Cyclical Phases of the Moon Rotating Wonders Cyclical Phases of the Moon

Learning objectives How does the moon change shape in the sky? Why does it do this? How is this related to the movement of the Earth?

Rotation of the Earth The earth rotates counterclockwise while it orbits the sun. It takes the Earth 1 day to spin about its own axis www.blog.thesietch.org/.../2007/04/earth.jpg

Orbit of the Moon The moon rotates about this same axis as well, but at a slower speed.

Orbit of the Moon The moon orbits around the Earth in a counterclockwise direction. It does this at a 5 degree tilt from the equator of the Earth. It takes the moon 27.3 days to orbit the entire Earth. Axis of Rotation

Rotation of the Moon The moon also rotates about its own axis in a counterclockwise position. The time it takes the moon to rotate about its own axis is the same time it takes the moon to orbit the Earth Here, the teacher might want to explain in greater detail just how the moon works by providing examples of objects or using the students to represent the earth and moon in an interactive activity.

Rotation of the Moon This is why we only see one side of the moon at all times during its orbit

Phases of the Moon Phases are caused by sunlight reflecting off the surface of the moon and also by the position of the moon relative to the sun and the Earth.

Major Phases There are four major phases of the moon: Full Moon Waxing crescent New Moon Waning Crescent

Full Moon When the moon is labeled a full moon, the face that we see is facing towards the sun.

Waxing Crescent A waxing moon is a moon that appears smaller every day until it becomes a new moon. This means the face we see is rotating away from the sun.

New Moon When the moon is labeled a new moon, the face that we see is facing away from the sun.

Waning Crescent A waning moon is a moon that appears larger every day until it becomes a full moon. This means the face we see is rotating towards the sun.

Period of Rotation The phases of the moon occur about every 27.3 days This is equal to the time that it takes to rotate about the Earth

Phases of the moon http://csep10.phys.utk.edu/astr161/lect/time/phases.jpg

Rotation of Earth and Moon Earth takes 1 day to rotate about its own axis and the moon takes 27.3 Days to orbit the earth. By the time that the moon has made one full orbit about The Earth, the Earth has rotated about 27 times. Because the moon and the Earth rotate at different speeds, the moon appears at different points in the sky each night and even sometimes during the day.

Visualization Imagine looking down on the Earth, Sun, and Moon system so that it becomes two-dimensional. the red dot represents one spot on the equator of the Earth. At this point, imagine the moon is in this position relative to the Earth and sun:

Visualization If the Moon rotates a quarter of the way around the Earth in Roughly 7 days, then the Earth has rotated approximately 7 times. instead of seeing the moon at night, you may see a waxing crescent during the morning.

Seasons and the Moon Similarly, the moon appears at different points in the sky during different seasons. This is because the moon stays in the same radial orbit, but the Earth “tilts”.

Visualization The Earth is tilted on its own axis, so while it spins, different hemispheres see the Moon in different places. Imagine looking at the Earth-moon-Sun system from the side:

Visualization The season affecting the Northern Hemisphere when the Earth is tilted away from the sun is winter, and the season affecting the Southern Hemisphere is summer.

Visualization As the Moon rotates around the Earth during the summer in the Northern Hemisphere, the moon appears to move south in the sky.

Visualization During winter in the Northern Hemisphere, the moon appears to move north in the sky.

Visualization As the Moon rotates around the Earth during the summer in the Southern Hemisphere, the moon appears to move north in the sky.

Visualization During winter in the Southern Hemisphere, the moon appears to move south in the sky.

Summary The Earth rotates counterclockwise about its own axis in a day and the Moon orbits Earth’s axis in 27.3 days The Moon rotates counterclockwise about its own axis in 27.3 days We only see one side of the moon at all times because the moon rotates about its own axis in the same time it rotates about the Earth. There are four Major phases of the moon: New, Full, Waxing, and Waning Each phase is caused by the position of the Earth and the reflection of light from the Sun on the surface of the moon The moon appears at different places in the sky during different seasons

References PhysicalGeography.net http://library.thinkquest.org/ http://csep10.phys.utk.edu http://nssdc.gsfc.nasa.gov

Questions and Discussion