The Earth in Space
Chapter 2 Sections 2-3
2.2 Movements of the Earth
The movement of the earth around the sun
is called a revolution.
 Each revolution takes 365.24 days, or 1
year.
 The earth also spins on its axis, known as
rotation.
 Each rotation takes 24 hours or 1 day.

2.2 Movements of the Earth
The earth’s orbit is oval shaped.
 At its closest point to the sun, the earth is
at perihelion.
 At its farthest point to the sun, the earth is
at aphelion.
 Perihelion is on January 3rd
 Aphelion is on July 4th

2.2 Movements of the Earth
The earth’s axis is tilted 23.5o from the
perpendicular plane of its orbit.
 During each revolution, the North Pole tilts
at times toward the sun, and at other times
away from it.

2.2 Movements of the Earth
On June 21 or 22, the North Pole tilts
toward the sun.
 The sun’s rays strike the Tropic of Cancer
at 90o.
 This is called the Summer Solstice.
 This is the beginning of summer in the
Northern Hemisphere and winter in the
Southern Hemisphere

2.2 Movements of the Earth
On December 21 or 22, the South Pole
tilts toward the sun.
 The sun’s rays strike the Tropic of
Capricorn at 90o.
 This is called the Winter Solstice.
 This is the beginning of winter in the
Northern Hemisphere and summer in the
Southern Hemisphere

2.2 Movements of the Earth
During the summer solstice all areas north
of the Arctic circle have 24 hours of
daylight and south of the Antarctic circle
have 24 hours of darkness
 During the winter solstice all areas north of
the Arctic circle have 24 hours of darkness
and south of the Antarctic circle have 24
hours of daylight

2.2 Movements of the Earth
On September 22 or 23 of each year, the
sun’s rays strike the equator at 90o.
 This is called the Autumnal equinox.
 This is the beginning of fall in the Northern
Hemisphere and spring in the Southern.
 Equinox means “equal night”. There are
12 hours of daylight and 12 of darkness

2.2 Movements of the Earth
On March 21 or 22 of each year, the sun’s
rays also strike the equator at 90o.
 This is called the Vernal equinox.
 This is the beginning of spring in the
Northern Hemisphere and fall in the
Southern.

2.2 Movements of the Earth
Precession causes the earth’s axis to
wobble, much like a top does as it spins.
 The earth’s axis completes one full circle
every 26,000 years.

2.2 Movements of the Earth
The earth has been divided into 24
standard time zones.
 In each zone, noon is set as the time when
the sun is highest over the center of that
zone.

2.2 Movements of the Earth
The International Date Line is a line
running from North to South through the
Pacific Ocean.
 When it is 8:00 am Friday on the west side
of the line, it is 8:00 am Thursday on the
east side of the line.

2.2 Movements of the Earth
During the summer, most of the United
States uses Daylight Savings Time.
 Clocks move ahead 1 hour in April and fall
back 1 hour in October to provide an extra
hour of daylight in the evening.

2.3 Artificial Satellites
There are hundreds of satellites orbiting
the earth.
 Meteorological satellites gather and
transmit weather information

2.3 Artificial Satellites
Communication satellites relay radio,
telephone, and tv signals around earth
 Navigation satellites send out radio
signals to help ships and aircraft
determine their locations.

2.3 Artificial Satellites
At a height of 36,100 km, a satellite
completes one revolution in 24 hours.
 If a satellite is directly above the equator
and moving in the direction of earth’s orbit,
it is in geosynchronous orbit.
 Communication satellites are put in
geosynchronous orbit.

2.3 Artificial Satellites

The space shuttle is a temporary satellite
that is designed to carry cargo, orbit the
earth, and then return to the earth’s
surface.