December 2009 Night Skies over Tanzania

Though this year was a bit of disappointment for those who enjoy eclipses, they will not remain disheartened for long. There is a New Year gift waiting for them. The first is in the final hours of this year while a far more precious reward for the long wait will be presented two weeks later.

On 31^st December with the moon in Full phase, a small portion of the Moon, about eight percent, will be hidden from view during the partial eclipse of the Moon. Just before 10 pm, at 9:53 pm when the Moon will be in the east, about half way up the sky, the moon will slowly begin to be covered from the bottom by the Earth’s shadow. In the next half hour, by around 10 30 pm, about 8% of the moon will be covered up. After that, in the next half hour, the Earth’s shadow will slowly move away and will leave the Moon from the top at 10:53 pm. This is indeed a New Year gift, delivered at the right time!!

A very nice animation of how the Moon moves throgh the Earth's shadow can be seen at this website: http://www.shadowandsubstance.com/

Another spectacle awaits us two weeks later on 15^th January from7 in the morning until 11 am. A major part of the Sun will be blocked from view during the eclipse of the sun. Actually it is an “annular eclipse” for some lucky observers in Uganda and Kenya and across the Indian Ocean to India and China. They will see the Sun almost fully covered up except for a thin ring (called an annulus) around the central dark disk of the Moon. However in Tanzania we will see not see the ring, but will see from 80 to 90 percent of the Sun being covered up. This will cause a very huge change in the morning daylight.

An amination of the Solar Eclipse can be seen at this website: http://www.shadowandsubstance.com/

During a Lunar Eclipse, the Earth comes directly between the Sun and the Moon, while in a Solar Eclipse the Moon is in an exact line between the Sun and the Earth. From Earth, we see that during a Solar Eclipse, the tiny Moon covers up the mighty Sun. Why is this so? The Moon is very small compared to the Sun (400 times smaller) while it is also the same 400 times closer to us than the Sun. Hence in the sky, we see them having the same apparent size. This is not easy to see directly since you would be blinded by the Sun if you tried to look at it directly (SO NEVER DO IT!), but if you had special glasses it is quite eye opening to compare the size of the sun during the day with the size of the full Moon during the night.

To demonstrate this effect, if you extend your hand and hold out your small finger and point it towards the Full moon the whole Moon will be covered up. Is your finger the same size as the Moon? Of course not, but both the Moon, and your small finger extended at arm’s length, are half degree apparent size. This is a very useful way of measuring angles in the sky. Holding out the first finger at arm’s length covers about 1 degree of the sky, while a thumb will cover about 2 degrees. A clenched fist held out at arm’s length covers about 10 degrees in the sky.

Jupiter shines bright as ever in the evening sky now in the western horizon as it slowly shifts from east to west as the days go by. It is a guest worth entertaining since it will be with us for only a couple of months more. By the beginning February it will be difficult to see in the glare of the setting sun. A beautiful pairing of a crescent Moon and Jupiter will be seen on 21st December with the two separated by 6 degrees (about 4 fingers apart).

Neptune is very close to Jupiter at the moment. So with larger telescopes you can see a starlike point just away from Jupiter but far from its four Galilean moons that are easily recognized since they are always arranged in a straight line along the planet’s equatorial plane. It is closest to Jupiter on 21^st December.

Mars rises late, after 10 pm, and can be recognized as a brilliant red star close to the eastern horizon.

Mars is now in the stage of retrograde motion since 20th December. Retrograde means opposite, so this describes the opposite way that Mars is moving currently. Normally ALL planets (and the Moon) move from West to East. Our normal observation of for example the Moon is that it moves from West to East, since we know that during New Moon the Moon is in the West while as the days go by it appears further and further East until after about 15 day it will appear in the East rising at sunset. Hence movement from of planets and the Moon from East to West is rather contrary to our intuitive understanding. The term “retrograde” tries to capture this dilemma.

The only way to notice this retrograde movement of planets is by comparing their positions against the fixed background of the stars and constellations.

The way we can notice this retrograde motion of Mars is by comparing its position against the background of stars in the background. Before December, Mars was constellation of Pices, Fish and had shifted day by day towards the constellation of Leo, the Lion in its normal motion. At the moment, since 20^th December, it has started shifting away slowly from Leo back towards Pices, that is in the opposite, or retrograde direction. This will continue until the beginning of March 2010 when it will be closest to Pices constellation and its movement will turn back towards Leo and resumes its normal motion in the sky.

A very nice animation of retrograde motion of Mars can be seen at this website: http://www.shadowandsubstance.com/

Read here more about how and why we get retrograde motion.

The Moon is new on 16^th December, first quarter on 24^thth January. on Christmas eve and full Moon will be on New Year’s eve, the day of the partial Lunar eclipse. Last quarter will be on 7th January.

This month's full Moon is a “Blue Moon” because there was another full Moon during this month on 2^nd December. The term “once in a blue moon” has come about because it is very rare to have two full moons in one month.

The bright and starry constellations are on their way in again after having relatively scant skies over the past few months. The constellations can be seen rising in the east but a bit late at the moment. These 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, CASSIOPEIA 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 star clusters are the Pleiades and the Hyades in TAURUS contellation.

Locate and identify the bright stars names in the sky map. These are among the brightest stars in the sky. The brightest and the second brightest are Sirius and Canopus respectively. The other bright stars are: blue Rigel and red giant Betelguese both in Orion, and the red giant Aldebaran inTaurus. Others are Capella, Deneb and Altair all in the northern half of the sky while Achernar is in the South together with Canopus.

The Geminid meteor shower peaks on 13^th December and it one of the meteor showers that regularly shows ten or twenty meteors per hour. Watch after midnight in the area of the Gemini constellation which rises in the east at that time (so it is not seen in the map also). This time there will be no Moon to brighten the sky, so you are like to see many shooting stars after midnight all originating from the east.

21^st 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) will make a glorious pass over our evening skies on two occasions this month: on 27^th and on 29^th December. On 27^th it will rise from the south west horizon just after 7:50 pm and will rise to almost overhead skies up to 45 degrees, pass close to Jupiter and near an almost full Moon. Thereafter, it will suddenly disappear from view in mid sky just before 7:50 pm near in the north west direction

On 29^th the ISS will make another brilliant pass crossing the whole sky from horizon to horizon, rising in the south west just after 7 pm and will rise to an elevation of almost 62 degrees. It will pass very very clsoe to Jupiter, a sight not worth missing. It will finally set in the north east after about 5 minutes, around 7:10 pm.

The excitement of the International Year of Astronomy has taken us through this year, exposing us to activities and issues that have set the minds on fire, pondering the mysteries of our cosmos extending from earth to the farthest reaches of our Universe so that we can try to understand it scientifically. The year is coming to a close, but the wondering, the thinking and the actions will continue on.