Rotating WondersRotating Wonders

Cyclical Phases of the MoonCyclical Phases of the Moon

Learning objectivesLearning objectives

How does the moon change shape in the How does the moon change shape in the sky? Why does it do this?sky? Why does it do this?

How is this related to the movement of the How is this related to the movement of the Earth?Earth?

Rotation of the EarthRotation of the Earth

The earth rotates The earth rotates counterclockwise counterclockwise while it orbits the while it orbits the sun. It takes the sun. It takes the Earth 1 day to spin Earth 1 day to spin about its own axisabout its own axis

www.blog.thesietch.org/.../2007/04/earth.jpg

Orbit of the MoonOrbit of the Moon

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

Orbit of the MoonOrbit of the Moon The moon orbits The moon orbits

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

Axis of Rotation

Rotation of the MoonRotation of the Moon

The moon also The moon also rotates about its rotates about its own axis in a own axis in a counterclockwise counterclockwise position. The time position. The time it takes the moon it takes the moon to rotate about its to rotate about its own axis is the own axis is the same time it same time it takes the moon takes the moon to orbit the Earthto orbit the Earth

Rotation of the MoonRotation of the Moon

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

Phases of the MoonPhases of the Moon

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

Major PhasesMajor Phases

There are four major phases of the moon:There are four major phases of the moon:

Full MoonFull MoonWaxing crescentWaxing crescentNew MoonNew MoonWaning CrescentWaning Crescent

Full MoonFull Moon

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

Waxing CrescentWaxing Crescent A waxing moon is a moon that A waxing moon is a moon that

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

New MoonNew Moon

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

Waning CrescentWaning Crescent A waning moon is a moon that A waning moon is a moon that

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

Period of RotationPeriod of Rotation

The phases of the moon occur about The phases of the moon occur about every 27.3 daysevery 27.3 days

This is equal to the time that it takes to This is equal to the time that it takes to rotate about the Earthrotate about the Earth

Phases of the moonPhases of the moon

http://csep10.phys.utk.edu/astr161/lect/time/phases.jpg

Rotation of Earth and MoonRotation 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 aboutThe 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.

VisualizationVisualization Imagine looking down on the Earth, Sun, and Imagine looking down on the Earth, Sun, and

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

VisualizationVisualizationIf the Moon rotates a quarter of the way around the Earth inRoughly 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 MoonSeasons and the Moon

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

VisualizationVisualization The Earth is tilted on its own axis, The Earth is tilted on its own axis,

so while it spins, different so while it spins, different hemispheres see the Moon in hemispheres see the Moon in different places. Imagine looking at different places. Imagine looking at the Earth-moon-Sun system from the Earth-moon-Sun system from the side:the side:

VisualizationVisualization

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

VisualizationVisualization As the Moon rotates around the Earth during the As the Moon rotates around the Earth during the

summer in the Northern Hemisphere, the moon summer in the Northern Hemisphere, the moon appears to move south in the sky.appears to move south in the sky.

VisualizationVisualization

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

VisualizationVisualization As the Moon rotates around the Earth during the As the Moon rotates around the Earth during the

summer in the Southern Hemisphere, the moon summer in the Southern Hemisphere, the moon appears to move north in the sky.appears to move north in the sky.

VisualizationVisualization

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

SummarySummary The Earth rotates counterclockwise about its own axis in a The Earth rotates counterclockwise about its own axis in a

day and the Moon orbits Earth’s axis in 27.3 daysday and the Moon orbits Earth’s axis in 27.3 days The Moon rotates counterclockwise about its own axis in The Moon rotates counterclockwise about its own axis in

27.3 days27.3 days We only see one side of the moon at all times because the 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 moon rotates about its own axis in the same time it rotates about the Earth.about the Earth.

There are four Major phases of the moon: New, Full, There are four Major phases of the moon: New, Full, Waxing, and WaningWaxing, and Waning

Each phase is caused by the position of the Earth and the Each phase is caused by the position of the Earth and the reflection of light from the Sun on the surface of the moonreflection of light from the Sun on the surface of the moon

The moon appears at different places in the sky during The moon appears at different places in the sky during different seasonsdifferent seasons

ReferencesReferences

PhysicalGeography.netPhysicalGeography.nethttp://library.thinkquest.org/http://library.thinkquest.org/http://csep10.phys.utk.eduhttp://csep10.phys.utk.eduhttp://nssdc.gsfc.nasa.govhttp://nssdc.gsfc.nasa.gov

Questions and DiscussionQuestions and Discussion