July NIGHT SKIES over Tanzania

By Dr. N. T. Jiwaji,

ntjiwaji@yahoo.com

A year from now on June 6^th there will provide us with a once in a lifetime experience that we need to prepare our people for.  The whole world, except for a few countries bordering the western shores of Africa and eastern shores of South America, will be able to see this event in one stage or the other.  The planet Venus will be seen from Earth crossing the face of the Sun.  The paths of the planets are confined in a thin flat plane hence once in a while they align in such a way that they are more or less aligned in a straight line.  We witness this commonly as eclipses of the Sun and the Moon.  However in the even that is to take place next year, Venus will pass exactly in front of the Sun.  Had it been the Moon that was in front of the Sun it would have covered up the face of the Sun entirely and have caused a solar eclipse.  However the size of Venus (i.e. the apparent size of Venus), as viewed from Earth is very tiny, nearly 2,000 times smaller than the apparent size of the Sun.  Hence as Venus crosses the face of the Sun, a small dark dot will be seen crossing the face of the Sun.

The spectacle is once in a lifetime occurrence because another such event will not occur for more than 100 years until December 11, 2117.  One might say that a transit of Venus occurred just seven years ago on June 8, 2004. This is true, but even that event occurred after more than a century after the last one that occurred on December 6, 1882.  In fact the frequency of transits of Venus occurs in pairs of close occurrences followed by more than century gaps.  After the transit that we will view next June 6, no human alive will have watched a transit until the next one occurs in 2117.  Is that not worth preparing for so that we can leave behind with our children and grandchildren legacies that can only be heard by word of mouth and books to their children and grandchildren!!

Transit of Venus gave human being the first opportunity to calculate directly the distance to the Sun.   The Earth-Sun distance provides an absolute scale of the Solar System using Kepler’s Third Law.  Though the distance could not be as accurately calculated as expected, due to atmospheric effects and diffraction, the first calculations using the transit of Venus provided a good value to understand the size and distances in our Solar System.

From Tanzania we will see the ending for the transit at sunrise of Wednesday June 6 2012.  We expect to see a dark dot just ready to exit from the edge of the bright Sun.  However, to enable us to see such a spectacle we need to be ready with special glasses that allow us to view it safely.  The full face of the Sun will be blindingly bright while the 2,000 times smaller dot will be hard to see unless we use the special glasses that will have to be purchased ready for use by that time.  Students can be educated on the science of the situation and the physics involved in explaining it and the math used to calculate the distance to the Sun.  We hope that over the coming months teachers will take every opportunity to raise this topic with their students who will in turn sensitize their parents about the unique event.

The close encounter in our night skies for the past few months of Saturn with the star Porrima in Virgo is playing itself out now with the sharply shining Saturn slowly sliding away from the star.  We only have a couple of months before our only planetary pal since March waves us goodbye.   Take the opportunity to view it in west close to the western horizon whence it will be lost in the glare of the sun by mid September.  By that time, Jupiter enters the late night skies and a moth later, Venus joins the show, both providing delectable spectacles worth waiting for.

The southern skies are filled with very bright stars that would be hard to hide!  The north and south direction pointers, that is the Big Dipper and the Southern Cross, are still high enough in the evening skies and can be used to mark the north-south direction very well.  Scorpius in the dominant constellation this month, occupying the overhead evening sky with its three stars forming its tentacles, the red star Antares in its neck and a long winding tail that ends in a close pair forming the sting.  Scorpius is the only constellation that does full justice to its namesake, the scorpion and is unmistakable to even a casual stargazer.  Below Scorpius, try to identify Sagittarius (the archer).  This constellation marks the direction of the center of our Milky Way galaxy and you will notice dense concentration of stars here.  The band marking the Milky Way contains numerous stars and dust patches and stretches from the southwest, passing through the Southern Cross and Sagittarius and upto Cygnus (the swan) in the northeast.  Leo (the lion) with its distinctive inverted question mark head is low in the western horizon and will be lost after this month.

Among the brightest stars noticeable in the July skies are: Alpha and Beta Centauri in the south form the pair that points continuously towards the Southern Cross; the fourth brightest star Arcturus is overhead towards the north and the fifth brightest star Vega rises in the northeast.  Other bright stars you will easily notice are Altair which rises in the east and Spica, the brightest star in the Virgo constellation can be seen almost overhead towards the west.