Topic 4 EarthMoonSun Earths Rotation Causes daily changes

Topic 4 Earth-Moon-Sun

Earth’s Rotation – Causes daily changes • The spinning of earth on its AXIS – the imaginary line through the planet from the North Pole to the South Pole – is its rotation • The axis of the earth is tilted 23. 5° from a line perpendicular to the plane of its orbit of the sun.

Earth’s Rotation • As the earth revolves around the sun, Earth’s axis remains tilted at 23. 5° • The north end of the axis points toward the north star (Polaris) • Earth rotates 360° from west to east (counter clockwise looking down from the north pole) in 24 hours, at an angular rate of l 5° per hour (360°/24 hours = 15°/hour)

Tilt of the axis always stays the same – 23. 5° from a line perpendicular to the ecliptic plane

Evidence of Earth’s Revolution around the Sun • Seasonal Constellations: Because of the Sun’s annual motion, some constellations are visible at night only during certain seasons. • Constellations are visible when the dark side of Earth (away from sun) faces toward the constellation.

Zenith Position of the Sun • Because of the earth’s spherical shape, on any particular date, there is just 1 place where insolation (incoming solar radiation) is at an angle of 90°. All other places are less than 90°. • Does the 90° ever reach the United States? • An observer in New York State will never see the Sun directly overhead.

90° Perpendicular Rays of the Sun aka the ZENITH POSITION • The noon perpendicular rays of the sun travel southward from the Tropic of Cancer (23. 5° N) on June 21 passing the Equator on September 21 and going to the Tropic of Capricorn (23. 5° S) where it turns around and starts going back up passing the Equator on March 21 and arriving at the Tropic of Cancer again on June 21.

Seasons are caused by: The revolution of the Earth around the Sun The tilt of the Earth on its axis Parallelism of the Earth’s axis

Summer Solstice • On June 21 st , the Northern Hemisphere is tilted toward the Sun and the Tropic of Cancer is receiving the Sun’s vertical/direct ray which causes summer. • The Southern Hemisphere is tilted away from the Sun at this time causing it to have winter.

Winter Solstice • On December 21 st, the Southern Hemisphere is tilted toward the Sun so the Tropic of Capricorn gets the direct ray, giving them summer and us winter.

Equinoxes • On March 21 st and September 22 nd, neither hemisphere is tilted toward the Sun, the direct ray falls on the Equator, and every place on Earth has equal day and night.

The tilt of the Earth on its axis is also responsible for the day and night length: What date is it here? June 21 st What date is it here? December 21 st

Because of the tilt of the Earth’s axis, the sun’s rays are only perpendicular (directly overhead) at noon, between 23. 5° N and 23. 5° S during the year June 21 23. 5° N March/Sept. 21 Dec. 21 23. 5° S Tropic is from the Greek for "turning" describing the Sun's motion at the solstices.

• The locations of the Arctic and Antarctic Circles are determined by the positions of the Sun…the maximum distance from the Poles that can have 24 hours of daylight

“ALASKA MIDNIGHT SUN” NORTHERN HEMISPHERE FROM MARCH 21 UNTIL SEPTEMBER 21 – SUN DOES NOT SET TIMED PHOTOGRAPHY

The Sun’s apparent path is an arc that rises in the east and sets in the west, traveling 15 /hr and reaching its highest point at solar noon

Summer maximum altitude of noon sun is 73. 5°, Winter is 26. 5° Spring/Autumn?

Changing Altitude of the Noon Sun LONG ISLAND, NEW YORK

Sun’s path for our latitude

HIGHEST ALTITUDE AT SOLAR NOON AT 40° N

HOW DOES THE LOCATION OF SUNRISE AND SUNSET CHANGE DURING THE COURSE OF THE YEAR NO MATTER WHERE YOU ARE ON THE GLOBE, ON THE EQUINOXES THE SUN WILL ALWAYS RISE DUE EAST AND DUE WEST WHEN THE SUN TRAVELS NORTH OF THE EQUATOR TO THE TROPIC OF CANCER ON JUNE 21 ST (23. 5°N), THE SUNRISE AND SUNSET POSITIONS WILL MOVE NORTH OF EAST. WHEN THE SUN TRAVELS SOUTH OF THE EQUATOR ° TO THE TROPIC OF CAPRICORN ON DECEMBER 21 ST (23. 5°S), THE SUNRISE AND SUNSET POSITIONS WILL MOVE SOUTH OF EAST

