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What's Up In The Sky July '09

posted Jun 24, 2009, 3:59 PM by Marvin Stewart
                       Lenox Lohr, the general manager of the 1933-'34 Chicago World's Fair, had to be nervous. He had came up with the idea of tying the 1893 Chicago World's Fair, "The Columbia Exposition" to "A Century of Progress Fair" which opened on May 27, 1933. Lohr had arranged for observatories around the country to point their telescopes at the bright star Arcturus, estimated to be 40 light years away. Those beams of light were focused on  photo-electric cells that would send an electrical signal over Western Union lines to the fair grounds. Then at the same exact time that President Cleveland had thrown a switch to turn on the fairs lights forty years earlier, the signal, created by light that had left Arcturus at that moment, forty years ago, would turn on the lights at the 424 acre site.  It worked.
               Arcturus, the brightest star in the northern hemisphere and the third brightest in the sky, as listed by recent surveys, is by modern measurement 36.7 light years away.
               From Earth every star we see is unique in some way, and near the top of that list is Arcturus. It is a spectral type K star, whose lives are measured in trillions of years, a very old orange giant, 26 times wider than the Sun. Arcturus has used up its hydrogen and is now burning helium. Its surface temperature is 4290 deg K, a lot cooler than the surface of the Sun.  It is one of 53 stars whose motion sets it apart. It isn't traveling with the rest of the stars in the arms of our galaxy, but is almost at a right angle to them. It is in a highly elliptical orbit about the center of of our galaxy in what is known as the halo. From our perspective Arcturus is diving down toward us and it is estimated it will be closest to us in just 4000 years. In time will disappear into the dusty arms of the Milky Way. Individual stars in the halo appear to move about the same speed as the Sun, but their motion is random. There is speculation, because of its motion, it is a star captured in a collision with another galaxy and retains the motion it had in that galaxy.  It could also just be an old halo star.
              Arcturus is also known as Job's star. It is the only star mentioned by name in the Bible, Job 9:9 and Job 32:38, this should give you some indication of how long mankind has been looking at the sky.  We find it in the constellation Bootes which we adopted from the Greeks. Other cultures recognized it too. To the Inuit's it was "The Old Man", the Polynesians called it "The Star of Joy" and they used it navigate their twin hull canoes, over open ocean from Tahiti to the Hawaiian Islands.
             To find Arcturus in the night sky find the Big Dipper and follow the curve of the handle in a gentle arc to the first bright star.
             Enjoy the stars of summer, they all have their stories.
             July   02   The mid point of the year occurs at noon UT.
                      03    The Earth is at aphelion, furthest from the Sun, 9PM CDT.
                      04    The Moon is less than a degree NNW from Antares.
                      07     Full Moon.
                 09-11        Jupiter is left of the Moon on the 9th and right of the Moon on the 10th. Neptune NNW of Mu Capricorni.
                      15     Last quarter Moon.
                 18-19    The Pleiades, Mars, Aldebaran and Venus in the dawn sky about 1 to 2 hours before sunrise.
                       21    New Moon.
             25-Aug1    Delta Aquarid meteor shower, strongest this week, early morning hours.
                       28    First quarter Moon.
                 30-31     Antares is left of waxing gibbus Moon on the 30th, and is right on the 31st. The Moon will occult Antares for
                               viewers in much of Asia and parts od Europe and Africa.