1. The Earth in Space
Chapter 2 Sections 2-3

2. 2.2 Movements of the Earth
The movement of the earth around the sun is called a revolution.
Each revolution takes days, or 1 year.
The earth also spins on its axis, known as rotation.
Each rotation takes 24 hours or 1 day.

3. 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

4. 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.

5. 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

6. 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

7. 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

8. 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

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 2.3 Artificial Satellites
There are hundreds of satellites orbiting the earth.
Meteorological satellites gather and transmit weather information

15. 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.

16. 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.

17. 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.