MARCH 2012 NIGHT SKIES OVER TANZANIA

MARCH 2012 NIGHT SKIES OVER TANZANIA

Though this month’s views of the night sky may be interrupted by clouds of the rainy season, it will be worthwhile to look through the gaps. Due to the variable climate we are experiencing, there can be even the occasional clear skies to exploit to watch the night skies.

Mars has just reached opposition and is at its bright red glow. Jupiter which is currently close to Venus in the western horizon is moving away and is due to leave our evening skies by mid-April. Brilliant Venus is set to brighten even more and has started its crescent view through a telescope. Saturn enters the evening sky by 9 pm now, and the planet is ready to show off its beautiful rings pattern through a telescope. All this is worth catching at this time..

We also need to prepare for the Global Astronomy Month marked during April with varied activities worldwide. Visit the website http://www.astronomerswithoutborders.org/global-astronomy-month-2012.html to follow many of the activities over the Internet.

April 11 to 20 will provide us with an opportunity to participate in the Globe at Night activity where the problem of light pollution and the need to preserve dark skies is highlighted. Go to their website http://www.globeatnight.org for guidance on how to measure sky darkness. You will be asked to count the stars that you can see from your area in the Orion constellation or the Southern Cross. If sufficient number of people from Tanzania participate, we will be able to show that world that Tanzania has very dark sky and show our potential for Astro-Tourism.

The month of March also ushers in the pointers that point out the poles. The South Pole can be located using the Southern Cross, which is up in the south east by 8 pm (see map). Early in the evening, the longer diagonal of the kite shaped constellation is parallel to the horizon. This is because we are 6 degrees south of the equator and the South Pole point in the sky is 6 degrees above the horizon. If you want to find the south direction you will have to wait a couple hours when the Southern Cross will have swiveled up and its longer diagonal can be extended to the south point in the horizon. In the north, the edge stars of the Big Dipper (see map) point towards the North Pole. To check if you have located the poles accurately, point one arm toward the north you located and point the other arm south. If you have located the two poles accurately your arms will be outstretched.

The Milky Way is a band of dense collection of stars, nebulae and interstellar dust that stretches across the March evening sky. It is marked by the Southern Cross, Canis Major (Big Dog), Orion, Taurus (Bull) and Perseus (see map). The Milky Way is actually a galaxy which is a huge collection of 100 billion stars. Our Sun is an average star among those billions. From earth we see the Milky Way as a narrow strip because we our galaxy is a flat, plate-shaped collection of stars. When we are looking at the band, we are observing the stars in our galaxy along its flat plane. If you turn your head away on either side of the band you see very few starts because you are watching the flat galaxy along its slender thickness. The true glory of the Milky Way can only appreciated away from the city lights where it becomes a truly milky band with distinctly fewer stars on either side.

Besides the myriads of stars, the Milky Way galaxy contains star clusters, and interstellar matter in diffuse nebulae. Young stars are continuously born within these nebulae due to the gravitational force which acts for billions of years over huge distances to pull together the wispy interstellar matter. Gravitational force also keeps together our Milky Way galaxy by pulling towards the massive black hole at the centre. The enormous system is 100,000 light years across (that would be the distance that would be covered in 100,000 years while traveling at the speed of light - 300,000 km per second). Until recently, our galaxy’s thickness was believed to be only a few thousand light years, but recent measurements show that it is actually 12,000 light years thick. All the galactic stars and material are contained in spiral arms, which rotate around the centre, making one revolution every 250 million years.

For observing bright stars and constellations, we in Tanzania are very well positioned to view the best of the southern skies because there is a far higher concentration of stars than in the north. Besides the Milky Way we can see the two brightest stars in the sky, Sirius and Canopus which you can locate using the star map. The constellation that is easiest to recognize is Orion with it huge rectangle taking up a large part of the over head sky around 8 pm. Once you have oriented the sky map with sky using these stars and constellations as pointers and the compass direction shown on the map, you will be able to follow the rest of the constellations and stars marked on the map. The middle part of Orion is an area known as the ‘sword of Orion’ contains the most beautiful collection bright interstellar dust or nebulae and even with the naked eyes you can see a patch of nebulous cloud one of them known as the ‘horse head nebula’. Of course you would need a telescope to make out such a horse shape.

There are plenty of deep sky objects that you can observe with the naked eyes. Among these is the Pleiades star cluster, also know as ‘seven little sisters’. It is an open cluster of newly formed stars embedded within bright interstellar matter where new stars are still forming. Another similar cluster is the Hyades cluster in Taurus Constellation near its red giant star Antares. An area close to the Southern Cross contains material which is not bright so we see a patch of darkness within a region of bright stars, hence its name the ‘coal sack’.

The Moon is ready to provide the most spectacular show in the evening 7 pm skies on March 25 and 26 when a thin crescent Moon comes close to Jupiter and Venus. On March 26 we will see a unique and beautiful arrangement in the western sky when the crescent Moon will be between Jupiter and Saturn. The moon is New on March 22 and Full on April 6 so the end of March will provide the best time to see its craters through the telescope when it is in half phase. The Moon will be close to Mars on April 3 when it will have a gibbous shape. An almost full Moon will be close to Saturn on April 7.