Apparent Motion of Sun due to Rotation and Revolution • Rotation: Sun – apparent daily path from sunrise to sunset has the shape of an arc moving l 5° per hour. • Revolution: However, the sun’s arc changes both its position and its length with the seasons PROOF OF REVOLUTION – SEASONS

The apparent rising and setting of the sun is due to rotation Changes in the altitude of the path and horizon position of sunrise and sunset are due to revolution Season Sunrise Sunset Summer North of east west Equinox Fall/Spring Winter Due east Due West South of east South of west

EQUINOXES – DUE EAST

SUMMER SOLSTICE NORTH OF EAST

WINTER SOLSTICE SOUTH OF EAST

The Moon appears to rise in the east and set in the west, moving at a rate of 15 /hr, due to Earth’s rotation • However, the Moon is also orbiting Earth at a rate of 13 /day. Since it takes the Earth 50 minutes to “catch up” with the Moon’s orbit, the Moon rises 50 minutes later each day.

Moon Orbits the Earth – but appears to rise in the east and set in the west due to earth’s faster rotation

Moon’s Rotation = Moon Revolution Ø rotation period = 27. 3 days Ø revolution period = 27. 3 days Ø Moon shows the same “face” to the Earth Ø Velocity: 360°/27. 3 days = 13° per day

Moon Phases Ø Half of the moon is always receiving light from the sun. Ø The “lit” portion that is visible to earth varies as the moon REVOLVES around earth. THIS CAUSES THE PHASES OF THE MOON. Ø Visible portion of moon growing = waxing Ø Visible portion of moon shrinking = waning

Lunar Phases

Cycle of Lunar Phases Ø Takes 29. 53 days Ø This is because when moon gets back to its original position in 27. 3 days, the earth has moved 1°/day or about 27°. Ø The moon moving at l 3°/day takes about 2 days to catch up with Earth and align with it and the sun in a new moon phase.

What we observe from earth

Ocean Tides • An ocean tide refers to the cyclic rise and fall of seawater. Tides are caused by slight variations in gravitational attraction between the Earth and the moon and the sun. Tides are cyclic primarily because of the cyclical influence of the Earth's rotation. Moon 6. 2 million km. from Earth

• St. Michel, N. coast of France • ~16. 8 m highest tidal range in Nova Scotia

Nova Scotia Tides • Wolfville, NS (16 m tidal range) • Diurnal Tides (one high and one low every 12 hours and 25 minutes

Without the Moon, all the water on the Earth would be evenly distributed and we would not experience tides.

• The figure below shows how the position of the moon affects where high and low tides form.

Daily Cycle of Tides Ø Driven by the gravitational pull of the moon and Sun Ø Affected by nearness of the moon more than the size of the Sun Ø As earth rotates, the tides move around the Earth alternating between high and low tides approximately every 6 hours.

• Timing the Tides occur at different times each day because the Earth rotates more quickly than the moon revolves around the Earth.

• Bay of Fundy high – low tide • http: //www. youtube. com/watch? v=Yi. HP 8 E G_Wq 4

Spring Tides – Neap Tides Ø Tidal range: Difference in height between high tide and low tide Ø Spring Tides: new and full moon phase – greatest range Ø Neap Tides: 1 st and 3 rd Quarter phases – smallest range

Lunar and Solar Eclipses The Moon orbits the Earth, and travels with the Earth about the Sun. Sometimes the Moon gets between the Earth and the Sun, causing solar eclipses, and sometimes the Moon goes into the Earth's shadow, causing lunar eclipses.

Solar Eclipses – can occur only during the new moon phase Lunar eclipses – can occur only during the full moon phase

Solar Eclipses

Solar Eclipses Occur when moon’s orbit intersects ecliptic during the new moon phase

If Lunar eclipses happen in the full moon phase and solar eclipses happen in the new moon phase, why don’t they happen every month? ? ? As the Moon orbits the Earth, its orbit is tilted slightly (about 5 degrees) from earth’s orbital plane (ecliptic) The moon crosses earth’s plane twice during its orbit. If this crossing happens at the new moon phase, the Moon will be lined up with the Sun and pass in front of it. This alignment has to be perfect in order for the Moon to completely cover the Sun for a total solar eclipse (the sky will darken just like nighttime, and the stars will be visible) Total solar eclipses last about 7 minutes and occur in a very narrow range across Earth. Full moon phase = total lunar eclipse if perfect.

Total Solar Eclipses only last about 7 minutes in a very narrow range across Earth