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What's Up In The Sky, March 2011

posted Feb 23, 2011, 8:00 AM by Marvin Stewart
              After this brutal winter it was wonderful to have a few warm days. Just to be able to sit outside and watch the glaciers in the yard retreat was uplifting. So this is an unscientific tribute to our local star, the Sun.
             Stars that dwell in the main sequence of the H. and R. diagram are a lot like soap bubbles. Their internal pressure is in balance with their external gravity. That gravity, created by their own mass, compressed them to create the internal heat and pressure that turned a swirling cloud of gas into a star. These two forces, pressure and gravity, meet at the boundary we call the photosphere. This is the point on the Sun where we cannot see any deeper, but heat and light can escape. But, there is no real surface, and to feel the same atmospheric pressure on the Sun that we feel here on Earth you would have to go tens of thousands of miles deep below the photosphere. It would be possible to fly a space craft through the Sun at this point, if it could be built to resist the intense heat. Although our Sun is stable enough for a planet with life to exist, it also has times when it isn't so calm.The calm periods are called solar minimums and they last about eleven years. During the eleven year cycle that we call a solar maximum, there are a lot of sunspot activity and masses of material are thrown off of its surface. In February of this year, after an extended period of calm,  a mass around eight times the size of the Earth was hurled into space. When masses of this size strikes Earth it produces a sustained electromagnetic pulse that can cause electric power grids to fail, damage satellites, disrupt radio and television communication and according to Donald Hamilton may be the source of comets. Since these cycles are predictable that also gives them sort of a stability.  Hamilton sees the maximums as glimpses of the Sun billions of years ago when it wasn't so stable. Back when as a young star it pulsed and violently  threw vast quantities of material, large and small, away from it in every direction. A lot of the material fell back into the Sun, some had enough speed to kept right on going back out into the galaxy. Some flew just far enough away from the the sun that when it fell back it went behind the fast moving Sun causing it to go into orbit around the Sun to eventually form a solar system of planets, moons, asteroids, and comets. The Sun has kept the speed of the cloud of gas it was formed from and is orbiting the center of our galaxy at 500,000 miles an hour. All the planets with their moons, asteroids, comets, and everything else in the solar system, orbit the Sun in a counterclock wise motion, approaching the Sun from the rear.
           If the Sun had been manufactured in Detroit, it might have been given a VIN number of G2 V dwarf. A mechanic servicing it could then tell it is a spectral class  G, yellow star, that isn't as hot as a 1, but hotter than a 3. The roman numeral V, its luminosity, places it near the middle of the main sequence with the other stars in the H. and R. diagram that arranges stars from blue hot to red not so hot.  It is a dwarf star and that is a good thing. Just as smaller automobiles are more economical with their fuel our Sun is also. Giant stars and super giants quickly burn up their hydrogen fuel and die. It is estimated that everything in the universe started out with 74 to 75 percent hydrogen and 24 to 23 percent helium. and around one to two percent of everything else. Assuming the Sun was no different and now after 4.5 billion years it has a helium content of 27 percent. Which means since its birth it has only converted 3 to 4 percent of its hydrogen fuel to helium. Unless mankind does itself in we will be able to enjoy our personal star a long, long, time.
            
         03  01    The crescent Moon is below and left of Venus in the dawn sky.
               04     New Moon.
               05     Mercury low on the western horizon at sunset.
               06     The Moon is to the right of Jupiter.
               12     First quarter Moon.
               13     Daylight saving time begins.  Really?
         13-16      Mercury, ascending, passes Jupiter descending in the western sky at dusk.Mercury will be about 10 deg. above the horizon for next 11 days.
               19     Full Moon.
               20     Spring comes to the northern hemisphere. The Moon will be near Spica all night.
               26     Last quarter Moon.
               31    Venus low and right of cresent Moon at dawn.
              
         
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