Hobbies And Interests
Earth and Gravity
The moon is the earth's satellite, orbiting around our planet roughly every 28 days. Earth's gravity keeps the moon fixed on this path rather than spinning off into space. As the moon revolves on its orbit, it also rotates on its axis, in a similar way to the earth's own rotation which creates night and day. Since the moon takes as long to complete one full rotation as it does to orbit the earth, one side of it always remains unseen.
Sun
Although it appears bright in the night sky, the moon has no light of its own, it only reflects that of the sun. The part of the moon we call the dark side is not truly dark, it does receive sunlight, but that side is always turned away from earth. Depending on the relative positions of the sun, the earth and the moon, the moon may be illuminated as a full round circle, as a portion of a circle, or not at all.
Lunation
A complete cycle from new or dark moon to full moon and back again is called a lunation. A lunation equals one complete orbit around the earth. Our word "month" derives from the word "moon." The orbital path of the moon around the earth has an elliptical shape, so its distance from us does not remain consistent.
Phases -- Waxing
When the moon lines up between the earth and the sun, it seems invisible because only the side of the moon we do not see receives sunlight. This is its new or dark phase. Then the moon moves eastward in the sky, away from the sun, and we begin to see a thin crescent moon. The portion of the moon we can see grows larger each night, expanding from right to left, moving from crescent to first quarter to first quarter (half-moon) phase, then becoming what we call a gibbous moon. The period from dark moon to full moon is called the waxing moon period.
Phases -- Waning
When the moon is on the far side of the earth, away from the sun, the side of the moon visible from earth receives the sun's light. From earth we see a bright round disc -- the full moon. From here, the moon gradually appears to grow smaller in the sky as it moves toward the sun. Each night, darkness seems to eat away at the moon, making its roundness gradually disappear. Just as in the waxing phase, the light grows from right to left, so the darkness edges the moon in the same direction. The appearance of each of the moon's phases is reversed from the waxing period: first a waning gibbous moon, then a waning half-moon (called last quarter during the waning period), then a waning crescent. Then the moon becomes dark again and the cycle begins again.