Unit 6 Earth’s Revolution, Rotation, and Seasons Mr. White Earth Science

Earth’s Seasons od_window.html?pid=9

Earth’s Rotation  Rotation is the spinning of the Earth on its axis.  The time for one rotation is 24 hours.  The speed of rotation 24,855 miles/24 hr or 1,038 miles/hr

Earth’s Rotation What does Rotation mean? Rotation occurs when something is spinning around an axis. What are some examples of things that rotate? Tops, Ballerinas, Figure skaters, cyclones, Tornadoes, a merry-go- round, Earth How do we know that the Earth rotates? 1.Star trails- trails made with time exposure, circular paths that occur because the planet is moving and not stationary. 2.Winds curve because of the Earth’s rotation – Coriolis Effect 3.Ocean currents curve clockwise in the northern hemisphere, and counterclockwise in the southern hemisphere. 4.The movement of a pendulum. It does not actually move, it is the Earth moving that causes the pendulum to appear to change the direction of its swing.

Night and Day What causes night and day? The rotation of the Earth  The side of the Earth that is facing the sun has daylight, the side of the Earth away from the sun has night.  It takes 24 hours for the Earth to complete one rotation.  The Earth is tilted on it’s axis at a 23.5 degree angle.  The Earth’s tilt is always in the direction of the North Star. What is another name for the North Star? Polaris  This tilt is what causes our days to get longer in the summer and shorter in the winter.  Because of the Earth’s rotation the sun appears to rise in the east and set in the west.

Earth’s Revolution  A revolution occurs as the earth moves around the sun.  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 Revolution

Earth’s Orbit  Orbit is the path an object takes as it revolves around another object.

Around and Around We Go Every second, that you sit in this classroom, the Earth's orbital motion carries you about 18 miles through space.

Why do we have seasons? The Earth’s orbit around the sun is NOT a perfect circle. It is an ellipse.The Earth’s orbit around the sun is NOT a perfect circle. It is an ellipse. Seasons are not caused by how close the Earth is to the sun.Seasons are not caused by how close the Earth is to the sun. In fact, the Earth is closest to the sun around January 3 and farthest away from the sun around July 4.In fact, the Earth is closest to the sun around January 3 and farthest away from the sun around July 4. The Earth’s orbit around the sun is NOT a perfect circle. It is an ellipse.The Earth’s orbit around the sun is NOT a perfect circle. It is an ellipse. Seasons are not caused by how close the Earth is to the sun.Seasons are not caused by how close the Earth is to the sun. In fact, the Earth is closest to the sun around January 3 and farthest away from the sun around July 4.In fact, the Earth is closest to the sun around January 3 and farthest away from the sun around July 4. Ellipse

Why do we have seasons? Seasons are the result of the tilt of the Earth's axis. Earth’s axis is tilted 23.5°. This tilting is why we have SEASONS like fall, winter, spring, summer. The number of daylight hours is greater for the hemisphere, or half of Earth, that is tilted toward the Sun. Seasons are the result of the tilt of the Earth's axis. Earth’s axis is tilted 23.5°. This tilting is why we have SEASONS like fall, winter, spring, summer. The number of daylight hours is greater for the hemisphere, or half of Earth, that is tilted toward the Sun.

Why do we have seasons? Summer is warmer than winter (in each hemisphere) because the Sun's rays hit the Earth at a more direct angle during summer than during winterSummer is warmer than winter (in each hemisphere) because the Sun's rays hit the Earth at a more direct angle during summer than during winter

Why do we have seasons? Also the days are much longer than the nights during the summer.Also the days are much longer than the nights during the summer. During the winter, the Sun's rays hit the Earth at an extreme angle, and the days are very short. These effects are due to the tilt of the Earth's axis. During the winter, the Sun's rays hit the Earth at an extreme angle, and the days are very short. These effects are due to the tilt of the Earth's axis. Also the days are much longer than the nights during the summer.Also the days are much longer than the nights during the summer. During the winter, the Sun's rays hit the Earth at an extreme angle, and the days are very short. These effects are due to the tilt of the Earth's axis. During the winter, the Sun's rays hit the Earth at an extreme angle, and the days are very short. These effects are due to the tilt of the Earth's axis.

