Earth's Motion and Seasons

People once thought the Earth was flat Today we know its shape is a Sphere

Earth’s Location Earth is located in a collection of stars called a Galaxy The kind of galaxy is called a spiral galaxy and Earth is located on one of the arms. The name of the galaxy that Earth is located in is the Milky Way

Solar System The Earth is the 3rd planet of nine planets that revolves around the sun. The Earth’s orbit is the curved path it follows as it travels around the sun.

Earth’s Travels People once believed everything traveled around the Earth. Now we know it is the Earth that moves. It both rotates and revolves.

The Earth’s axis is the imaginary line around which the Earth spins (rotates) causing the Earth to tilt (23.5) toward and away from the sun during different times of the year.

The spinning of the Earth on it’s axis which causes day and night is called Rotation The motion of the Earth around the sun which takes about 365 ¼ days or one year to complete is called a Revolution

Sun’s Path It is Earth’s rotation that gives the apparent motion of the Sun through the sky. Calculating Sun’s height at Summer solstice: (90o-latitude)+23.5o Winter: (90o-latitude)-23.5o

Is the Earth Moving around the Sun or is the Sun moving around the Earth? The Sun’s gravity being so much larger than any planet exerts gravitational force on each planet near it.

Earth’s Revolution Earth revolves around the Sun in an elliptical orbit. The Sun is at one foci of the ellipse. (Time for one revolution = 365 1/4 days = 8,766 hours ) The speed of earth’s revolution is about 18 miles per second.

Earth’s Rotation Earth rotates on an imaginary axis that runs through its pole. Earth’s axis is tilted 23.5o Earth’s rotation gives us our day. Earth makes one complete rotation in 24hrs, 15o every hour. The speed of rotation 24,855 miles/24 hr or 1,038 miles/hr

Proximity to Sun The closer a planet is to the Sun in its orbit the faster it moves. In other words closer planets have a shorter year. Mercury’s year is 88 days, Earth’s is 365.

Gravity of Moon Causes tides The gravitational attraction of the moon causes the oceans to bulge out in the direction of the moon. Another bulge occurs on the opposite side, since the Earth is also being pulled toward the moon (and away from the water on the far side)

The Earth’s Tilt The Earth has 4 seasons. Summer, Spring, Autumn, and Winter. These seasons are caused by Earth’s Tilt

The seasons depend on which side of Earth is tilted toward the sun. When the Northern Hemisphere is tilted toward the sun it is summer in the north and winter in the south and vice versa.

Day vs. Night During the summer the number of hours of daylight is longer and the number of hours of darkness is shorter. During the winter it is just the opposite. Longer nights and shorter days.

Solstices The solstices are the longest and shortest days of the year. The Summer Solstice is the longest and the winter solstice is the shortest.

Northern Hemisphere During the Summer Solstice, the Earth is tilted as far toward the Sun as possible. During the Winter Solstice, the Earth is tilted as far away from the Sun as possible.

Winter Solstice for Northern Hemisphere Summer Solstice for Southern Hemisphere

Summer Solstice for Northern Hemisphere Winter Solstice for Southern Hemisphere

Equinoxes During the Equinoxes the Earth is neither pointing toward or away from the Sun. During the Spring and Fall equinox the length of day versus night is equal.

Moon Phases The phase of the moon you see depends on how much of the sunlit side of the moon faces Earth

Moon Phases Waxing Gibbous Waxing Crescent 1st Quarter New Moon Waning Gibbous Waning Crescent 3rd Quarter Full Moon

Moon Phases The shadow on the moon always disappears from right to left when the moon is growing. If you can see the right side of the moon, then it is growing. The moon always disappear from left to right as well. So if you can see the left side then it is getting smaller.

What phase? 3rd Quarter

When the moon grows it is said to be Waxing When the moon gets smaller it is said to be Waning