th/14th. As their name suggests, the meteors appear to radiate out from the constellation of Gemini, near the bright star Castor, the higher of the Twins.
The best time to look will be from about 8pm on the evening of the 13th when Gemini will be in the East, and then through to after midnight when it is in the South.
Meteor showers are caused by streams of dust orbiting the Sun which the Earth passes through at certain times of the year. But these streams are evolving all the time. The Geminids were not recorded prior to the 19th century but have now become the most active of annual showers and appear to be getting even stronger. Under the best conditions, an observer might see 2 meteors per minute on maximum night. The brightest are often yellow in colour. Most showers have been linked to comets but the Geminids are unusual as their parent body is the asteroid 3200 Phaethon.
James Abbott is an astronomer, NEAS member and CfDS Regional Information Officer.
Posted on 4 December, 2012, in Astronomy News, Popular Science, Stargazing and tagged asteroid, aurora, geminids, jupiter, meteor shower, meteors, Solar. Bookmark the permalink. Comments Off on Sky Notes for December 2012, with James Abbott #stargazing.