Determine How the Positions of the Sun, the Moon, and Earth Affect Moon Phases
What You Need to Know
A moon phase is one of the repeating shapes of the sunlit surface of the Moon as seen from Earth. A lunar month is the time between two successive and similar moon phases, which is about 29½ days. The waxing period of a lunar month is the time when the visible lighted surface of the Moon gets bigger. The waning period of a lunar month follows the waxing period and is the time when the visible lighted surface of the Moon gets smaller.
How Do Moon Phases Work?
The Moon's shape appears to change from day to day. These changes in the Moon's apparent shape are called moon phases. Phases are seen because the Moon orbits around Earth. Just as half of the Earth has daylight and the other half nighttime, half of the Moon is lit by the Sun while the other half is not. The phases of the Moon depend on how much of the sunlit half can be seen from Earth at any one time. The waxing moon phases are: new moon, crescent moon, first quarter moon, gibbous moon, full moon. The new moon is the phase when the side of the Moon facing Earth is not lit. The full moon is the phase when the side of the Moon facing Earth is fully lit.
Following the full moon, the Moon goes through the same phases in reverse. These phases are said to be waning (getting smaller). The phases in the waning period are full moon, gibbous moon, third quarter moon, and crescent moon. Then the cycle begins again with the new moon.
What Does This Have to Do with the Position of the Sun, Earth, and the Moon?
The position of the Moon relative to the Sun changes daily. When the Moon is between Earth and the Sun, we see a new moon. When the Moon is opposite the Sun and Earth is in between, we see a full moon. When the Moon is in between these two positions, different fractions of the lit side are seen.
A full moon occurs about 12.3 times each year. As a result, some months have two full moons. This occurs about every 2.75 years. The second full moon that occurs during one month is called a blue moon. The saying "once in a blue moon" means something that happens very seldom. About every 19 years, a year will have two blue moons.
Real-Life Science Challenge
Because only one side of the Moon faces Earth, does the Moon have what some people call a "dark side"? We see only one side of the Moon because it circles Earth in the same amount of time it takes to rotate on its axis. But while the same side always faces us, the Sun shines on all parts of the Moon's face at different times. The side of the Moon that we never see is more accurately called the "far side."
Now, start experimenting with a way to demonstrate the position of the Sun, the Moon, and Earth at different moon phases.
- Try using a light of some kind, such as a flashlight or a lamp, to represent the Sun.
- Use different-size Styrofoam balls to represent Earth and the Moon.
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