SEPTEMBER  1998

SEPTEMBER STAR MAP | INDEX

106    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.

107    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.

108    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.

109    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).