Seasons…in a nut shell

SolsticesSolstices Solstices occur twice a year, when the tilt of the Earth's axis is oriented directly towards or away from the Sun, causing the Sun to appear to reach its northernmost and southernmost extremes.Solstices occur twice a year, when the tilt of the Earth's axis is oriented directly towards or away from the Sun, causing the Sun to appear to reach its northernmost and southernmost extremes. Winter solstice is the shortest day of the year. In the Northern Hemisphere. It occurs on December 21 and marks the beginning of winter.Winter solstice is the shortest day of the year. In the Northern Hemisphere. It occurs on December 21 and marks the beginning of winter. The Summer Solstice is the longest day of the year. It occurs on June 21 and marks the beginning of summer.The Summer Solstice is the longest day of the year. It occurs on June 21 and marks the beginning of summer. Solstices occur twice a year, when the tilt of the Earth's axis is oriented directly towards or away from the Sun, causing the Sun to appear to reach its northernmost and southernmost extremes.Solstices occur twice a year, when the tilt of the Earth's axis is oriented directly towards or away from the Sun, causing the Sun to appear to reach its northernmost and southernmost extremes. Winter solstice is the shortest day of the year. In the Northern Hemisphere. It occurs on December 21 and marks the beginning of winter.Winter solstice is the shortest day of the year. In the Northern Hemisphere. It occurs on December 21 and marks the beginning of winter. The Summer Solstice is the longest day of the year. It occurs on June 21 and marks the beginning of summer.The Summer Solstice is the longest day of the year. It occurs on June 21 and marks the beginning of summer. Tyrrhenian Sea and Solstice Sky Credit & Copyright: Danilo PivatoCopyrightDanilo Pivato

SOLSTICE During the winter the Northern Hemisphere day lasts fewer than 12 hours and the Southern Hemisphere day lasts more than 12 hours.During the winter the Northern Hemisphere day lasts fewer than 12 hours and the Southern Hemisphere day lasts more than 12 hours. During the winter solstice, the North Pole has a 24-hour night and the South Pole has a 24-hour day.During the winter solstice, the North Pole has a 24-hour night and the South Pole has a 24-hour day. Sunlight strikes the earth most directly at the Tropic of Capricorn.Sunlight strikes the earth most directly at the Tropic of Capricorn. During the winter the Northern Hemisphere day lasts fewer than 12 hours and the Southern Hemisphere day lasts more than 12 hours.During the winter the Northern Hemisphere day lasts fewer than 12 hours and the Southern Hemisphere day lasts more than 12 hours. During the winter solstice, the North Pole has a 24-hour night and the South Pole has a 24-hour day.During the winter solstice, the North Pole has a 24-hour night and the South Pole has a 24-hour day. Sunlight strikes the earth most directly at the Tropic of Capricorn.Sunlight strikes the earth most directly at the Tropic of Capricorn. erence/solstice.gif

Equinoxes A day lasts 12 hours and a night lasts 12 hours at all latitudes.A day lasts 12 hours and a night lasts 12 hours at all latitudes. Equinox literally means "equal night".Equinox literally means "equal night". Sunlight strikes the earth most directly at the equator.Sunlight strikes the earth most directly at the equator. This occurs twice a year.This occurs twice a year. A day lasts 12 hours and a night lasts 12 hours at all latitudes.A day lasts 12 hours and a night lasts 12 hours at all latitudes. Equinox literally means "equal night".Equinox literally means "equal night". Sunlight strikes the earth most directly at the equator.Sunlight strikes the earth most directly at the equator. This occurs twice a year.This occurs twice a year. quinox.gif

Equinox The vernal (spring) equinox occurs March 21.The vernal (spring) equinox occurs March 21. The autumnal (fall) equinox occurs September 21.The autumnal (fall) equinox occurs September 21. The vernal (spring) equinox occurs March 21.The vernal (spring) equinox occurs March 21. The autumnal (fall) equinox occurs September 21.The autumnal (fall) equinox occurs September 21.

The Earth's seasons are not caused by the differences in the distance from the Sun throughout the year.

The seasons are the result of the tilt of the Earth's axis. I know this is a repeat, but it is important that you understand this idea. Many Americans, including Harvard graduates, do not know what causes seasons!

Review Look closely at where the Sun is hitting the Earth during each season: