September Astronomyt Article and Sky Map for Tanzania

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abuali
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September Astronomyt Article and Sky Map for Tanzania

Postby abuali » 13 Sep 2010, 12:25

September Night Skies over Tanzania
By Dr. N. T. Jiwaji
ntjiwaji [at] yahoo.com

Astronomy is a silent participant in the background when millions of eyes are turned towards the skies, excitedly searching for a celestial body in anticipation of joyous celebrations. That was the mood last Thursday September 9th when the crescent Idd Moon could be clearly seen low in the skies among the gaps between the trees. The Sun’s glow was dimmed just enough by quarter to seven to allow Idd-crescent watchers to make out the golden bottom surface of the Moon, forming a beautiful golden crescent, hanging magically just 6 degrees above the still glowing horizon. Such a sight is rare since by the time the crescent is so low, it is in the clouds or dimmed by horizon haze in the glow of the setting sun.

The Idd-crescent is always a topic of discussion with a lot of uncertainty mixed-in. However, the New Moon (exact Sun-Moon alignment) on the afternoon of the previous day (Wednesday 8th) was just sufficient to allow the Moon to move away from the Sun by its daily shift of 12 degrees to be far enough and big enough the next day for the millions of Tanzanians to enjoy the view of the Idd-crescent, more than half an hour after sunset. However, the New Moon can occur at any time earlier than the afternoon. Then, by the next day, it is not sufficiently big or far enough away from the Sun to be visible and people have to wait yet another day for it to show itself. By the third day the crescent is quite big, and high enough above the sun to be white milky colour and not easy to make out a spherical shape for its surface.

Another recent event on Wednesday September 8th that most of us missed, but could have had huge consequence is the passage of two 20 to 30 meter asteroids that passed uncomfortably close to us, less than the distance to the Moon. This can look frightening but we have to live with the risk since only 90% of objects larger than 140 meters are detectable with the most sophisticated instruments that monitor these NEOs (Near Earth Objects). There are thousands of these objects close to us but the chances of them hitting us are extremely low. See more details at this website: http://szyzyg.arm.ac.uk/%7Espm/neo_map.html to get an impression about the issue.

Jupiter is seen as a huge star rising in the East soon after sunset when Venus is even brighter high in opposite western skies. Hence by 8 pm these two celestials are competing for attention and you would be forgiven for mistaking one for the other. This is a right time to take out your telescopes and fascinate others with the details that can be seen in the two planets. Jupiter has its four Galilean moons clearly visible all aligned in a line on either side of planet’s disk. Once in a while, one or two of them may play hide-and-seek when they go behind Jupiter as they orbit the planet. Parallel bands of clouds on Jupiter can also be just seen in a steady viewfinder when the air is settled. Jupiter’s Great Red Spot is also possible to make out in larger telescopes but you will have to time those since the spot rotates with the planet and is only visible when it is facing us directly.

On the opposite side, the western sky holds the jewel of the skies. Venus is now moving closer and closer to us, though in the process we see less and less of its bright face as the planet enters the area between the Earth and the Sun. Since we are now seeing more and more of the “night” side of the planet, the remaining bright part is seen as a crescent which is becoming larger and larger the closer it gets to us. You can easily make out the crescent shape in the telescope. By the beginning of next month on 10th October you will be able to see crescent Venus through a telescope while seeing the crescent Moon close by with your naked eyes. Plan for that day from now; it is a sight you should not miss.

This month’s unique event is the view the crescent Moon and Venus this Saturday on September 11th; a day when Americans will be remembering the tragic event of nine years ago. The crescent Moon will be beautifully positioned just one degree apart (one finger width held at an arm’s length) above and to the left of brilliant Venus. Mars appears as a dull reddish twinkling planet; bidding us goodbye until next year. It can be located about 6 degrees (a palm width) below and to the right of Venus; though you can’t see much details through even a modest telescope since it is very far from us. Do not confuse the bright star Spica which is also close to and below Mars. The more challenging view would be that of Saturn which only an experienced viewer will be able to see without the danger of damaging the eyes by accidentally looking at the Sun! SO BE VERY VERY CAREFUL.

The Moon is best viewed in a telescope when it is in its half disk phase which is called the “first quarter phase” since it is one quarter of its way in its orbit around the Earth. At this time the Sun casts the longest shadows of the craters on the Moon which we see in sharp contrast with the bright surface of the Moon. If you have a telescope, watch the Moon on the days close to September 15th. By September 22nd an almost full Moon rises just before Jupiter at sunset, while the next day the Full Moon rises just after Jupiter at sunset.

Stars are normally not much to enjoy through a telescope but this month you can enjoy one particular star called Epsilon-Lyrae which is close to Vega, a very bright star that can easily located in the north western skies about 40 degrees above the horizon (marked D on the sky map); look for the brightest star in that region of the sky. Just two or three finger widths away is Epsilon-Lyrae, which, through a telescope is a collection of FOUR stars. With a small telescope you can easily see it as a double star, but with a slightly bigger telescope, each of the two stars further resolve into two stars each, making up the quadruplet.

The Milky Way stretches as a band of numerous stars across the middle of the evening sky, passing through the Southern Cross in the southwest, through Sagittarius overhead, to Cygnus in the northeast. The portion of the Milky Way close to Sagittarius appears as a cloud that is not a real cloud but nebulae of dense interstellar matter that is hiding from our view a powerhouse that is a supermassive blackhole at the center of the Milky Way galaxy.

The Southern Cross which has been our constant companion for the past six month is now at the western edge of the southern skies with its long diagonal parallel to the horizon in the early evening. This shows that the South point that it points towards is 6 degrees up in the sky since we are at about latitude of 6 degrees. The pointers, made up by two bright stars Alpha- and Beta-Centauri point down vertically towards the Southern Cross. Alpha-Centauri is the upper star, is the closest star to us (after the Sun of course).

The Scorpio constellation can be clearly identified by its namesake the scorpion and can be seen high in the western sky. The eastern sky has two “birds”; one to the northeast, where you will see the Cygnus with its body and wings making a wide cross, while in the southeast you will see the smaller bird Grus with its head twisted sideways. Try to become familiar with the brightest stars by their names and relative locations. Enjoying the sky will not be as overwhelming as it might seem

23rd September is the day of Equinox when the length of day and night will be equal. The Sun shines directly above the Equator, and at local noon the Sun is directly overhead and you cannot see any shadow at that moment.

The best passes of the International Space Station which will allow you to enjoy the passage of this bright huge satellite passing brilliantly across the skies are on 21st and 23rd September. On 21st it will rise to 62 degrees after starting in the north-west horizon at 7 pm and crossing the whole sky and sets in the south-east at 7:04 pm.

On 22nd it will pass close to Venus around 7:29 pm after starting in the north-east horizon at 7:27 pm and moves close to the western horizon, setting in the south at 7:30 pm.

On 23rd, it will rise high in the sky up to 82 degrees, close to zenith. It will rise from the north-west horizon at 6:17 pm (just about sunset) and will cross high in the sky and will set at 6:23 pm. For more exact timing and details see this website:

http://heavens-above.com/

END
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Re: September Astronomyt Article and Sky Map for Tanzania

Postby abuali » 13 Sep 2010, 12:49

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