Download december 2012 astronomy

DECEMBER 2012 ASTRONOMY
From the Trackman Planetarium at Joliet Junior College
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The Winter Solstice, the beginning of winter, is on December 21st at 5:12 am (Central
Standard Time). On the Winter Solstice, the sun crosses the sky at the lowest trajectory
of the year. In the Chicago area, it doesn’t get higher than 25 degrees above the horizon.
At the Summer Solstice in June, the sun crosses the meridian, (directly south), 47
degrees higher than at the Winter Solstice. Because the sun is so low, the Winter
Solstice is the shortest day of the year. And since the sun is above the horizon for the
least number of hours at the solstice, we get the least amount of heat radiation from the
sun, and winter begins. South of the equator, the sun is in the northern sky and is
crossing at its highest point for the year and marks the beginning of summer in the
southern hemisphere.
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Although December 21st has the fewest hours of sunlight of any day of the year, the
earliest sunset is on December 8th. After December 8th the sun sets later each evening,
and by the end of December the sun is setting 11 minutes later than it does on the 8th.
The bad news is that it continues to rise later each morning until the first week in
January.
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Jupiter is the dominant planet in the evening sky and the only planet visible to the
naked eye. We will be at our closest approach to Jupiter on December 2nd when we will
be 377.5 million miles from the largest planet. Look for Jupiter in the eastern sky any
time after sunset. Mars is too close to the sun to be seen. Venus, Saturn and Mercury
are in the eastern sky just before sunrise. Mercury will be at its furthest west on
December 4th when it rises one hour and fifty minutes before the sun. Look for the
elusive Mercury below Venus.
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Orion is in the evening sky below Jupiter. The three stars that make up Orion’s belt are
easy to find. Below those stars is the Orion Nebula, a gas cloud that is material from old
stars coming together through a gravitational force called accretion to form new solar
systems. The Orion Nebula is a great binocular target. The red star that marks Orion’s
shoulder is Betelgeuse. Betelgeuse is red because it is cooling down and about to go
supernova - some time in the next million years or so. As an example of a “hot” blue
star, look at Rigel which marks Orion’s foot - to the right as we see it. The bright star
above Orion and Jupiter is Capella in the constellation of Auriga. Capella is the sixth
brightest star as seen from Earth, Rigel is the seventh brightest, and if you follow
Orion’s belt to the east, you will find Sirius - the brightest star as seen from Earth. To
the right of Jupiter is the Pleiades, a group of stars that formed just a few million years
ago. The Pleiades is another good telescope target. If you drive a Subaru, the Pleiades
is your hood ornament. The Pleiades mark the shoulder of Taurus the Bull. The red star
in Taurus (below Jupiter) is Aldebaran. The “W” of stars that form Cassiopeia are high
above at mid-evening. Below them is the Andromeda galaxy. Gemini is above and
slightly east of Orion. The two bright stars that mark the heads of the Gemini twins are
Castor and Pollux.
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The Geminids Meteor Shower is on December 13th. There is a new moon that evening
so the moon won’t interfere with meteor watching. In the late evening, look in the area
above Orion for the Geminids Meteor Shower.
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The full moon in December is on December 28th. This full moon is called the “Full Cold
Moon”. Since the full moon is opposite the sun, the full moon in December crosses as
high in the sky as the summer sun.
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th
On December 30 , Pluto will be at its furthest from the Earth for the year - slightly over
3 billion miles.
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The world will not come to an end on December 21st. The Mayans never said it would.
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December 14th will be the 40th anniversary of the last man on the moon. On this date in
1972, Astronaut Eugene Cernan stepped into the Apollo 17 landing module to return to
Earth. Apollo 17 was also the last time man has been above Earth orbit. The Chinese
Lunar Exploration Program (CLEP) is expected to put a man (or woman) on the moon
around 2025.
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The free public shows at the Trackman Planetarium are “Colliding Objects in Space” on
December 4th at 7:30 pm; “The Christmas Star” on December 16th at 2:30 pm (this is a
Sunday show); and “The Christmas Star” on December 18th at 7:30 pm.
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As stated above, December 21 marks the beginning of winter and the lowest the sun
will cross the sky this year. Since June, the sun has appeared lower in the sky each day.
This change in the sun’s trajectory across the sky is the result of Earth’s axis being on a
23.5 degree tilt from our orbit around the sun. A globe’s axis is normally set at the same
angle as the Earth‘s axis. For thousands of years, throughout the northern hemisphere,
ancient man watched the sun get lower in the sky each day and worried that it would
disappear below the horizon. When the sun seemed to stop (solstice means “stop”) and
then started crossing higher in the sky, they celebrated. They built structures such as
Stonehenge in England, Newgrange in Ireland, Denghood in Germany, and the
medicine wheels of the Native Americans to mark the solstice. Almost all of the
cultures had solstice celebrations dealing with lights and with gift giving. Our
decorated trees, wreaths, mistletoe, gift giving, Yule logs, etc. are carryovers from these
celebrations. In 336 A.D., Constantine declared that Christians should celebrate the
feast of the Nativity at this time, adding Christmas to the holiday. (Earlier Christians
had celebrated it in the spring.) The Jewish feast of Hanukkah (lighting of the
Menorah) predated Constantine by several thousand years. With that long and diverse
history in mind, we wish you the best of the season, and hope you have a great
Christmas, Yule, Saturnalia, Hanukkah, Maslenitsa, Diwali, Chaharshanbe-Suri,
Kwanzaa, “We-Just-Maxed-The-Cards Day” or whatever you want to celebrate, and we
also wish you a warm and gifted new year.
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Art Maurer
Director -Trackman Planetarium
Joliet Junior College
([email protected])