Movements of the Earth

Chapter 2.2

Movements of the Earth: Revolution

1)Movements of the Earth: Revolutiona)This is the movement of the earth around

the sun.b)One revolution is equivalent to one trip

around the sun.c)One revolution is equivalent to

approximately 365 days, or one year.d)The earth travels around the sun at

approximately 106,000 km/h.

Movements of the Earth: Rotation

1)Movements of the Earth: Rotationa)This is the spinning of the earth on its axis.b)One rotation is equivalent to one full spin.c)Each full spin of the earth takes approximately 24

hours, or one day.d)This rotation is the cause of daytime and

nighttime. e)Since the earth rotates in a west to east motion, the

sun appears to rise in the east and set in the west.

The Revolving Earth

1)The Revolving Eartha)The path of the earth around the

sun is not a perfect circle. It is elliptical, or oval shaped.

b)This elliptical path around the sun causes the earth to vary its distance from the sun.

The Revolving Earth

i)Perihelion(1)This is when the earth is closest to the

sun, only 147 million kilometers.(2)The earth reaches perihelion on

January 3rd.ii)Aphelion

(1)This is when the earth is furthest from the sun, only 152 million kilometers.

(2)The earth reaches aphelion on July 4th.

The Revolving Earth

a)As the earth revolves around the sun, the direction of its axes does not change. i)The earth’s North Pole always points to the

North Star.ii)Due to this the North Pole tilts sometimes toward

the sun and sometimes away from the sun. (1)When the north pole tilts toward the sun the

northern hemisphere has longer days.(2)When it tilts away from the sun the southern

hemisphere has longer days.

The Revolving Earth

i)This also causes the amount concentration of the sun’s rays to shift between the northern hemisphere and the southern hemisphere.

(1)The sun’s rays hit the earth parallel to each other. However, the curve of the earth changes the angle at which they hit the earth and the concentration of heat.

(2)When the sun’s rays strike the earth directly overhead, at noon, the sun’s rays are most concentrated and produce the most amount of heat for that area.

(3)This is also the cause for earth’s seasons.

The Seasons

1)The Seasonsa)Two variables cause the seasons.

i)The angle at which the sun’s rays strike the earth’s surface.

ii)The amount of daylight in that area of the earth.

The Seasons

Example: When the North Pole is tilted away from the sun, the angle of the sun’s rays on the Northern Hemisphere is lower. This causes fewer hours of daylight. These two variables cause short days and cold winters in the Northern Hemisphere.

Summer Solstices

1)Summer and Winter Solsticesa)The Summer Solstice

i)Occurs on June 21 or 22 each year.ii)The sun’s rays strike the Tropic of Cancer at 90 degrees.

iii)The sun follows its highest path across the sky.

Summer Solstice

i)Marks the beginning of summer in the Northern Hemisphere.

ii)On this day, North of the Arctic Circle, there are 24 hours of sunlight and south of the Antarctic Circle there are 24 hours of darkness.

Winter Solstice

a)The Winter Solsticei)Occurs on December 21 or 22 each year.

ii)The sun’s rays strike the Tropic of Capricorn at 90 degrees.

iii)The sun follows its lowest path across the sky.

Winter Solstice

i)Marks the beginning of winter in the Northern Hemisphere.

ii)On this day, North of the Arctic Circle, there are 24 hours of darkness and south of the Antarctic Circle there are 24 hours of daylight.

Autumnal and Vernal Equinoxes

1)Autumnal and Vernal Equinoxesa)Equinox means equal night.

i)The number of hours of day and night are equal around the world at that time.

ii)This is due to the fact that the North Pole does not point toward nor away from the sun.

The Autumnal Equinox

a)The Autumnal Equinoxi)Occurs on September 22 or 23 of each year.

ii)The sun’s rays strike the equator at 90 degrees.

iii)Marks the beginning of fall in the Northern Hemisphere.

The Vernal Equinox

a)The Vernal Equinoxi)Occurs on March 21 or 22 of each year.ii)The sun’s rays strike the equator at 90

degrees on the opposite side as when they strike during the autumnal equinox.

iii)Marks the beginning of spring in the Northern Hemisphere.

Precession

a)Precessioni)The circular motion of the earth’s axis.

ii)Caused by forces acting on a spinning body.

iii)These forces are the gravitational pull exerted on the earth by the moon, sun, and other planets.

Precession

i)Due to this circular motion, the North Pole will not always point toward the North Star. However, it takes the earth’s axes 26,000 years to complete a full circle. Therefore, this will not affect us for a very long time.

Time Zones

1) Time Zonesa)Uses the sun for a basis of measurement.b)12:00 noon is defined as the time when the sun is

highest in the sky, or directly overhead. c)If people were to set their clocks by their exact

location, then everyone’s clock would be slightly different.

d)To avoid this, we have divided the earth into 24 standard time zones.

i)The time in each zone is one hour earlier than the zone to its East.

International Date Line

a)The International Date Line was created to state when the date changes from one day to the next.

i)This line runs north to south through the Pacific Ocean.

ii)The line was drawn to not split up islands or countries. iii)In the United States most states use daylight savings

time.(1)This allows us to set our clocks one hour ahead in

the spring to provide an additional hour of daylight, and return our clocks to standard time in the fall.