february2009nightskiesovertanzania

February 2009 Night Skies over Tanzania

NIGHT SKIES OVER TANZANIA

FEBRUARY 2009

By Dr N T Jiwaji

ntjiwaji at yahoo dot com

CLICK ON MAP FOR LARGER IMAGE

This month we are preoccupied with catching a just visible comet Lulin in the night sky as it makes its closest approach to Earth on February 24^th. It then begins its swings around the sun which will fling it back to the depths of outer reaches of our solar system where it originated from in the Oort cloud that surrounds our solar system at a distance of around one light year; close to the nearest stars. The Oort cloud consists of material left over from that which formed our sun and planets. This material, once in a while, due to gravitational pull of the nearby stars, gets pushed into an orbit which allows the sun to pull it towards us. We call it a comet when it is close to us. It is like a dirty snowball consisting of ice and dust and when it is close to the sun the ice vaporizes and the dust is pushed away from the comet by the solar wind hence creating the tail of the comet.

The comet that is close to us now is called ‘Lulin’ and was discovered by a student in China. In order to see it you will need to be up after midnight or wake up early before dawn. It rises in the East after midnight in the constellation of Virgo and is high in the sky at dawn. It is just barely visible if you get a night with dark skies without the moon, but it should be quite easily seen with a pair of binoculars, which is the best way to see it since you can scan the eastern skies to locate it. New Moon is on 25^th February so a few days around that day should be ideal for viewing the comet.

Another story making the news is the discovery of an earth like planet orbiting a star. Since such planets are very far away from us, they can only be detected by their influence on the motion of the star around which they orbit. Hence only about 300 have been found so far. Recently one planet was spotted directly by extremely large telescopes and this opens the door for new discoveries. Earth like planets around other stars are raise the possibly of being suitable to sustain life.

The night sky this month continues to be dominated by brilliant Venus, but Saturn is waiting in the wings to show itself by the end of the month. Venus continues to approach us and remains very bright. Although it is changing into a crescent phase its brightness does not change appreciably since its apparent size also increases, which compensates for the reduction in the sunlit area facing us. Through the telescope it shows up as a beautiful crescent which is an even thinner this month and is often mistakenly thought to be the moon since we are so used to seeing a crescent moon. With a good pair of binoculars, you might be able to make out Venus’ crescent shape. At the beginning of the month Venus sets just before 9 pm but by the end of the month it will set soon after 8 pm.

At the end of the month on 27^th and 28^th February, the Moon and Venus will once again be close together for the fourth time in consecutive months. This can also be expected to be an eye catching show in the western horizon soon after sunset. On 27th Venus will be above the Moon while on 28th it will be below the Moon.

Saturn rises late in the night, but by 18^th February it rises in the east at 8 pm. It can be difficult to distinguish among the stars since it is not so bright, but if you watch it closely it will not twinkle while a nearby star will twinkle appreciably. This way of differentiating planets from stars works best when they are well above the horizon since the thicker atmospheric path near the horizon makes all light twinkle.

If you are an early riser, the pre-dawn skies offer the view of Jupiter, Mars and Mercury close to the horizon in the East just before sunrise with Saturn setting at the other end in the west. You will note that all the planets are found in a narrow path in the east west direction. This is because all planets orbit the sun in an almost flat plane hence in the skies they appear only in the east-west line.

This month’s penumbral lunar eclipse on 9^th February proved that during this type of eclipse we just cannot notice any difference in reduction in the brightness of the moon, although from our location the moon was fully immersed in this very thin shadow.

The Milky Way crosses the sky from north to south with the bright band of myriads of stars and nebulae visible almost overhead at 8 p.m. throughout the month. ORION, GEMINI, TAURUS, and PERSEUS constellations mark the band clearly. A new addition this month is the FALSE CROSS, an asterism that has mislead many a seafarer because it closely resembles the SOUTHERN CROSS whose long diagonal points south but the False Cross’s diagonal does not. Locate it after 9 p.m. as it rises in the southeast. LEO (the lion) pops its head above the eastern horizon at 8 p.m. just as Saturn rises above the eastern horizon. The whole Leo constellation should be easily recognizable by 9:30 p.m. Five of the top ten brightest stars can be recognized using the star map: the brightest star is Sirius, followed by Canopus the second brightest star that can be seen towards the south. Rigel is in ORION , Procyon is to the east, Achernar will be setting in the west and Betelgeuse is in ORION. After 10 p.m. they will be joined by Alpha- and Beta-Centauri the brightest stars rising below the SOUTHERN CROSS.

You can get a chance to control the Hubble Space telescope by participating in making a decision which object it should observe and photograph. You can participate by visiting the website http://YouDecide.Hubblesite.org and picking from a choice of six options by 1^st March. The Hubble photograph of the most chosen object will be released during the International Year of Astronomy project, 100 Hours of Astronomy, from 2-5 April when people all over the world will be looking at the night skies and doing various astronomy activities.

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