December night skies over Tanzania
Dr. N. T. Jiwaji
ntjiwaji at yahoo dot com
Click here for larger sky map for Dec 2008
The December 1 spectacle (see here) was an eye catcher that was noticed by thousands of people all over the country. However it mystified a lot of people who saw it as a sign from the heavens. Good or bad? Since we in Tanzania were very lucky to see the wide eyed crescent smile in the heavens, it was definitely a good – it was a sign to learn about the mysteries of the heavens through the science of astronomy. In fact just that one even can teach us a lot of science of the heavens. Since the spectacle appeared only on that one day, and changed completely the next, there must be some movement of the objects out there - which identifies the stars as actually planets (which is derived from Greek, meaning ‘wanderers’). We know the two planets as Venus and Jupiter. Venus continues to move rapidly leaving Jupiter behind, and is scheduled to reach its maximum elevation of 47 degrees at sunset on 14th January 2009. We can understand the movement if you picture the planets in our solar system revolving around the sun. [diagram]
Even the way the moon appeared teaches us a lot. Why does the moon appear as a cresecent? If you imagine it as a ball and the sun as a torch shining on the ball from below, you can easily try this out and you will see a beautiful crescent where the torch strikes the ball. Not only that, we saw the disc of the whole moon clearly marked out and was visible as a faint outline. If the sun hits the moon on one side, the other must be in darkness, so there would not be any light that would make it visible to us? So why is it visible? It is because the light of the sun reflected by the earth reaches the moon’s dark side and which again gets reflected back to us, hence making it faintly visible.
A very attractive spectacle again awaits us in the western skies at sunset on 31st December, which marks the beginning of New Year’s eve. We will see the moon very close to Venus by about 4 degrees which is about eight moon diameters apart. It should be an eye catching experience also. Through a telescope Venus is seen as a half shape and slowly changing to a crescent. This is another question that is worth knowing why. The reason is similar to why we see the moon as a crescent – so use your imagination to view the position of Venus which allows light to strike it from the side as viewed from earth.
Closer to the horizon in the light of the setting sun the same day, Mercury and Jupiter will close up just a moon width apart. It would be a good opportunity to see the elusive Mercury after locating Jupiter which will be brighter of the pair. Two days earlier on 29th December, Mercury, Jupiter and Moon will form a trio with the moon above the two planets about 4 moon-widths away. Mercury should be visible from 14th December once it goes above 10 degrees above the horizon at sunset. During this cycle, Mercury will reach its highest elevation of 19 degrees above the horizon at sunset
The bright and starry constellations are on their way again after having relatively scant skies over the past few months. The constellations that can be seen rising in the east but a bit late at the moment and which are most recognizable are: (from south-east) SIRIUS, ORION and TAURUS in the east, PERSEUS and CASSIOPEIA in the north, and finally CYGNUS in the north-west. Try to locate the Andromaeda Galaxy about 40 degrees above the north horizon in an area of the sky between the Square of PEGASUS and the PERSEUS constellations. At 2 million light years, it is the most distant object that can be seen with the naked eye! Through a telescope, you can see its elliptical shape and perhaps the spiral structure, similar to what our own Milky Way Galaxy is. Other brilliant start clusters are the Pleiades and the Hyades in Orion and Taurus respectively.
The Geminid meteor shower peaks on 13th December so you may see (the lucky) shooting stars if you are out around and after midnight. However the almost full moon will reduce the number of shooting stars that you will see. 21st December is a day of solstice (stationary sun) that marks when its apparent movement in the sky southward comes to a halt and will turn back north towards. On that day the sun will be overhead at latitude 23 ½ degrees south also known as Tropic of Capricon. It is often called “winter solstice”, a term coined by northern civilizations; but remember it also marks summer time for southern peoples.
The International Space Station (ISS) is set to make a pass in the evening skies as a brilliant light gliding slowly across the sky. Today (Saturday 13th December), it will be seen around 7:30 pm rising in the north west and passes close to Jupiter in the west. It will set in the south east seven minutes later. On Monday 15th December, it will again make a showing at around 6:45 pm and will pass below Jupiter close to the western horizon and will go below the horizon six minutes later. Understand that the ISS is a huge football field sized space station so we see it brilliantly because of the sunlight reflected from its outer surface. One more thing to learn from watching the skies. Interest yourself in many other wonders in the sky, even those that you cannot see by visiting the website www.astronomy2009.ac.tz, and absorb the excitement of the International Year of Astronomy which is set to start in only 17 days, from the beginning of January.
astronomy2009.ac.tz