UpDate - Vol. 11, No. 5, Page 5
October 3, 1991
Saturn: Visible tonaked eye in evening autumn sky

     Of the planets that are readily visible to the naked eye, only
Saturn now presents itself in the evening sky. The brightest
planets, Venus and Jupiter, are now in the morning sky, rising in
the east a few hours before the sun. Mars and Mercury are on the
other side of the sun this month, so it is only in the daytime,
when the sky is too bright for us to see them, that they are high
in our sky. Uranus, Neptune and Pluto are always too distant to be
seen with the naked eye (although sharp eyes at better sites may
sometimes discern Uranus among the faintest stars).
     When we look to Saturn, we see the most distant planet visible
without optical aid. Nearly 10 times farther from the sun than is
the Earth, Saturn moves very slowly against the background of
stars. It takes almost 30 years to complete one orbit of the sun.
Meanwhile Earth, zipping around the sun every year, has "lapped"
Saturn 28 times. Each time, we find the ringed planet only slightly
advanced along its celestial path. Thus, we may expect to see
Saturn once again next fall with its position shifted only a short
distance leftward from its present position at the western edge of
the constellation Capricornus. October, 1992, will find Saturn near
the center of that constellation.
     To see Saturn, face south and look approximately one-third of
the way up from the horizon toward the zenith; Saturn will be the
brightest starlike object in this vicinity. This is its position at
about 7:30 p.m. (EDT) in the middle of this month. If you look
later in the evening it will be to the right (west of south) and
lower in the sky until it sets at the western horizon about
midnight. This motion, of course, is just the result of the Earth's
rotation, causing all of the celestial sky to appear to make a
daily circuit around us from east to west.
     Above Saturn and, by 7:30 and later, somewhat to its right is
the star Altair, with a brightness similar to Saturn. Altair,
however, need not be confused with Saturn because, at this time, it
stands twice as high as the planet above the horizon. As seen from
Earth, the brightness of Saturn is comparable to the brightest
stars, however, several stars outshine it (including the summer's
brightest, Vega, which is still high overhead during October
evenings).
     On Oct. 16, the first-quarter moon passes Saturn. This happens
about dawn when both the moon and Saturn are out of sight below the
horizon. However, around this time, the moon can act as a marker to
help us locate Saturn. On the evening of Oct. 15, the moon will be
to the right (west) of Saturn in the sky by less than the distance
that your fist covers when held out at arm's length. By the
following evening (Oct. 16), the moon will have moved eastward to
stand at the left of Saturn as shown on the map. The map shows the
position of Saturn in relation to the moon and background stars at
9 p.m. on these two dates. Sizes of the moon and stars are made
disproportionately large on such maps in order to represent the
range of brightnesses.
     Halloween will find Saturn in essentially the same position
relative to the background stars, but that region of the sky will
be west of south by night and will have set by 10:30 p.m.
                                        - Richard B. Herr,
                    Associate Professor of Physics and Astronomy