Science 2.1

2.1 Earth rotates on tilted axis and orbits the Sun

Earth’s rotation causes day and night.
Earth’s gravity pulls objects toward the center of Earth. You are turning as Earth turns. You keep the same position with respect to what is below your feet, but the view above your head changes.

*No matter where the person stand, the direction of down will be toward Earth’s center

Earth rotates around axis of rotationThe ends of the axis are the north and south poles.
Earth turns on its axis in 24hours. When a location is in sunlight, it is daytime and night when a location is in darkness. When a location is in the middle of the sunlit side, it is noon and midnight when the location is in the middle of the unlit side.




Earth’s tilted axis and orbit cause seasons
The gravity causes Earth and other objects near the Sun to be pulled toward the Sun’s center. Earth moves sideways, at nearly a right angle to the Sun’s direction.
*It takes a year for Earth to orbit the Sun once.
*In astronomy, a revolution is the motion of one object around another and can also mean the time it takes an object to go around once.

*Earth rotates at about a 23 angle, or tilt, from this lined up position.

*Earth’s orbit is not quite a perfect circle. In January, Earth is closer to the Sun than it is in July. However, the combination of Earth’ motion around the Sun with the tilt of Earth’s axis does cause important changes of temperature.


Angles of Sunlight
The Angles of sunlight change with the seasons. Energy from sunlight is most concentrated when the Sun is high in the sky, resulting in shorter shadows. Because the sunlight is more concentrated, more of the Sun's energy warms the ground. When the Sun is lower in the sky, sunlight is less concentrated, shadows are longer, and less of the Sun's energy warms the ground

Near the equator, the noonday Sun is almost overhead every day, so the ground is warmed strongly year round. In the middle latitudes, the noon Sun is high in the sky only during part of the year. In winter the noon Sun is low and warms the ground less strongly.


Lengths of Days
Lengths of days change with the seasons.

The greatest changes occur near the poles, which experience six months of daylight and then six months of darkness.

The least amount of change occurs at the equator, where periods of daylight and darkness are almost equal all year long.