27.3 – Sun-Earth-Moon System

Daily Motions Earth’s rotation causes us to see daily rising and setting of the Sun, Moon, and stars Rises in the East, sets in the West We observe changes in their location due to the Earth rotating

Day Length Solar day – time from one noon to the next noon Length of a day is approximately 4 minutes longer than it takes the Earth to make one rotation on its axis Foucault pendulum http://www.uni-heidelberg.de/university/museums/pendel.jpg

Earth orbits the sun in a slightly elliptical orbit Annual Motions Earth orbits the sun in a slightly elliptical orbit Plane of Earth’s orbit is called ecliptic plane This movement causes us to see different constellations in the sky during different times of year

Earth’s tilt The Earth’s axis is tilted 23.5° Axis remains fixed in space Cycle of seasons is due to this tilt When Northern hemisphere points towards the sun = Summer When Southern hemisphere points towards the sun = Summer

Solstices The Sun is overheard at its farthest distance either north or south of the equator

Summer Solstice around June 21st In Northern Hemisphere, number of daylight hours reaches its maximum Sun is in the sky continuously with the region of the Arctic Circle

Winter Solstice Around December 21st In Northern Hemisphere, number of daylight hours is at its minimum Sun does not appear in the region within the Arctic Circle

Equinox Equal nights Earth’s axis is perpendicular to the Sun’s rays and at noon the Sun is directly overhead at the equator Vernal – March 20, 2011 Autumn – Sept. 23, 2011

Phases of the Moon The moon does not produce its own light reflects light of the Sun The shape of the lighted portion of the moon, as seen from Earth, is known as its phases.

http://www.afreshhorizon.co.uk/images/moon_phases.jpg

Phases of the Moon New Moon = moon is between Earth & Sun So we do not see light reflected off of its surface Waxing = lighted area is increasing due to position between Earth & Sun Crescent = “sliver” of moon is visible 1st Quarter = ½ lit up Gibbous = almost Full

Crescent and gibbous moons

Phases of the Moon Full Moon Waning = decreasing amount of moon reflecting light due to position Gibbous 3rd Quarter = oppose half lit up after full moon Crescent New Moon

First quarter v’s last quarter moons

Earthshine Only during early crescent phases, “dark” part shines dimly, due to reflect light off the Earth

In-Class Assignment Start “Movements of Earth” WKT

27.3 Part B OBJECTIVES Describe the orbit of the Moon and its effects including cycles and eclipses. Illustrate how the Moon goes through phases..

Synchronous Rotation Moon rotates with a period equal to its orbit period Spins only once each time it goes around the Earth

Lunar Motions Lunar Month = complete cycle of phases from one New Moon to the next Rotation = 29.5 days Revolution of Moon = 27.3 days Orbits around Earth Moon rises and sets 50 minutes later each day

Tides Moon’s gravity pulls on Earth and creates bulges of ocean water As Earth rotates, bulges remain aligned with moon http://www.absoluteaxarquia.com/nightsky/images/tides.gif

Solar Eclipses Moon passes directly between Sun and Earth For more information see pg. 793 Moon passes directly between Sun and Earth Blocks sunlight Total eclipse only visible in small portion of Earth Partial eclipse is seen in larger portion

A series of photos of a solar eclipse!

A total solar eclipse!

A partial solar eclipse!

This solar eclipse shows flares (storms) on the edges of the sun!

Annular eclipses Eclipse with ring of the Sun visible Moon in apogee Due to the elliptical orbit of Moon causes it to be closer to Earth during parts of its orbit Perigee – closest point of Moon’s orbit to Earth Apogee – farthest point Moon appears smaller

An annular solar eclipse!

This is the difference between a perigee and apogee moon!

Lunar Eclipses Occurs with Moon passes through Earth’s shadow Earth is between Moon and Sun Moon faintly visible because Earth’s atmosphere is filtering sun light Lasts about 2 hours

Lunar eclipse – time elapsed pictures

Next eclipses

Time Zones Because of sun’s apparent motion, sun appears highest over different locations at different times World divided into 24 standard time zones In each zone, noon is when sun is highest over the center of that zone

Earth rotates 15 degrees every hour Time Zones Earth rotates 15 degrees every hour Each time zone is one hour earlier than the zone to its east International Date Line – point where earth changes from one day to the next

Daylight Savings Time Change your clocks November 7th at 2 AM Fall back an hour Spring forward an hour By changing your clocks, you gain an extra hour of daylight

Are calendars tied in with the moon? Day: time it takes Earth to make a full rotation Month: Time it takes the moon to go from through one cycle

Are calendars tied in with the moon? Year: Time needed for the earth to make one orbit (revolution) around the sun (365.25 days – makes us add a day every four years – leap year) The days of the week were named after the Sun, moon, and the five known planets.

In-class Assignment Finish “Movements of Earth” WKT