by Jim Maynard
Star date: 07:20:97
Jupiter is set to attract attention in the skies
through the summer months. The largest of the Sun's nine planets, Jupiter
is also the second brightest of the planets. It's no wonder that the ancients
worldwide named it after their respective king of the Gods. As the planets
moved against the background of the so-called "stationary" stars,
people worldwide attributed them with magical powers. They were soon promoted
to Gods.
Jupiter is larger and has more mass than all the other planets combined. It also has a radiation belt spinning around it strong enough to kill a human instantly.
Early in the 17th century, Galileo Galili became the first person to do a systematic study of the heavens. He is often falsely credited with the discovery of the telescope. This is not true, although he may have nothing to extinguish that idea. He was also not the first person to point a telescope to the sky, but he was, almost certainly, the first person to write down what he saw. The telescope, in fact, was a Dutch invention, designed to spot ships in the distance coming into a port. As if this were not enough, the idea was stolen from the Arabs (who at this time were the keepers of the knowledge of ancient Greece and Alexandria, which had been forgotten in Europe). It seems highly unlikely the Arabs were using lenses to spot ships in the distance. Maybe camels. Galileo, however, was an intensely curious character, and he set about a systematic study of the universe in which we live.
One of the first objects Galileo turned his gaze
to was the bright king of the planets, Jupiter. It was here he came across
one of the most stunning findings in science at the time. He could see what
appeared to be four stars near Jupiter. When he looked again on successive
nights, the same four "Stars" were still near Jupiter, but in
different positions. Over the course of time, it dawned on Galileo what
he must be seeing. What he at first mistook for stars had to be moons circling
the massive planet. This fact, which seems so simple and obvious today,
had Earth shaking consequences. At the time, people were undecided between
the Ptolemaic (Earth centered, or "geocentric") universe, and
the Copernican (Sun centered, or "heliocentric") universe. Of
course, we know today that neither one is correct, for the universe is not
centered on either the Earth or the Sun. In fact, it has no center. But
for the solar system anyway, Copernicus was correct. Galileo's discovery
of four moons of Jupiter (the first moons known, other than our Moon) proved
that not everything was circling around the Earth, after all, these four
objects were clearly circling around Jupiter. Of course, the geocentric
theory lived a short while longer under the premise that "The Jovian
moons may be going around Jupiter, but that means they are going around
the Earth with Jupiter ". This was, however, the first one of the blows
which would soon kill the idea of an Earth centered universe.
Later, when it was noticed that the moons of Jupiter (there are nearly 20 known so far) did not seem to obey the laws of orbital mechanics developed by Isaac Newton and Johannes Kepler, a remarkable idea sprung forth; that the moons were obeying the laws of orbital mechanics, but that the speed of light was finite. This lead to the first measurement of the speed of light. It wasn't very accurate, but it was in the right ballpark.
Also, keep your eyes open for the Southern Data Aquarid meteor shower, peaking in the pre-dawn sky on the night of July 27/28, towards the constellation Aquarius, almost due south at 3 am.
Clear skies, and good viewing.
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