Solar Motion

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MOTIONS OF THE EARTH

-DAY & NIGHT

Solar Motion

• Essential Question- Bell Ringer

• Why does the earth have day & night?

• Do other planets have day & night?

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• The Earth is a sphere (ball shape). Because of this only half can be lit by the sun at any one time.

Solar Motion• The earth spins (rotates) on its axis.

• The earth rotates in a counter-clockwise (west to east) direction

• It takes 24 hours for the earth to make one complete spin

Solar Motion• The half that is facing the sun, has light

(day)

• The half that is facing AWAY from the sun has NO light (night)

• Planets & moons that rotate also have day and night

Solar Motion

• Essential Question

• Why does the earth have seasons? Do other planets have seasons?

Solar Motion• Space objects are held in orbit by a force

called gravity (pull). Because of the pull of gravity between the sun and the planets, the planets follow a curved path (orbit) around the sun, instead of traveling in a straight line out into space.

Revolution

• The earth revolves (follows a path) around the sun.

• The path it follows is called an orbit.

Revolution

• Distance from the sun ONLY affects:– How long it takes for the planet to make

one complete trip around the sun (year)

• The farther away from the sun, the larger the orbit, the longer time it takes to make one complete trip around the sun

• Distance from sun does NOT affect temperature as long as we are in orbit

Solar MotionAs the earth moves around the sun in its orbit, the tilt of the axis stays the same.

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• As the earth moves in its orbit around the sun, the position of Earth in its revolution causes – Sometimes the northern axis is

leaning toward the sun, sometimes away, sometimes in between

Solar Motion– Sometimes the northern axis is leaning

away from the sun

– Sometimes the northern axis doesn’t lean either away or toward the sun

Solar MotionIf there was no tilt, the sun’s rays would not hit the earth’s surface so differently.

Note the differences in the places that have day.

No tilt to axis

23 degree tilt to axis

Solar MotionBecause the earth is a sphere and the

earth’s axis is tilted at about a 23 degree angle,– the sun’s rays do not hit earth’s

surface the same way if the northern axis is pointed toward the sun as it does when the northern axis is pointed away from the sun

Northern axis toward the sun

Northern axis away from the sun

Solar Motion

• When the northern axis is leaning towards the sun, the northern hemisphere gets the most direct rays

• Because of the position of earth in its revolution, days are longer so the earth has more time to absorb energy from the sun so the days are hotter.

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• When the northern axis is leaning away from the sun, the northern hemisphere gets the least direct rays

• Because of the position of earth in its revolution, days are shorter so the earth has less time to absorb energy from the sun so the days are cooler.

Solar Motion• The winter solstice is the shortest

day & longest night of the year. (December 21)

• At the opposite side of the orbit, is the summer solstice (the longest day and the shortest night of the year. June 21)

Solar Motion• At the positions in earth’s orbit

where the hours of day & night are equal, the northern axis is not leaning toward or away from the sun.

• These days are called equinoxes. The spring equinox is on March 21, the Fall equinox is on September 23

Solar Motion• The earth revolves in a counter-clockwise

motion around the sun.

• The days get longer between December and June.

• The days get shorter between June and Dec.

Solar Motion

Planets that have a slight tilt to their axis will also have seasons

Solar Motion

• Essential Question

• Why do the sun, moon, & stars APPEAR to rise in the east and set in the west?

Solar Motion• The earth rotates around its

action in a COUNTER-CLOCKWISE direction.

• This causes the sun, moon, & stars to APPEAR to rise in the East and set in the West.

• The earth is actually the one moving

Solar Motion•In the summer, the sun makes a shorter shadow at noon than in winter.

•This is because the sun is lower in the sky.

Solar Motion• The sun’s path across the sky is called

the ecliptic.• The sun follows a different path in each

season.

Solar Motion• In the Northern Hemisphere. the

sun’s path is higher in the sky in the summer.

• The sun follows a lower path (closer to the horizon) in the sky in the winter.

Solar Motion• In the Spring & Fall, the sun follows

a path that is higher than in winter, but lower than in summer.

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Summer

Winter

sunrise sunset

noon

Solar Motion

• Stars also seem to rise in the East and set in the West

Solar Motion• Stars that are above the North Pole

appear to rotate around the North Star

• This apparent motion is caused by the earth’s rotation

Solar Motion• An eclipse occurs when the sun, moon, &

earth line up.

• A solar eclipse occurs when the moon is between the sun & earth and the moon casts a shadow on the earth (blocks out the sun)

Solar Motion

• Total Solar Eclipse

Solar MotionA lunar eclipse occurs when the Earth

comes between the sun & moon. The shadow of the earth covers part or all of the moon.

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