December Night Skies over Tanzania
The change is nearing. Change from 2015 to 2016. Be ready to be make unintended mistake when writing the year next year after so many months of writing 2015. Children born close to the end of 2015 will counted one year older while those born at the beginning of 2016 will be taken to be one year older – so unfair! when only a month or two separate them. However this type of confusion at changeover is quite tame and mild compared to the mess that can happen when your flight is a few minutes past midnight and the ticket shows the flight is the following day but when you have to arrange for a taxi you take you to the airport the previous day to be in time for the check-in a couple of hours before flight time!!
Luckily, such confusions are experienced by only a very few people since most people are peacefully asleep while the day is changing its date at midnight. I always thought that it is strange that the day changes date at midnight when there is nothing practical changing! The end of evening at sunset would be a more natural change of date since the previous day’s hard work has ended at 4 or 5 pm and you are ready to start the next day after sunset at around 6 pm with a relaxing time with your family and a good night’s sleep. This is indeed the natural change of date observed by many traditional cultures.
However, with the modern life that we live nowadays, the day cannot end at 6 pm since there are so many important things to do for the next four or five hours – homework for students, finalizing the report for the boss, or going for a dinner date or cinema for the lovebirds. We cannot imagine giving up these, can we? However, imagine the confusion that would arise for so many people if the date was to change at sunset. In such a system, if you ask someone to meet you at 9 pm it would already be the next day which can make the person not show up at the agreed time!! Let us be thankful that dates change at midnight while the vast majority of people are sleeping.
Even for astronomical time keeping, there had to be a redefinition of Universal Time (UT) which began at midday at 0 degrees longitude. In order to avoid confusion and misunderstanding betwee dates before and after the changeover, the Universal Coordinated Time (UTC) begins its day at midnight.
December has an important date for world geography due to an astronomical factor of inclination of the Earth’s axis by 23.5 degrees to the solar plane. On December 22, called the southern solstice, the Sun is at its southernmost position. At this time the Sun is directly overhead at latitude 23.5 degrees south, and that latitude is named the Tropic of Capricorn. Days are longest and nights are shortest in the south while the south polar region experiences 24 hours of daytime. At this time, in the north days are shortest while nights are longest and the north polar region experiences 24 hours of night.
Planet-wise, December night skies are completely dry of visible planets since they have all shifted to the early morning dawn skies. The sky map this month is for dawn and you can see Venus extremely bright near the eastern horizon while very bright Jupiter is almost overhead. Red Mars is beginning its approach towards Earth in its orbit and is still far so it is a reddish point star in between Venus and Jupiter. Saturn is another point star close to the east horizon.
An interesting thing to observe now it that the four planets, Saturn, Venus, Mars and Jupiter all lie on an almost straight line. This is because all their orbits around the Sun line on a flat plane when we watch them in the sky from Earth, our eyes are actually aligned along the solar plane.
The planets are shifting fast in the sky so their positions change a lot during this time. Venus is moving away from Mars at the moment in the dawn sky, while Venus and Saturn are closing in, and by 9 January they will be closest. On New Year’s eve you will see a beautiful half Moon rising like a golden bowl in the east followed closely by brilliant Jupiter. A very attractive sight also awaits us in the dawn skies near the east horizon on January 7 when the crescent Moon joins the Venus-Saturn pair to show a beautiful triplet.
New Moon is on December 11 while the first quarter is on 18 December when the Moon is seen as a half disc and will be overhead at sunset. This is the best time to see the craters on the Moon through a telescope. Christmas day will be marked by a Full Moon on December 25.
The night skies are beginning to display many prominent constellations in the sky. The glory of the southern hemisphere’s night sky becomes apparent when you go out after 9 pm. The brightest star in the sky, Sirius, is now quite prominent in the south-east as the neck star in the dog shaped constellation Canis Major (Big Dog).
An arch of the dense band of stars in the Milky Way starts the evening straddling the eastern horizon. It then rises cutting approximately north to south and band reaches the zenith by midnight. The band begins with Canis Major, the dog, crossing to magnificent Orion, the hunter, which then leads to Taurus the bull, which contains the distinctly visible red giant star, Aldebaran. The last two constellations in the Milky Way band are Perseus containing the famous variable star Algol, and at the very end is the M shaped Cassiopeia in the north.
In the early evening skies you will see the red giant star Aldebaran, the brightest star in Taurus. It rises in the sky as the night passes and is imposingly overhead by 10 pm. Close to Taurus is the famous twinkling star cluster, Plaiedes, also known as the Seven Little Sisters’. Just off the arch westwards but still close to the Milky Way can be found the Square of Pegasus.
The Andromeda galaxy is 2 million light years away from us, yet we can still see it with naked eye and appears as a small patch of nebulosity in dark skies. It lies about 40 degrees above the north horizon between the Square of Pegasus and Perseus.
The most easily identifiable constellation is ORION which we see as a huge rectangle laying on its side in the eastern sky. It has two very bright stars at the end of its diagonals: Rigel on the top right and the red giant star Betelgeuse sparkling red on the bottom left of the rectangle. The other diagonal is marked by three stars close together in the middle, called the ‘Belt of Orion’. It is embedded in a dense cloudy nebulosity of interstellar matter which is and active nursery of new stars as the unstoppable pull of gravity gathers the interstellar gas and dust with the passage of millions of years. The Orion nebula can easily be made out with the naked eye and is breathtaking in a small pair of binoculars, or even better, a telescope.
Among the Zodiacal constellations that span east to west, are Gemini the twins cutting into Taurus, leading to less prominent Aires, Pisces, Aquarius, and Capricorn and ends with Saggitarius setting in the west swamped by sunlight. There are also several stars that you should try to identify because they are among the brightest in the sky. In the last half of the month Procyon rises in the south east with Sirus, already high and Canopus in the south: These three brilliant stars form an almost straight line and together with Capella also rising in the north east, forms a reasonable right angle triangle.
The end of the year provides three brilliant passes of the International Space Station (ISS) on 26, 27 and 29 December with the most spectacular overhead pass across the center of the sky on 27 December while on 26 and 29 December it will be close to the south-west horizon. The overhead pass on 27 December will begin with ISS rising from northwest horizon at 7:30 pm and ends 10 minutes later at 7:40 pm disappearing below the southeast horizon.
The ISS pass on 26 December, which begins at 8:26 pm rising in the northwest horizon, will end abruptly in mid sky at 8:33 pm above the southwest horizon, when the space station enters the Earth’s shadow. It is quite a sight to observe such a sudden change in the skies so look out for this spectacle.