1. Earth is constantly moving in two ways.
A Earth rotates around its axis once a day.
B Earth revolves around the sun once a year.
Tilt of 23.5°
Axis of rotation
Direction of rotation
Axis passes through poles
Earth’s orbit
Sun

2. What are two ways in which Earth moves?
Earth moves in two major ways: rotation and revolution.

3. Earth spins like a top around an imaginary line, or axis, that connects the north and south geographic poles.
The spinning of Earth on its axis is called rotation.
Earth’s rotation causes day and night as the sun appears to move from east to west across the sky.
It takes one day for Earth to complete one rotation.

4. As Earth rotates on its axis, it also travels around the sun.
Revolution is the movement of one body in space around another.
It takes Earth one year, about 365¼ days, to make a complete revolution around the sun.

5. Earth’s Latitude Zones
How is Earth’s surface divided into zones based on latitude?
Latitude measures distance in degrees north or south of the equator.
Scientists use lines of latitude to mark out three different types of regions within which temperatures are generally similar: the tropic, temperate, and polar zones.

6. Earth’s Latitude Zones
Different parts of Earth receive different amounts of sunlight, depending on their latitude.
Regions near the equator receive more direct sunlight than the poles, so Earth is generally warmer near the equator and colder toward the poles.

7. Earth’s Latitude Zones
Polar zone
The angle at which sunlight strikes Earth’s surface varies with latitude. As a result, it is generally warmer near the equator than near the poles.
Polar zone

8. Earth’s Latitude Zones
Between the latitudes of 23.5° south and 23.5° north is the tropic zone, where Earth is generally warm.
From 23.5° north to 66.5° north and from 23.5° south to 66.5° south are the temperate zones, which are generally cooler than the tropics.
From 66.5° north to the North Pole and from 66.5° south to the South Pole are the polar zones, which are generally cold.

9. The Seasons
What causes the seasons?
The seasons are caused by the tilt of Earth’s axis as it moves around the sun.

10. Earth’s axis of rotation is not straight up and down.
The Seasons
Earth’s axis of rotation is not straight up and down.
The axis tilts at an angle of about 23.5° relative to a line perpendicular to its orbital path.
As Earth orbits the sun, the north end of Earth’s axis points in the same direction, but the orientation of Earth’s axis changes relative to the sun over the course of a year.

11. The Seasons
Solstices
Because Earth’s axis is tilted, the latitude at which the noon sun appears directly overhead changes in a yearly cycle.
A solstice occurs on the two days each year when the sun is directly overhead at latitude 23.5° north or 23.5° south.

12. The Seasons
In the Northern Hemisphere, the summer solstice marks the beginning of summer, around June 21.
The Northern Hemisphere is tilted toward the sun, so it receives more sunlight than the Southern Hemisphere.
On this day, daylight hours are longest in the Northern Hemisphere and shortest in the Southern Hemisphere.

13. The Seasons
Six months later, about December 21, the winter solstice marks the beginning of winter in the Northern Hemisphere.
The Northern Hemisphere is tilted away from the sun. so the Northern Hemisphere receives less sunlight than the Southern Hemisphere.
Daylight hours are shortest in the Northern Hemisphere but longest in the Southern Hemisphere.

14. The Seasons
Equinoxes
Halfway between the solstices are two days, called equinoxes, which mark the beginning of spring and autumn.
At an equinox, neither hemisphere is tilted toward the sun, and the lengths of daylight and of darkness are approximately equal.

15. The Seasons
The vernal equinox, about March 21 in the Northern Hemisphere, marks the start of spring.
The autumnal equinox, about September 22 in the Northern Hemisphere, marks the start of autumn.
On the equinoxes, the noon sun is directly overhead at the equator.
Sunlight reaches the Northern and Southern Hemispheres in equal amounts.

16. The Seasons
The seasons are caused by the tilt of Earth’s axis as it revolves around the sun.

17. What causes the seasons?
Assessment Questions
What causes the seasons?
Earth’s orbit about the sun
Earth’s rotation about its axis
the atmosphere
the tilt of Earth’s axis as it moves around the sun

18. What causes the seasons?
Assessment Questions
What causes the seasons?
Earth’s orbit about the sun
Earth’s rotation about its axis
the atmosphere
the tilt of Earth’s axis as it moves around the sun ANS: D

19. Which of the Earth’s latitude zones receives the most direct sunlight?
Assessment Questions
Which of the Earth’s latitude zones receives the most direct sunlight?
the tropic zone
the temperate zone
the polar zone
They all receive the same amount of direct sunlight.

20. Which of the Earth’s latitude zones receives the most direct sunlight?
Assessment Questions
Which of the Earth’s latitude zones receives the most direct sunlight?
the tropic zone
the temperate zone
the polar zone
They all receive the same amount of direct sunlight. ANS: A