The Moon shines by reflected sunlight, therefore, only that portion of the Moon which faces the Sun is illuminated.
We see the illuminated portion of the Moon from various positions (aspects) during the month. The appearance of the Moon when seen from these various aspects account for the Moon's phases.
The Moon's period of rotation is approximately the same as its period of revolution. For this reason, we always have the same side of the Moon facing the Earth.
An eclipse of the Sun occurs when the Moon crosses in front of the Sun at the Moon's New Phase. An eclipse of the Moon occurs when the Moon passes into the shadow of the Earth at the Moon's Full Phase.
The Moon is the Earth's only natural satellite - a body that orbits around a larger body. Observations of the Moon and its changing phases have led mankind to the unit of time we call a month - the amount of time it takes the Moon to go through its phases. Next to the Sun the Moon is apparently the second brightest object in the sky. It can be seen during the daytime almost as often as it can be seen at night. The Moon is not the largest of the satellites traveling around the planets, but it does have a respectable size. Many superstitions have been and are still held about the Moon and its effects upon human beings, all of which have no basis in fact. But the Moon does have some profound effects upon the Earth. The Moon and the Sun together cause the Earth to undergo a little known motion called precession of the equinoxes. The Moon is directly responsible for the tides one experiences when one visits the beach. The tides, in turn, are a direct cause of the slowing down of the Earth's rotational rate.
Of all the information we have about the Moon, scientists are still frustrated about the Moon's origin. One hypothesis for the Moon's origin states that the Moon was a body in orbit around the Sun that came to close to the Earth and was captured by the Earth's gravity (the capture theory). In another, the Earth and Moon are twins forming side by side from the common cloud of dust and gas (the sister formation theory). A third hypothesis says that the Earth initially spun enormously faster than it does now and formed a bulge that ripped away from the Earth to become the Moon (the fission theory). The manned missions to explore the Moon from 1969 to 1972, provided new information about the material composing the Moon, but this only confused the issue more. Since this evidence does not support either of the three above theories, a new theory has been proposed. This new theory says that the Moon formed from debris blasted out of the Earth by the impact of a Mars-sized body. This occurred about 4.5 billion years ago after the Earth's core and mantle had been established. The colliding body melted and vaporized millions of cubic kilometers of the Earth's surface rocks and hurled this mass into space in an incandescent plume. This debris cooled, and gravity gradually drew it together into what we now see as the Moon. Regardless of its origin, however, astronomers concede that the Earth and Moon have a unique relationship in our solar system.
1. Upon what basis do we divide the year into months?
2. List some direct influences the Moon exerts upon the Earth?
3. Describe the currently accepted theory regarding the origin of the Moon.
4. Why would the Moon seem very large to an observer on Earth who compares its size with that of other visible celestial objects?
