Stardate:08:19:98
Welcome Back Jupiter
Larger than all the other planets in our solar
system combined, Jupiter returns this week to the southeastern sky. It
is low above the horizon, about ten degrees above, at 10 a.m. this week.
At that time, Jupiter will be 14 degrees south of due east. By 11 p.m.,
the icing of the planets will have moved to 25-1/2 degrees south of east,
at which time Jupiter will be slightly over 21 degrees above the horizon.
This mighty planet is shining at a very bright
magnitude -2.9. This makes it nearly six times brighter than the brightest
star in the night sky, Sirius.
Jupiter's four largest moons Io (pronounced Ee-oo), Callisto, Ganymede
and Europa are easily visible using any backyard telescope or pair of binoculars.
They are known as the Galilean moons, named after Galileo Galilli, who
discovered them in the year 1610.
Jupiter revolves around the Sun at a distance
ranging between 7,406,000 km (4,628,750 miles) and 8,160,000 km (5,100,000
miles). This is about 5 to 5.4 times further from the Sun than the Earth
revolves. Revolving around the Sun at over 13 km (8 miles) per second,
Jupiter completes an orbit once every 12 Earth years. Once every eleven
years, ten months, to be more exact.
The king of the planets could fit 1000 Earths
within it's mighty sphere. It has over 300 times the mass of the Earth.
Despite it's mighty mass, the tremendous diameter of Jupiter results in
a gravity of only 2.5 times that of Earth.
A day on Jupiter lasts less than 10 Earth hours.
This means that the rotational speed of Jupiter is over 26 times faster
than the Earth's. It's tremendous speed, combined with it's composition
create an obleteness, flattening Jupiter by over 6%.
When seen from Earth, only the cloud tops may
be viewed. Like Venus, Saturn Uranus and Neptune, the surface is forever
hidden from view. These bands often remind me of a large double cheeseburger,
particularly when I am viewing while hungry. The two brown bands are the
easiest to see across the diameter of this mighty planet. In addition to
these, there are numerous other bands of differing colors across it's otherwise
tan background. The Great Red Spot has faded quite a bit in the last few
years, but my childhood memories of it always reminded me of a small amount
of ketchup dripping out the side.
The atmosphere of Jupiter consists of large quantities
of hydrogen and helium which (with other molecules) formed methane, ammonia,
ethane, acetylene and other gases. The pressures at the center of Jupiter
are so great that hydrogen gas becomes a liquid just beneath it's cloud
layer, and may become a solid, metallic substance at Jupiter's core. Metallic
hydrogen is a strange, exotic substance which was only recently observed
on the Earth in a laboratory.
Jupiter produces the largest magnetic field in
the solar system, which (combined with the planets rotation) would kill
an unshielded human in an instant. This was first discovered by the two
Voyager spacecraft in the 1970's. It is 14 times more powerful than the
magnetic field of the Earth, and like the Earth, produces auroras at the
planet's magnetic poles.
Recent discoveries in the Jovian system include
active volcanoes on Io, discovered by Voyager I and 2, and likely liquid
water oceans on Europa, discovered by the Galileo spacecraft. The oceans
of Europa were foreseen by Arthur Clarke in his book 2010, first
published in 1982.
This mighty planet will delight amateur astronomers
for several months in it's gracefull dance across the sky.
Watch next week for a look at the strange moons
of this king of planets.
Clear skies, and good viewing.
Jim Maynard is the head of the astronomy department
at Earth Treasures and has been an amateur astronomer for more than 20
years. He is a physics student at Keene State College and leads star parties
at Wheelock Park in Keene, New Hampshire. If you have any questions about
astronomy or star gazing, call him at 603-352-7192.
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