March 2009 Night Skies over Tanzania
NIGHT SKIES OVER TANZANIA
MARCH 2009
By Dr N T Jiwaji
ntjiwaji at yahoo dot com
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The International Year of Astronomy is well underway and many activities are being undertaken. The “Globe at Night” project which can done by anyone who is interested in preserving the view of the stars for posterity. The culprit here is light pollution which is depriving us the enjoyment of marveling at the myriads of stars. In Dar es Salaam, we can see only about 200 to 300 of the brightest stars, while two to three thousand remaining stars are hidden from our view behind the glare of the light reflected by the atmosphere from too many lights on the ground that are leaking their brightness upwards. In more developed parts of the world, such as Europe and the US, the light pollution of their atmosphere is compounded by bad weather so world people cannot see ANY stars. There is a global campaign for dark skies awareness by discouraging wasteful light from being directed upwards to the sky. This will in turn save energy (and cost) and reduce environmental pollution.
In Tanzania the problem is not as severe if you are well away from the urban centers. Hence in most parts of Tanzania we still see all the stars in their full glory. The sky map shows the brightest stars Sirius and Canopus as pointed stars. Other bright stars are shown as spots whose size depends on their brightness. The smallest black dots have a brightness of magnitude four. Fainter stars that can only be seen in rural environment where there are no major sources of light pollution are shown in the map as background dots. These are of magnitude 5 and 6. Stars of magnitude greater than 6 cannot be seen with the naked eyes and is the limit of human visibility. Due to light pollution in cities, municipalities and large towns, the faintest stars that can be seen with the naked eyes are of magnitude 3 or lower (note that the lower the magnitude, the brighter the star is). When there is a Moon in the sky, even the magnitude 3 stars may not be seen easily. More exotic objects such as galaxies, nebulae, ‘dust’ bands, comets etc. are also blocked from our view. At best we can see not more than 300 of more than 2000 stars that should be visible at a time in the night sky. This shows how much of the natural beauty we are missing just because a huge amount of light is allowed to escape uselessly upward into the dusty air. We need to make just a small effort in awareness and dedication to arrest this growing problem before all the beauty of our urban skies is wiped out.
To assess the light pollution in your locality, visit the website: www.globe.gov/GaN/ where you will find instructions on how to observe the stars between 16 and 28 March and how to report your observations and get a report on the light pollution level in your locality.
Another major activity that is around the corner is the global project called 100 hours of astronomy from 2 to 5 April. During these 4 days (which mean about 100 hours) people all over the globe are expected to look through telescopes, hold discussions, ask question to astronomers, watch film on the development of astronomy in the 400 years since Galileo first looked at the planets, an event that we are celebrating during this International Year of Astronomy. We expect to hold stargazing sessions, discussions and film show on 3rd April in Dar es Salaam and Morogoro. Everyone with knowledge of the skies are expected to show and explain to those who are not familiar with the night skies. Visit www.100hoursofastronomy.org to get details of hundreds of events taking place around the world some with live web broadcasts including many telescope observatories.
During the International Year of Astronomy, good quality, cheap telescopes that are affordable for schools for use as teaching equipment are expected to be distributed. The telescopes are named Galileoscopes, in honour of Galileo, the scientific genius who was the first man to look at the skies using a telescope 400 years ago and began a scientific revolution in our understanding of the Universe. The Galileoscope has been specially designed to be of high quality, but manufactured extremly cheaply and are available for less than 30 dollars and as low as 15 US dollars each plus freight. They are also designed to be used as a school equipment to teach the physics of lenses and for use in astronomy. Schools are highly encouraged to use them since can be assembled and dismantled by students to provide a hands on learning. Visit www.galileoscope.org for a wealth of information about the Galileoscope.
In the night skies this month Venus bids us farewell by mid month with a last chance to view it in the glare of the setting sun. After that it will be too close to the sun and will move on to the morning skies. At the moment when viewed through a telescope it is a very thin cresescent which can be confused with the cresecent Moon. Saturn rises in the east by sunset so is visible throughout the night. Look for a piercing point of light best seen after 8 pm. Through a telescope it shows its rings edge on which is a unique position at the moment.
The Milky Way continues to dominate the overhead skies. In the early evening it cuts across the sky from the Southern Cross in the southeast horizon, up through Sirius (the Dog), between Orion (the Hunter) and Gemini (the Twins) in the overhead skies, descending to Taurus (the Bull) and ending in Perseus in the northwest horizon. Leo (the Lion) fills the eastern sky while the pointers Southern Cross in the south and Big Dipper in the north rise early in the west and can be used to find north-south direction after 9 p.m. Be careful not to confuse the False Cross with the real one!
The brightest star in the sky is Sirius and can be seen overhead at 8 p.m. The compact twinkling Pleiades star cluster, also known as Kilimia to Tanzanians can be seen on the northwest corner of Orion. The Moon will be close to this cluster on 30th March.
By the way, for a novice astronomer, it is best to start observing the sky in cities on a night with moonlight. This will allow the beginner to start by first recognizing the positions of the brightest stars and then gradually continue observing during moonless nights and relate these with the known brightest stars. Finally one can look for the fainter stars away from city lights and also observe star clusters and dust and gas clouds (nebulae).
March 20th is the day of Equinox when all over the world the length of day and night will be equal. It marks the change of seasons in northern and southern hemispheres on Earth.
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