December is an exciting time not only for Christmas but for three exciting events to observe: the Geminids meteor shower, the great conjunction of Jupiter and Saturn, and the Ursids meteor shower. Vernon from the Callander and West Perthshire U3A Astronomy group tells us more about these three notable events and what to look out for this month.
It is always helpful to have a star chart to follow when navigating and observing the heavens. A free star chart which also contains lots of additional observational notes is published monthly by Skymaps. Simply go to skymaps.com and scroll down to ‘Download the latest issue’. From here you will can download the northern hemisphere version and save it. This is then best printed double sided to an A4 sheet. It is worth noting that planets do not appear on skymaps. In this note of astronomical events I have only included items that can be seen either with the naked eye or with a pair of binoculars.
Should you venture outside you will need a torch. Use a red light head torch if you have one, or put red plastic over a torch to illuminate the skymap and preserve your night vision which improves greatly over time. Wrap up warm and with a little perseverance, about 20 minutes, you will feast your eyes on the universe that you live within. Enjoy and indulge!
The Great Conjunction
“The Great Conjunction” of Jupiter and Saturn with best views on 20th, 21st and 22nd which is best seen through binoculars 40 minutes after sunset low on the southwestern horizon where the two planets merge into one bright object. “Behold a star in the East” is what the shepherds are reported in the Bible to have said when they saw a very similar conjunction, in what is now calculated to be year 7AD.
With Ursa Major further east it is easier to see the fainter stars in the southern most part of the constellation. The Great Bears smaller brother Ursa Minor can be seen swinging from Polaris (the north star). Above Polaris is the feint Camelopardalis with Lynx to its right further east. To the west, above Polaris lies Cephus followed by Lacerta which just above Cygnus in full flight. Higher and further still to the west we see The Great Square of Pegasus from which it is easy to see the constellations limbs stretching out from Aquarius in the west to Andromeda high in the north above Cassiopeia.
At around 10pm due south, on the line of the ecliptic, the arc line the Moon and planets follow across the sky, is the beautiful Pleiades open cluster. The Pleiades have appeared in folklore and legend around the world for millennia. A native American tale portrays them as lost sisters chased by a bear; Aztecs of Mexico set their calendar around them; Celts used these stars to mark a holiday between the autumn and winter that eventually became Halloween. Today we refer to them as the Seven Sisters (although there are hundreds of stars in the cluster) that were annoyed by Orion because he kept bothering them. They turned to Zeus for help and he turned them into doves and later stars where he set them in the sky. Six of the stars are almost always visible, the seventh when conditions are good. These are best viewed in binoculars.to reveal their true beauty.
The Hyades cluster lies just below Pleiades and represents the face of the constellation Taurus, the Bull. Pleiades indicates the location the Bulls shoulders. Hyades, the most prominent star cluster in the entire sky, contains several hundred stars and is around 150 Light years from Earth. It was formed around 600 million years ago. Taurus is a mega constellation that is actually shaped like a Bull. The alpha star, Alderbaran, marks the Bulls eye then the horns stick out into space in the east while its body trails behind. Ancient people saw these stars as a bull as long ago as 5000 years making Taurus one of the oldest identified shapes in the sky. Within Taurus lies Crab Nebula (M1). The supernova, that caused the nebula,1054AD, was highly visible to the naked eye and historical records from China, Japan, Korea and Arabia suggest it was visible for around one month.
After six months away from the night sky we can see Orion standing tall to the east of Taurus with the three stars of Orion’s Belt making it instantly recognisable. Within Orion there is the fuzzy star in the middle of sword, in binoculars it is an extremely bright cloudy patch. If you are fortunate to have access to a telescope you should start to see three or four stars inside a luminous patch. This is the Orion Nebula that is so beautifully photographed by the Hubble Telescope. Try Google search and type “M42” into your browser.
To the west Aquarius has disappeared and Cetus is lower, but Pisces and Aries are readily seen with Triangulum and Andromeda above. The Great Square of Pegasus is dipping towards the western horizon and because its orientation is different it appears more like a diamond, standing on one point, than a its usual square shape.
