Unit 4 Motions of Earth, Moon, and Sun

Apparent Motions of Celestial Objects Apparent Apparent motion is the motion an object appears to make. Can be real or an illusion. Stars Stars appear appear to move across the sky from east to west, however this is a result of the Earth’s rotation.

Daily Motion and Stars Most celestial objects appear to move across the sky from east to west. Most celestial objects appear to move across the sky from east to west. Vast majority are stars. Vast majority are stars. The paths of these celestial objects are circular, the polar constellations, or an arc. The paths of these celestial objects are circular, the polar constellations, or an arc. All motion is at a constant rate of 15 degrees per hour for a total of 360 degrees in 24 hours. All motion is at a constant rate of 15 degrees per hour for a total of 360 degrees in 24 hours.

Apparent Motions of the Planets Planet’s daily motion is similar to that of stars, however over a period of weeks or months the planets appear to change position with respect to the stars. Planet’s daily motion is similar to that of stars, however over a period of weeks or months the planets appear to change position with respect to the stars. This motion is not uniform. The planet will undergo the same motion from year to year but in different locations in the sky. This motion is not uniform. The planet will undergo the same motion from year to year but in different locations in the sky. The complicated motion is explained by the fact that all the planets rotate and revolve around the sun at different rates. The complicated motion is explained by the fact that all the planets rotate and revolve around the sun at different rates.

Apparent Motions of Earth’s Moon Follows daily east to west motion Follows daily east to west motion Rises 50 minutes later each day Rises 50 minutes later each day Shifts eastward each day compared to the background of the stars. Shifts eastward each day compared to the background of the stars.

Apparent motions of the Sun The sun also seems to move across the sky The sun also seems to move across the sky The path is in the shape of an arc The path is in the shape of an arc The path changes with the seasons The path changes with the seasons In the summer the days are the longest, the sun rises north of east and sets north of west, resulting in a longer arc In the summer the days are the longest, the sun rises north of east and sets north of west, resulting in a longer arc In the winter the days are shortest, the sun rises south of east and south of west, resulting in a shorter arc In the winter the days are shortest, the sun rises south of east and south of west, resulting in a shorter arc In the spring and fall days are almost equal, the sun rises due east and sets due west In the spring and fall days are almost equal, the sun rises due east and sets due west

Changes in the Sun’s Altitude Sun is always at its highest position at local solar noon Sun is always at its highest position at local solar noon Altitude depends on time of year and location of observer Altitude depends on time of year and location of observer Only between latitudes 23 ½ degrees N and S can the sun be observed directly overhead Only between latitudes 23 ½ degrees N and S can the sun be observed directly overhead

Models that Explain Apparent Motions Geocentric Models- Earth is the center of the solar system, Earth is stationary and everything revolves around it. (early cultures accepted this) Geocentric Models- Earth is the center of the solar system, Earth is stationary and everything revolves around it. (early cultures accepted this) - Explained the motions of the stars, sun, and moon, but not the planets. - Planets had orbits while they orbited Heliocentric Models- sun centered model Heliocentric Models- sun centered model - Earth rotates on its axis and orbits the sun - Daily motion of stars is explained by Earth’s rotation - Motions of the sun are explained by Earth’s tilt and revolution

Actual Earth Motions Moves Moves with the Milky Way as it expands Around Around the center of the galaxy once every 225 million years Rotates Rotates and revolves around the sun in an orbit

Rotation of Earth Tilted 23 ½ degrees from a line perpendicular to the plane of its orbit to the sun Tilted 23 ½ degrees from a line perpendicular to the plane of its orbit to the sun Axis remains at the same tilt the entire time it orbits the sun. Axis remains at the same tilt the entire time it orbits the sun. Rotates counterclockwise, from west to east Rotates counterclockwise, from west to east Satellites have proven Earth’s rotation Satellites have proven Earth’s rotation

Other Evidence of Earth’s Rotation Foucault pendulum- if allowed to swing freely the path will appear to change in a predictable way. If the Earth did not rotate the pendulum would maintain its original path. Foucault pendulum- if allowed to swing freely the path will appear to change in a predictable way. If the Earth did not rotate the pendulum would maintain its original path. Coriolis effect- merry-go-round example… Coriolis effect- merry-go-round example…

