SEPTEMBER 1998
SEPTEMBER STAR MAP |
INDEX
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SEPTEMBER 6, 1998: Jupiter Rising
- The moon is full tonight, but more importantly, you will notice a bright
starlike object shining just to the left of the moon. Use binoculars to enhance
the view. Jupiter is making its appearance into the early evening sky. It now
rises almost due east about 7:50 p.m., but you should wait an hour or two so that
Jove can gain some altitude in the sky and be easily visible above distant trees
and rooftops. Jupiter is usually the fourth brightest object in the sky, followed
by Venus, the Moon, and the Sun. Its size and mass are staggering in contrast to
the other planets of our solar system. When compared to Earth, Jupiter is 318
times the mass (matter) of the Earth, over 11 times our diameter and 1300 times
our volume. It is the stereotype for the four outer worlds incorrectly known as
the gas giants. Although Jupiter, Saturn, Uranus, and Neptune have extensive
gaseous envelopes, their atmospheric pressures quickly liquefy their gases into
vast molecular seas of mostly hydrogen. Another misconception about Jupiter is
that one day it will turn into a star. No way! Although its composition is
mostly star stuff, hydrogen and helium, the internal pressures that are created
are far too small to initiate hydrogen fusion. For fusion to occur, add another
70-80 Jupiters into the pot, and you’d have the recipe for one very dim red star,
barely massive enough to sustain its own energy production.
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SEPTEMBER 13, 1998: Oppositon, Quadrature, Conjunction
- The changing positions of the planets and the Moon in the heavens result
from the various movements of Earth and the motion of the object under scrutiny.
Take for instance Jupiter, now gaining prominence in the evening sky. The
planet rises and sets due to the Earth’s rotation. It changes position against
the more distant background stars due to Earth’s orbital motion, as well as
Jupiter’s own revolution around the sun. We give special names to specific
angular distances of an object away from the sun. As an example, Jupiter
reaches opposition on Wednesday. It is opposite to the sun or 180 degrees
away from this star. Its rising and setting times will be in opposition to
the sun. So Jupiter will rise at sunset and set at sunrise. In other words,
Jupiter will be visible all night and highest in the sky at midnight
(1 a.m. EDT). When a planet is at an angle of only 90 degrees from the sun,
we term that location quadrature. The prefix quad means four. Four 90 degree
quadrants comprise a circle. When a planet and the sun are both viewed in the
same direction, the term conjunction (coming together) is coined. These same
elongations hold true for the Moon, but different words are applied. When
the Moon is in conjunction, it is new. When in opposition, it is full.
When the moon is at quadrature, it is either at first quarter phase or third
quarter phase depending upon whether the Moon is to the east or west of the sun.
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SEPTEMBER 20, 1998: Cartoon Moons
- One of my pet peeves has always been the incorrect representations of the
crescent moon drawn in cartoons. This week offers an excellent opportunity for
you to relate to this problem because the moon will be in this banana-shaped
phase all week. Starting about Tuesday, you’ll notice the thin crescent in the
southwest. As the week progresses, the moon will move towards the east, and
the crescent will continue to grow (wax). If you observe with a good amount
of twilight visible, it will be easy to witness that the crescent shape always
bows in the direction of the sun. In fact, the portion of the moon which is
reflecting sunlight will always tell you the most direct path to the sun. If
the thin crescent is visible in the morning hours, then it basically points
to the location of sunrise. In a cartoon, if the crescent is bowed towards
the lower right, it is an evening scene. If the crescent points towards the
lower left, it is a morning (before sunrise) time period. Look at cartoons
in The Morning Call, this week and you’re bound to see the crescent phase
incorrectly represented. The cartoon frame might show an evening activity,
like watching TV, but with a crescent moon outside the window that could
only be visible in the predawn sky. "It’s only a cartoon," you’re thinking.
Yes, but the misconception is reinforced so often that soon everyone is confused.
Don’t forget the autumnal equinox which occurs at 1:38 a.m. on Wednesday. Fall
is now upon us.
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SEPTEMBER 27, 1998: Moon Phases
- If you spent a little time glancing at the moon last week, you saw it emerge
as a waxing (growing) crescent to the east of the sun. Tomorrow, it will be at
first quarter, where the moon’s terminator, the demarcation between day and night,
will appear as a straight line. The moon will have completed one quarter of its
phases. Beyond that point, more than half of the lunar hemisphere facing us will
be lit by the sun. The moon will be in the waxing gibbous portion of its phases.
The terminator now bows outward, away from the illuminated limb. The full Harvest
Moon occurs on Monday, October 5th. Now the entire hemisphere facing us is bathed
in sunlight. After full moon the phases proceed in reverse, but now the amount of
illuminated surface is decreasing. Astronomers call this a waning moon. The moon
proceeds first through the waning gibbous phase, then third or last quarter moon
(Monday, October 12th), and finally the waning crescent phase, ending with the new
moon (Tuesday, October 20th). Here the far side of the moon, the portion which we
never get a chance to see, is illuminated. The hemisphere facing us is in darkness,
and thus the moon cannot be observed unless there is a solar eclipse. We have been
witness to a complete lunar day and night cycle. By our measure of time this takes
29.5 days, and it is from this period that we have derived our month (moonth).
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