The last major meteor shower of the year, the Geminid shower, is active between 3rd and 16th with a peak period on the 13th and 14th which fits in with a New Moon making conditions ideal. This is one to share with the children not only because it is one of the most active of all meteor showers, sometimes peaking at 100/hour, but because it has a high activity rate before midnight.
The Ursid meteor shower is active between 17th and 26th peaking on 21st and 22nd. Normally the Ursids produce around 10 meteors per hour.
Mercury continues to decline in altitude above the Eastern horizon disappearing from the dawn sky by the 19th. It reappears to the west during sunset at the end of the month.
Venus is less than a degree south of the waning crescent Moon on 12th. The illuminated part of the planet increases from 89% to 94% but because it is travelling away from the Earth its apparent diameter is decreasing so that the magnitude, or brightness of the planet remains the same at -4.0 throughout the month.
Earth experiences a total solar eclipse on 14th when a New Moon briefly obscures the Sun. The path of the eclipse is from the South Pacific to the Southern Atlantic making a narrow landfall on Chile and Argentina.
Apart from the Moon, Mars remains the brightest object in the night sky. It is well placed for observation in the faint constellation of Pisces shining at magnitude -1.1 at the beginning of the month and finishing at -0.2.
Jupiter and Saturn will be just 0.1 degree apart on 21st making this their closest conjunction since 1623 when they were separated by 0.09 degree. The occurrence during 1623 could not be observed because the two planets were just 12 degrees from the sun. 2020 is much better for us because the planets are 30 degrees East of the Sun making them visible in the evening sky. The best time to observe is between 30 minutes and 1 hour after sunset when the sky is dark enough and the planets at least 10 degrees above the horizon. If your view to the east is obscured by the hills or mountains, try either observing a little earlier or looking from a more favourable location ensuring you have good easterly views.
Johannes Kepler (1571-1630) was a German mathematician and astronomer who studied planetary orbits. He was the first person to propose the triple conjunction of Jupiter and Saturn in the year 6 or 7 BC as an explanation for the Star of Bethlehem. This idea was repopularised by Prof. David Hughes of Sheffield University who suggested that the Magi were astrologers who read astrological significance into the event. Other astronomical explanations include a supernova, a bright comet, or even a triple conjunction between Jupiter and Regulus followed by a conjunction of Jupiter with Venus. Each explanation has its strengths and weaknesses and since historical records are silent on the matter, astronomers will continue to speculate on the correct answer in the years ahead.
Uranus ends the year visible in the evening sky in Aries, magnitude 5.8, not setting until after midnight.
Neptune is in Aquarius, magnitude 7.8, setting around midnight.
Nights of interest
Some of the objects described below are expressed in degrees from the Moon. This is far less complicated to measure than you might think. To measure 10 degrees, hold your hand up towards the sky at arm’s length and turn your hand up so that it obscures part of your view. The width of your hand is 10 degrees and holding just one finger is two degrees.
8th Dec – Moon, Last Quarter.
11th Dec – Comet 141P magnitude +8.8 passing through Aquarius 15 arcminutes west of +3.8 Epsilon Aquarii. This Comet is the same brightness as planet Neptune and can be seen using binoculars or a small telescope.
12th Dec – 07.00 hrs provides great views of Venus above the southeast horizon.
12th Dec – Total solar eclipse of the Earth, Southern hemisphere.
12th Dec – Moon at perigee, nearest to Earth, 361,000 km.
14th Dec – New Moon.
13/14th Dec – Geminid meteor shower, maximum at 00.50hrs.
18th Dec – Orion centre stage at midnight with red supergiant Betelgeuse and blue supergiant Rigel showing at their best.
21st Dec – Winter Solstice marks the longest night and the shortest day of the year for the northern hemisphere.
21st Dec – Moon, First Quarter.
21st Dec – The Great Conjunction. Jupiter and Saturn are at their closest since 16th July 1623.
22nd Dec – Ursid meteor shower maximum at 03.00 onwards.
23rd Dec – Conjunction of Mars and the Moon.
30th Dec – Full Moon.