Download September 2013 - Joliet Junior College

SEPTEMBER 2013 ASTRONOMY
From the Trackman Planetarium at Joliet Junior College
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The Autumnal Equinox is at 3:44 pm on September 22nd. It is the end of
astronomical summer and the beginning of fall. On that date, the sun is directly
above the equator and will continue to move southward over the southern
hemisphere to 23 degrees below the equator. Here in the Midwest, it means the
sun will cross the sky at a maximum 48 degrees above the horizon on the 22nd.
The sun crosses at a maximum 71 degrees above the horizon in the summer and
25 degrees above the horizon in the winter. On the Autumnal Equinox the sun
rises directly to the east and sets directly to the west. On the equinox, the sun is
above the horizon for 12 hours and below the horizon for 12 hours; after the
equinox, the farther north you go, the fewer minutes of sun you get each day.
(The opposite has been true all summer.) At the north pole the sun sets at the
equinox and will not rise again until spring. Since the sun is crossing the sky
lower each day during September, we lose one hour and nineteen minutes of
sunlight. The Earth’s orbit is taking us closer to the sun each day - we are closest
to the sun in January - and so we are orbiting faster during the winter than in
summer. There are 7 fewer days between the first day of fall and the first day of
spring, than between the first day of spring and first day of fall. Seven more
days of summer than winter!
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Saturn and Venus are low in the western sky after sunset. On September 20th,
Venus will appear less than 4 degrees below Saturn. Saturn appears as a yellow
star. Venus is so bright you can’t miss it. Venus will continue to move eastward
across the sky until December. Saturn will move across the sky to the west until
it crosses behind the sun the first week in November. Mercury is setting after the
sun, but is very low in the sky. Jupiter and Mars are in the early morning sky
before sunrise. Jupiter will be in the evening sky starting in November.
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The three stars that makeup the Summer Triangle are directly above at midevening and the Milky Way runs between them. Cassiopeia is above the
Summer Triangle and looks like a “W” of stars. The Milky Way runs from
Cassiopeia through the Triangle down to Sagittarius at the horizon. Sagittarius
looks like a teapot. Below Cassiopeia and slightly to the left is the square of
Pegasus. Above Pegasus is the Andromeda Galaxy, the closest major galaxy to
our Milky Way Galaxy. In clear, dark skies, the Andromeda Galaxy is visible to
the naked eye - it is the farthest object visible to the naked eye. Without dark
skies you need a pair of binoculars to find it.
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Like Earth, the sun has magnetic poles. The magnetic poles on the sun are about
to reverse. They reverse every 5½ years at the solar max - the time when we have
the most sunspots. Although we have had very few sunspots during this cycle,
the pole reversal on the sun has already started. The reversal will have no
consequences for people on Earth. The magnetic poles on Earth reverse on an
average of every 450,000 years and it takes between a thousand and ten thousand
years for them to switch.
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The full moon is on September 19th and it is the Harvest Moon. It is known as the
Harvest Moon because before tractors had headlights, farmers used the moon for
light when they harvested their crops. The full moon in September is a cause for
celebration in many Asian cultures. Children receive treats for having worked in
the fields all summer. A special treat is a Mooncake (They’re good!) and the
launching of sky lanterns - which are illegal in Illinois.
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The Public Shows have resumed at the Trackman Planetarium. The shows for
this month are “Seasonal Skies” on September 3rd at 7:30 pm and on September
12th at 6:30 pm; and “The Solar System” on September 17th at 7:30 pm and on
September 26th at 6:30 pm. We are taking reservations for special programs for
school and scout groups. Contact the Office of Resource Development at (815)
280-2328 or [email protected].
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A nova has been discovered in the constellation Delphinus. Delphinus is next to
the Summer Triangle. Nova Delphini 2013 was discovered on August 14th and
has brightened to be visible to the naked eye in dark skies. Although “Nova”
means “new”, a nova is a nuclear explosion in an existing white dwarf star which
has accreted so much hydrogen from a companion star that it starts nuclear
fusion. With a pair of binoculars, Nova Delphini will look like a very bright star.
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Super comet Ison, which is due here at Thanksgiving time, has lost a lot of its
luster. Once expected to be brighter than the moon, Ison is not growing as
expected. It will still be a visible comet in the early morning sky in November,
but not nearly as bright as once expected.
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Art Maurer
Director -Trackman Planetarium
Joliet Junior College
([email protected])