Ch 23Ch 23 Section ISection I

The EarthThe Earth

Earth is now known to be a round Earth is now known to be a round 3-dimensional sphere3-dimensional sphere

Axis – imaginary vertical line Axis – imaginary vertical line around which earth spinsaround which earth spins

Rotation – the spinning of Earth Rotation – the spinning of Earth around its axis that causes day and around its axis that causes day and

nightnight

Earth has a magnetic field with Earth has a magnetic field with north and south polesnorth and south poles

Cause of seasonsCause of seasons

Revolution – Earth’s Revolution – Earth’s yearly orbit around yearly orbit around the sunthe sun

Earth’s orbit is an ellipse. or Earth’s orbit is an ellipse. or elongated, closed curveelongated, closed curve

Because the Sun is not centered in the Because the Sun is not centered in the ellipse, the distance between Earth and ellipse, the distance between Earth and the Sun changes during the yearthe Sun changes during the year

Earth’s tilt causes the seasonsEarth’s tilt causes the seasons

The hemisphere tilted toward the The hemisphere tilted toward the Sun receives more daylightSun receives more daylight

The longer period of sunlight is one The longer period of sunlight is one reason summer is warmer than reason summer is warmer than

winter.winter.

Earth’s tilt causes the Sun’s Earth’s tilt causes the Sun’s radiation to strike the hemisphere radiation to strike the hemisphere

at different angles at different angles

The hemisphere tilted toward the Sun The hemisphere tilted toward the Sun receives more total solar radiation than the receives more total solar radiation than the hemisphere tilted away from the sunhemisphere tilted away from the sun

SolsticeSolstice the day when the sun reaches its greatest the day when the sun reaches its greatest

distance north or south of the equatordistance north or south of the equatorSummer solstice occurs June 21 or 22 in Summer solstice occurs June 21 or 22 in

the northern hemispherethe northern hemisphereWinter solstice occurs December 21 or 22 Winter solstice occurs December 21 or 22

in the northern hemispherein the northern hemisphere

EquinoxEquinox the day when the sun is the day when the sun is directly over Earth’s equatordirectly over Earth’s equator

Daytime and nighttime hours Daytime and nighttime hours are equal all over the worldare equal all over the world

Spring equinox occurs on March 20 or 21 in the Spring equinox occurs on March 20 or 21 in the northern hemispherenorthern hemisphere

Fall / Autumnal equinox occurs on September Fall / Autumnal equinox occurs on September 22 or 23 in the northern hemisphere22 or 23 in the northern hemisphere

Motions of the moonMotions of the moonThe moon rotates on its axisThe moon rotates on its axisThe moon’s rotation takes 27.3 days with The moon’s rotation takes 27.3 days with

the same side always facing the Earththe same side always facing the EarthThe moon seems to shine because it The moon seems to shine because it

reflects sunlightreflects sunlight

Moon Phases – the different forms Moon Phases – the different forms the Moon takes in its appearance the Moon takes in its appearance

from Earthfrom Earth

New Moon – when the moon is New Moon – when the moon is between earth and the sun and between earth and the sun and

cannot be seencannot be seen

Waxing phasesWaxing phases

more of the illuminated half of the moon more of the illuminated half of the moon that can be seen each night after the new that can be seen each night after the new moonmoon

First visible thin slice of the moon is First visible thin slice of the moon is a waxing crescenta waxing crescent

First quarter phase – half the lighted side First quarter phase – half the lighted side of the moon is visibleof the moon is visible

Waxing gibbous – more than one quarter Waxing gibbous – more than one quarter is visibleis visible

All of the Moon’s lighter side is All of the Moon’s lighter side is visible during a full moonvisible during a full moon

Waning phases – less of the Waning phases – less of the illuminated half of the Moon is illuminated half of the Moon is

visible after the full moon.visible after the full moon.

Waning gibbous – starts after a full moon Waning gibbous – starts after a full moon where more than half of the lighted side is where more than half of the lighted side is still visible.still visible.

Only half the Moon’s lighted side is visible Only half the Moon’s lighted side is visible during the third quarter phaseduring the third quarter phase

The last visible slice before a new The last visible slice before a new moon is called the waning crescentmoon is called the waning crescent

Eclipses – when the Earth or the Eclipses – when the Earth or the moon casts a shadow on the othermoon casts a shadow on the other

Solar EclipseSolar Eclipse the moon moves directly the moon moves directly between the Earth and the between the Earth and the Sun, shadowing part of the Sun, shadowing part of the EarthEarth

A total solar eclipse is visible only A total solar eclipse is visible only on a small area of Earthon a small area of Earth

Lunar Eclipse – when Earth’s Lunar Eclipse – when Earth’s shadow falls on the moonshadow falls on the moon

The Moon’s surface has many The Moon’s surface has many depressions, or craters. formed depressions, or craters. formed from meteorites, asteroids, and from meteorites, asteroids, and

cometscomets

Cracks in the Moon’s crust caused Cracks in the Moon’s crust caused lava to fill large craters, forming lava to fill large craters, forming

maria, or dark, flat areasmaria, or dark, flat areas

Data from moonquakes suggest Data from moonquakes suggest that under the Moon’s crust might that under the Moon’s crust might

lie a solid mantle, then a partly lie a solid mantle, then a partly molten mantle and a solid, iron rich, molten mantle and a solid, iron rich,

core.core.

Impact Theory of Moon OriginImpact Theory of Moon Origin

the Moon formed4.6 billion years ago from the Moon formed4.6 billion years ago from Earth material thrown off when a large Earth material thrown off when a large object collided with Earthobject collided with Earth

Impact BasinsImpact Basins or craters, are or craters, are depressions left by depressions left by objects striking the Moon objects striking the Moon (or anything else!!!!!)(or anything else!!!!!)

Quiz conceptsQuiz concepts

AXIS ROTATIONAXIS ROTATIONREVOLUTION ELLIPSEREVOLUTION ELLIPSEMAGNETIC FIELDMAGNETIC FIELDEARTH TILT SEASONSEARTH TILT SEASONSANGLE OF SUNLIGHTANGLE OF SUNLIGHTSOLSTICE EQUINOXSOLSTICE EQUINOXWAXING PHASES WAXING PHASES WANING PHASES MOON PHASESWANING PHASES MOON PHASES