APRIL NIGHT SKIES OVER TANZANIA

By Dr. N. T. Jiwaji

ntjiwaji at yahoo.com

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With rains finally arriving to quench our thirst with a cooler climate, our stargazing plans will be rather unreliable this month. However, rains do have an advantage because they wash out the dust and smoke particles in the atmosphere. This will reduce the amount of light that is scattered (thrown) back towards hence we will have less light pollution. The skies are noticeably brilliant at the moment, so make use of breaks in the rain and clouds to go out to watch the stars, constellations and planets.

One of the first things to look for as soon as the sun sets is the pairing of Venus and Mercury in the western skies close to the horizon, among the light of the setting sun. As long as there are no clouds in the horizon, the glare of the sun is not as blinding due to cleaner air so these two planets are clearly visible together, about 4 degrees apart. You should be able to follow this pair for at least the next ten days, after which Mercury will be too low in the horizon. This is your best chance to see Mercury because the tiny planet rarely reaches the current highest altitude of 16 degrees above the glare of the setting sun.

Venus continues to rise in the western sky and reaches nearly 25 degrees by the end of the month; getting brighter every day. It will reach its highest altitude of 45 degrees by mid-August and will be our companion for another two months until October when it will be swallowed up in the shimmering sunset. For observers with telescopes it is very instructive to follow Venus during these seven months to see the changes in its shape (phase). It changes from full circle at the moment, to half phase when it is at its highest position in the sky. After that, as it drops back towards the horizon, its shape will change to crescent phase while its apparent size will increase threefold. In October when it is very close to the horizon, it will show up as a beautiful thin crescent that can easily be confused with the moon by someone who is just looking through a telescope.

The Moon is close to the Venus-Mercury pair on 15^th and 16^th April. On 15^th, Venus-Mercury-Moon will form a line with Venus at the top. The Moon will a very thin crescent below Mercury and may be difficult to observe since it is in the glare of the sun. However you can locate it by extending downwards the Venus-Mercury line. However on 16^th April, a thin crescent Moon will present an extremely beautiful sight when it comes close to Venus. Do not miss this sight. Moon is close to Mars on 22^nd while it comes close to Saturn on 25^th April.

Mars continues to be seen as a brilliant red star, and is currently seen overhead in the early evening skies. It has completed its retrograde (reverse) motion and has now resumed its normal shift from west to east across the background stars. Though a small telescope easily shows Mars as a disk, you will need a relatively high power telescope to see significant features on Mars.

Saturn is well above the horizon in the east, and though it is just a tiny point in the sky, it can be identified by its steady light that does not twinkle as compared to nearby stars that twinkle. It has begun its retrograde (reverse) motion shifting from east to west across the background stars, though this motion is very slight and not very noticeable since the planet is nine times farther away from us.

Saturn’s ring system has started to open up after being exactly aligned with our line of sight last year. This had caused the ring system to disappear from our view for several months but now that they are slightly inclined, we can seen them once again. At the moment the ring can be seen as a slim oval around the central globe. Watching Saturn through a telescope is one of the most beautiful sights that can be seen.

The prominent constellations of Orion, Taurus, Gemini and Sirius which we have been following since the beginning of the year are now crowded in the western sky. In an urban area, due to light pollution, the Milky Way can be made out as the path along which these constellations lie. It stretches from northwest to southeast and you will see far more stars along this band than in the rest of the sky.

The constellation that climbs high in the eastern skies is Leo (the Lion). At one end it has stars forming a distinctive curve in the shape of a backward question mark. This makes the head of the lion. The bright star Regulus at the bottom of Leo’s head is a triple star, two of which can be easily separated even through a pair of binoculars.

The direction pointers, the Southern Cross and the Big Dipper (shaped like an inverted sauce pan) are up in the sky and are visible throughout the night. The long diagonal of the Southern Cross points towards the south while the edge of the pan in the Big Dipper points north.

The International Space Station (ISS) will be best seen this month on 25^th and 26^th, moving across the sky from south west to north east on both days. On 25^th it will rise at 6:40 pm and will rise to a about 30 degrees above the south east skies, setting 6 minutes later. On 26^th April it will rise 7:04 pm and will rise to 30 degrees above the north west horizon taking 5 minutes to cross the sky. Happy viewing.

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