APRIL NIGHT SKIES OVER TANZANIA

By Dr. N. T. Jiwaji

ntjiwaji@yahoo.com

Several planets light up the sky this month - so much so that an Air Canada pilot who had just woken up from a snooze mistook Venus as an airplane and hit the controls that took the plane into a steep dive injuring several passengers and crew.

Venus does indeed command attention since it is extremely bright at magnitude -4 and continues to brighten to its peak at the end of this month. Venus will catch the attention of even a casual observer since it looks like a spotlight only 30 degrees above the horizon at sunset.

Currently, Venus is fast approaching its closest distance to us of about 40 million kilometres at inferior conjunction. Hence, its apparent size is much larger and through even a small telescope, it shows a clear crescent shape because its orbit is inside that of Earth.

A remarkable sight will be presented on 24^th and 25^th April when we will be able to see two crescents in the sky – that of the Moon directly with naked eyes and that of Venus through a telescope. On 24^th the crescent Moon is at about 30 degree elevation above the western horizon at sunset, below Venus, while on 25^th it will have risen to about 40 degrees and will be above Venus (see picture)..

The closest approach to Earth by Venus on 6^th June 2012 has a special significance this year because Venus will pass directly in front of the Sun in an event called the “Transit of Venus”. In Tanzania we will see this event at sunrise, when it is nearing its end. For about two hours from sunrise until nearly 8 am, using special eclipse viewing glasses, we will be able to see a small dot of Venus near the edge of the Sun. During the two hours we will be able to see the dot move slowly as it crosses over the Sun’s edge. It is indeed like an eclipse because if the Moon was to come in front of the Sun, we would call that a solar eclipse.

While viewing Venus and Moon on 24^th and 25^th of this month, look closer to the horizon for the last view of Jupiter. It is about 10 degrees above the western horizon at sunset.

The “Jewel of the Solar System”, Saturn, is at its most magnificent having just passed opposition on April 15. At opposition, the full face of Saturn that is lit by the Sun is facing us. This year, its ring system is also sufficiently inclined to give us the most beautiful view through a telescope. At sunset, Saturn is close to the eastern horizon, so it crosses the sky during the night and sets in the west at sunrise. The best time to view it is when it is halfway up the sky, after 8 pm. You can locate it with naked eyes as a sharply shining unblinking light compared to nearby stars that will twinkle. Saturn is close to an equally bright star, Spica, the brightest star in Virgo constellation. You will see Spica twinkle noticeably while Saturn will steady. On 4^th May 2012, an almost full Moon will be close to Saturn.

Mars is also extremely bright, having passed opposition in March. Currently, it shines as a bright red star in the eastern sky, almost overhead at 8 pm, close to Regulus, the brightest star in the Leo constellation. Red Mars does not twinkle while Regulus will.

There is another red star that you can confuse with Mars. This is the red-giant star Betelgeuse in Orion constellation. It is in a similar position to that of Mars, but on the western side. It is also quite bright but not as much as Mars and its light will twinkle. A half Moon will be close to Mars on 30^th April and 1^st May.

So this month, you can see five of the six naked eye planets (including Earth!). Draw an imaginary line connecting the Sun, Jupiter, Venus, Mars, and Saturn and you will see that it is an almost straight line in the sky. This line is called the “ecliptic” and marks the plane of the solar system in the sky. Imagine that you are inside the flat plane that contains the planets and the Sun and are looking out towards the planets and the Sun. Then, you will be able to imagine, in your mind’s eye, the flat plane of the solar system while looking at the planets in the sky.

New Moon is on Saturday 21^st just after midnight, at which time an annular solar eclipse occurred on the other side of the earth from us, in the Pacific Ocean. First quarter will be on Sunday 29^th, when the Moon will be in half phase. This is the best time to view the Moon through a telescope or binoculars. Along the dividing line between the sunlit and night side of the Moon, its craters cast the long shadows that contrast to give a breathtaking view. Full Moon is on Sunday 6^th May. At this time, the Moon is lit full face from overhead by the Sun, and the craters become invisible due to lack of shadows.

In the sky (see the sky map) the prominent constellations of Orion, Taurus, Gemini and Sirius are all crowded in the western sky. The Milky Way, which contains these constellations, stretches from northwest to southeast. The easily recognizable Orion constellation will bid us farewell as it fades in the brightness of the western sky at sunset.

Leo takes centre stage in the sky, climbing high up in the eastern skies. This constellation has a distinctive curve of stars that looks like a backward question mark that forms the head of the lion. Its brightest star Regulus, close to which Mars appears this month, is in the neck of Leo. Regulus can also be identified as the dot in the question mark shape of Leo’s head. Regulus is a muliple star system, three of which have been directly observed and two these can be seen separated even in a small telescope or binoculars. Virgo enters the sky in the east, with Saturn close to its brightest star Spica. By 9 pm, Scorpio pops its three tentacle head over the eastern horizon and by 11 pm the glory of its full curving body can be seen in the east.

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 of the Big Dipper points towards the north. Be alert that the False Cross is also clearly visible and looks very much like the Southern Cross but bigger and points away from the south direction and has misled many a seafarer.

The International Space Station (ISS) can be best viewed on 7^th and 8^th May when it will cross the sky in the evening. On 7^th May it will rise above the northwest horizon at 7:25 pm and will slowly cross the western sky, becoming brilliant as it reaches a maximum height of 54 degrees. At 7:32 pm, before reaching the south horizon, it will suddenly disappear from view because it will have entered the Earth’s shadow. On 8^th May it will cross the whole of the northeastern sky after rising in the northwest soon after sunset at 6:30 pm. It will rise to a maximum of about 40 degrees, after which it will pass close to Saturn and disappear in the southeast horizon at 6:40 pm. For exact timings, check on the website www.heavens-above.com and enter the latitude and longitude of your location.

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