TWO BRIGHT PLANETS, WINTER 2015
Go outside the next clear night to look for two bright planets. You
don't need to know anything about astronomy to find them. As
twilight darkens the western sky, Venus glows brilliantly and simply
can't be missed. So lovely is its light that in ancient times it
was named for the goddess of love and beauty. For the next few months
it will continue to brighten. Near maximum it's easily visible in
daytime and in a dark location casts eerie shadows. Closer to the
Sun than Earth, as it orbits it goes through
phases like the Moon, showing different portions of
its day and nighttime sides. Discovered by Galileo around 1610, the
phases were instrumental in proving that Copernicus was right, that
the planets go around the Sun rather than the Earth.
On the other side of the sky, as darkness deepens, Jupiter rises high
in the east. Though not as bright as Venus, it overwhelms anything
else and is impossible to miss. Five time farther than Earth from
the Sun, the king of the gods takes a dozen years to go around the
sky against the background of the constellations of the Zodiac, residing in a different
one each year. Looking through his small telescope, Galileo found
four satellites that orbited in mere days, and drew the conclusion
that if Jupiter could control its moons then the Sun could control
its planets, again supporting Copernicus.
Venus and Jupiter could not be more different. Made of rock and iron
like Earth but just a bit smaller and less massive, Venus displays
a featureless cloudy surface. Not lovely at all, its clouds are made
of sulfuric acid floating in a dense atmosphere composed mostly of
carbon dioxide, the surface air pressure 100 times that on Earth.
With a greenhouse effect gone mad, the temperature on the ground
closes in on 900 degrees F. Radar observations show great numbers
of volcanoes, though we don't know if any are active. The planet
takes 243 days to rotate relative to the stars: backwards!
Jupiter is not a lot better. The largest planet in the solar system,
11 times Earth's diameter, 300 times Earth's mass, Jupiter is made
mostly of hydrogen and helium, much like the Sun. Floating in this
gaseous mix are clouds composed of ammonia and various hydrocarbons.
Not far below the apparent surface, under crushing gravity the
hydrogen turns liquid and then metallic. Rotating in just 10 hours,
the planet has a powerful magnetic field and lethal radiation belts.
Stretching out from the Jupiter are the four Galilean satellites,
which are bright enough to be seen in binoculars. Heated by tidal
stretching, Io, the size of our Moon, is the most volcanic body known.
Europa may have a deep underground ocean. Made mostly of ice,
Ganymede, the size of Mercury, is the solar system's biggest moon,
while similar Callisto is not much smaller. Go take a look, then
watch the planets change positions as the seasons progress.
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Copyright © James B. Kaler, all rights reserved.
These contents are the property of the author and may not be
reproduced in whole or in part without the author's consent
except in fair use for educational purposes. First published in
the January-March 2015 Clark-Lindsey Village Voice.