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Dr. Neal Sumerlin keeps us abreast of happenings in the night sky and the progress of the new Belk Astronomical Observatory.

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Saturn in 2009

Posted on 04/13/2009

Saturn has become more easily visible to the vast majority of people unwilling to get up after midnight to see him.  Shortly after dark, the second largest planet in our solar system is fairly high in the southern sky.  Here is a finder chart created for March, but which will still be good for mid-April.  Just shift everything a little to the west and it will work fine for 9 or 10 p.m.

http://transientsky.files.wordpress.com/2009/03/saturn_allsky_09452.png?w=455&h=297

http://transientsky.files.wordpress.com/2009/03/saturn_allsky_09452.png?w=455&h=297

Saturn is bright and somewhat yellowish in appearance.  It is already past opposition for this year, the point at which it is opposite the sun in our sky and therefore visible throughout the night.  The diagram below illustrates the relative positions of the sun, Earth, and Saturn at opposition in March, and at conjunction in September (when the sun and Saturn are conjoined from our point of view).

http://www.areavoices.com/astrobob/images/Saturn_opposition.jpg

http://www.areavoices.com/astrobob/images/Saturn_opposition.jpg

Saturn moves only slowly relative to the background stars because it is moving around the sun much more slowly than the Earth.  We lap it repeatedly, orbiting the sun almost 30 times for every one revolution by Saturn.  Last year at this time, Saturn was on one side of the constellation Leo; this year it is on the other side of the same constellation.  From the same source as the previous image (AstroBob, a superb astronomy blog to which I can only aspire, found here: http://www.areavoices.com/astrobob/), a diagram to illustrate:

http://www.areavoices.com/astrobob/images/Saturn_orbit_in_zodiac_1.jpg

http://www.areavoices.com/astrobob/images/Saturn_orbit_in_zodiac_1.jpg

Saturn's famous rings change their appearance during this 30-year cycle, also.  Right now they are tilted only slightly relative to us, but on September 4 of this year, they will disappear from view as they orient exactly edge-on.  This happens twice in every Saturnian year, every 14 or 15 of our years.  It is an illustration of the extreme thinness of the rings.  Made up of countless particles of ice ranging from 1 centimeter (0.4 inches) to 10 meters (33 feet) in diameter, they are broad enough to be seen over almost a billion miles of space, yet are probably only about 10 meters thick.  Imagine being an astronaut co-orbiting in these rings.  You would be moving around Saturn at the same speed as the particles, and could literally climb and "swim" your way from one side of them to the other.  What a spectacular view that would be!

Until then, we will content ourselves with this video taken by the Hubble Space Telescope of a rare transit of Saturn by four of its moons.  This only occurs when the rings are nearly edge-on, as the moons and the rings all orbit in the same equatorial plane.  When Saturn's rings are more highly tilted, the moons appear to pass above or below the face of the planet.  This link will let you choose the format and resolution that suits you best, and provides a brief explanation of what you are seeing: http://hubblesite.org/newscenter/archive/releases/2009/12/video/a/

 

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