Wednesday, 14 February 2007

Saturn Opposition 2007

Saturn is now in its period of apparent retrograde motion and achieved Opposition relative to the Sun on FEB 10 at 15 hr UT and its closest approach to Earth of 8.20035 AU.

Around the time of Opposition, Saturn is rising near sunset, transiting the southern meridian around local midnight, and setting near sunrise. Threfore, it is the most favourable moment to observe it. Its ecliptical latitude was N 1.3°, and its declination N 15.5°. That means for northern hemisphere observers, at meridian transit Saturn culminates at an altitude that is equivalent to one's co-latitude (90° minus one's geographic latitude) plus 15.5°.

At Opposition, Saturn's apparent equatorial angular diameter was 20.2 arcseconds and its rings covered 45.8 arcseconds. Its axial tilt relative to Earth was -13.9°. That means we will still be viewing the southern side of its rings, which orbit above its equator. The tilt will reach its extreme of -15.4° for this synodic cycle on APR 18. The extreme tilt for its 29.5-year orbital cycle came in 2003 at -27.0°. The rings will seem to disappear around the period when Earth moves through Saturn's equatorial/ring plane on 2009 SEP 04.

The previous section was taken from and the next section from

Observers who point a backyard telescope at Saturn (highly recommended) may notice that it doesn't look the same as it did last year. "The rings are tilting toward Earth," says amateur astronomer Alan Friedman of Buffalo, New York. He has been photographing Saturn for years and made this movie of his observations between 2004 and 2007:

"The Slow Dance of Saturn" by Alan Friedman using a 10-inch telescope.

The changing aspect is due to a combination of geometric factors, mainly the tilt of Saturn's spin axis plus the orbital motion of Earth. Eventually, the rings will narrow so much that they briefly disappear before opening up again. The next ring plane crossing: Sept. 4, 2009. Meanwhile, the rings are uncovering Saturn's blue north pole--one more reason to look through a telescope this time.