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What's up in the sky June '09

posted May 28, 2009, 2:51 PM by Marvin Stewart   [ updated May 28, 2009, 2:59 PM by James Roe ]

                 Galileo was puzzled, in 1610, when he had observed Saturn it appeared to have "ears".  But in 1612 they had vanished. No, they weren't the kind of ears we humans have, he was referring to something more like handles on a vase. Or, Galileo thought more likely Saturn had three bodies. Now they had disappeared. "Could it be as in mythology Saturn had swallowed his children?"  he wondered. Galileo didn't know his telescope wouldn't resolve the rings as a thin line. More puzzling to him was the following year,1613, the ears reappeared. This is a puzzle he wouldn't solve.
         The answer to this mystery would have to wait for a better telescope to be developed than the one Galileo had made.
          We now know  that periodically the Earth aligns with Saturn's ring plane, edge on, and they seem to disappear. Also, Saturn has four seasons. It is tilted on its axis 26.7degrees, or slightly more than Earth.  Since it takes Saturn 29 and 1/2 years, from an earthlings standpoint, to complete one orbit around the sun its seasons are much longer than ours. In Saturn winter and summer we view the rings from their top, or from underneath, but during its fall and spring we see the rings edge on. The rings were last edge on in1995. Since 1996 we have seen the underside of Saturn's rings and its southern hemisphere. In September of this year the rings will be at maximum edge on, and then we will slowly begin to get the top view again. This present alignment causes Saturn's southern hemisphere to be in the ring's shadow, and we can't  see the highly reflective rings. Distance also makes it dimmer. Saturn was at opposition in March so it is almost the furthest from Earth it can be and all these things add up to making it appear dimmer by about a magnitude.  No wonder Galileo was confused.
         In1655 Christann Huygens discovered that surrounding Saturn was a ring which he found to be solid and thin and nowhere touching. Another twenty years would pass before Giovanni Cassini would find the ring of Saturn to be made up of smaller rings with gaps between them. 
         This is your chance to see Saturn as Galileo saw it almost four hundred years ago, with the rings almost edge on. Modern telescopes can resolve the ring plane as a thin bright line. Don't miss it, if you do you are going to have to wait awhile.
 
          June 02  Near sunset look for the bright star Spica to the right of the crescent Moon.
                   05  Venus at greatest western elongation.
                   06  The 14 day old Moon occults Antares.
                   07   Full Moon 1:12p.m. CD.
                   09   Io and Ganymede's shadow visible on Jupiter before dawn.
                   14   Earliest sunrise for northern hemisphere,at 40deg, 4:31 a.m.
                   15   Last quarter Moon.
              19-21   The Moon is above Venus which is to the lower right of faint Mars at dawn.
                   20   The Moon is just less than a degree above the Pleiades at dawn.
                   21    Summer solstice.
                   22    New Moon.
                   26    Crescent Moon left of Regulus, near Saturn on the 27.
                   29    First quarter Moon.
                   30    At dusk the Moon is near the bright star Spica.
        

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