PLANETARY MOVEMENT
On any given night, the planets look stationary against the
background stars. But watch over a period of a few days for Venus or Mars and you can easily see why they are
called planets, from Greek, meaning wanderers.
Farther out, Jupiter and Jupiter and Saturn take longer for movement to
be noted, but move they do. Farther out yet are much slower moving
Uranus and Neptune, but even these slowly trace
their orbital courses against the stellar scene. Most of the times
the planets move directly, to the east through the
constellations of the Zodiac. But as our Earth laps the
slower-moving outer planets (or as the faster inner planets lap
us), they seem to stop and go backward into retrograde. Direct motion is shown below by Venus
and Mars and by Uranus, while retrograde is seen for both Jupiter
and Saturn.
Between March 9, 2004 (left) and just two days later, March 11,
2004 (right), Venus (at bottom) and Mars (below the Pleiades star cluster) move very
noticeably to the east against the stars of Aries and Taurus.
Jupiter moved some 10 degrees to the west in retrograde through Taurus
between October of 1988 (left) and January of 1989 (right) against
the background of the Hyades (bottom)
and Pleiades (upper left).
This pair of identically-exposed photographs also shows just how
much we have lost of the nighttime sky. The one on the left was
taken from town, the one on the right from a dark mountaintop. At
left, none of the faint stars can be seen.
The movements of Jupiter (the brightest body in the picture) and
Saturn (the bright one to the right of Jupiter) are easy to see
against the background of Taurus, both
close to the Hyades and the Pleiades. At left, on October 12,
2000, the planets have just begun retrograde; at right, February 16, 2001, they have already
resumed direct motion, but are still far west of their previous
position.
Between August 18, 2000 (left) and October 6, 2001 (right),
Uranus slowly moved easterly against the stars of
Capricornus.
Neptune, much farther away and fainter, is just visible at right.
Copyright © James B. Kaler.
