can see up to five planets in the sky with our naked
eyes. However, at any time, some of them might be too
close to the Sun for observation or they may be beneath
the horizon. The word planet originally meant "wanderer" because
ancient astronomers noticed that they moved compared
to the pattern of stars. The cover photo of the Star
Finder shows that movement. Venus is just above the
right horizon; Jupiter is 45° away beside "Eastern
Horizon." Six weeks later, they passed each other.
don't twinkle as much as stars because
they are discs rather than tiny points of light. Through
telescopes and good binoculars, you can see the disc
of many planets and the wonderful rings of Saturn.
In some years, the rings are tilted to us and easy
to see, at other times such as 2009, (and 1612 after
Galileo reported them) the rings are almost edge on
and hard to see. Mars is a tiny disc when it is on
the other side of the Solar System, but it appears
quite large when it is closest to the Earth at opposition,
such as in January 2010.
have flown by every planet and have landed on Venus and
Mars. Different missions will fly by dwarf planet Pluto
and orbit dwarf planet Ceres, both in 2015. Pluto was
demoted by the International Astronomy Union in 2006
because it's much smaller than every
other planet, and there are probably several other objects
bigger than Pluto in the outer reaches of the Solar System.
Solar System is mostly, but not exactly flat. Because
of that, the Sun, Moon, and planets all move through the
same region of sky. This is shown by the yellow band on
the Star Finder. It's labelled "Path of Planets," but
astronomers call it the "ecliptic" because
all eclipses occur there.
constellations on the Path of Planets are the signs of
the zodiac. Many of the ancient sky watchers
were really astrologers looking for relationships between
earthly and celestial events. Modern astronomers
have found no connection between our day to day lives
and the positions of solar system objects - unless
an object is found which might hit our planet.
Astronomy is science while astrology is a belief system.
have found many planets around other stars. Most
been found by measuring how stars move back and forth
as the unseen planets orbit their parent star. The most
massive planets are easiest to find by this technique,
but smaller and smaller exoplanets are being found. New
space missions will be sensitive to planets as small
as the Earth.
properties of the atmosphere of some Jupiter-sized exoplanets
have been determined from the way they reflect light
from their parent stars and how they interfere with that
starlight when they pass in front of the star. Very large
telescopes and new instruments currently planned may
be capable of obtaining infrared spectra of an Earth-like
planet. These spectra could be sensitive to the presence
of life on that planet. The first proof of life that
sprung up elsewhere in the Universe would be a momentous