Evidence of Earth’s Revolution Around the Sun Earth’s change in distance does NOT cause the change in seasons Earth’s change in distance does NOT cause the change in seasons If Earth didn’t rotate around the sun the same part of the Earth would receive the more direct rays of sunlight If Earth didn’t rotate around the sun the same part of the Earth would receive the more direct rays of sunlight See different constellations at different times of the year See different constellations at different times of the year Sun appears to change slightly in size Sun appears to change slightly in size Slight changes in the Doppler effect Slight changes in the Doppler effect

Earth and Moon Motions and Time Throughout time people have used the motions of the Earth and moon as a frame of reference for time. Throughout time people have used the motions of the Earth and moon as a frame of reference for time. A month is determined by one cycle of the moon’s phases A month is determined by one cycle of the moon’s phases One day is determined by the rotation of the Earth One day is determined by the rotation of the Earth What determines the length of a year? What determines the length of a year?

Local Time Time based on the rotation of Earth as reflected in motions of the sun Time based on the rotation of Earth as reflected in motions of the sun All places on the same longitude have the same local time All places on the same longitude have the same local time If you move slightly east or west there will be different local times due to Earth’s rotation If you move slightly east or west there will be different local times due to Earth’s rotation

Local Solar Time For For any location the sun reaches its highest point once each day, solar noon. The The time it takes the Earth to rotate from solar noon to solar noon on two consecutive days is known as the solar day. This This type of time is known as solar time. Does Does a solar day have a constant length? Amean solar day has been established, divided into exactly 24 hrs.

Time Zones There is no limit to the amount of longitude lines that could exist. There is no limit to the amount of longitude lines that could exist. 24 time zones in 15 degree bands have been drawn 24 time zones in 15 degree bands have been drawn Each 15 degree segment has the same time Each 15 degree segment has the same time From one band to another is an increase or decrease of one hour From one band to another is an increase or decrease of one hour

Actual Motions of Earth’s Moon Revolves around the Earth in an elliptical orbit with a period of about 27 1/3 days Revolves around the Earth in an elliptical orbit with a period of about 27 1/3 days Half of the moon receives light at all times from the sun. Half of the moon receives light at all times from the sun. Phases of the moon are cyclic. It takes 29 ½ days from full moon to full moon Phases of the moon are cyclic. It takes 29 ½ days from full moon to full moon

Moon Phases New Moon - The Moon's unilluminated side is facing the Earth. The Moon is not visible (except during a solar eclipse). New Moon - The Moon's unilluminated side is facing the Earth. The Moon is not visible (except during a solar eclipse). Waxing Crescent - The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. Waxing Crescent - The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. First Quarter - One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. First Quarter - One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. Waxing Gibbous - The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. Waxing Gibbous - The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. Full Moon - The Moon's illuminated side is facing the Earth. The Moon appears to be completely illuminated by direct sunlight. Full Moon - The Moon's illuminated side is facing the Earth. The Moon appears to be completely illuminated by direct sunlight.

More Moon Phases Waning Gibbous - The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing. Waning Gibbous - The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing. Last Quarter - One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing. Last Quarter - One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing. Waning Crescent - The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing. Waning Crescent - The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing.

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Tides Cyclic Cyclic rise and fall of the oceans Caused Caused by the gravitation between the Earth, moon, and sun. There There is a bulge of water directly under the moon’s position. When When the sun, moon, and Earth are in a straight line, the sun enhances the tidal effect, and high tides are lower and low tides are higher.

Eclipses All opaque objects that do not give off their own light cast shadows in space. All opaque objects that do not give off their own light cast shadows in space. When another celestial object moves into a shadow of another object, there is an event called an eclipse. When another celestial object moves into a shadow of another object, there is an event called an eclipse.

Lunar Eclipse Occurs when the moon revolves into the shadow of Earth, at the full moon phase. Occurs when the moon revolves into the shadow of Earth, at the full moon phase. Averages to about 2 total lunar eclipses a year. Averages to about 2 total lunar eclipses a year. Partial eclipse occurs when only part of the Earth’s shadow covers the moon. Partial eclipse occurs when only part of the Earth’s shadow covers the moon.

Solar Eclipse Rare Rare The new moon can barely block out the sun. When this happens a shadow is cast on the Earth. The moon’s shadow can barely reach the Earth. The new moon can barely block out the sun. When this happens a shadow is cast on the Earth. The moon’s shadow can barely reach the Earth. A total eclipse can only be seen at any one location on Earth for up to 7 ½ minutes and once every 200 years. A total eclipse can only be seen at any one location on Earth for up to 7 ½ minutes and once every 200 years.