Measuring Time and The Seasons

Objectives Summarize how Earth’s rotation and revolution provide a basis for measuring time. Explain how the tilt of Earth’s axis and Earth’s movement cause seasons.

Measuring Time Earth’s motion provides the basis for measuring time. A day is determined by Earth’s rotation on its axis. Each complete rotation of Earth on its axis takes 24 hours. A year is determined by Earth’s revolution around the sun. Each complete revolution of Earth around the sun takes 365 1/4 days, or one year.

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

Time Zones Earth’s surface is divided into 24 time zones. Each is one hour earlier than the time in the zone to the east. International Date Line: imaginary line which runs from the north to the south pole and separates one calendar day from the next. passes through the middle of the Pacific Ocean, at 180° longitude but deviates to pass around island groups

U.S. Time Zones

Daylight Savings Time Because of the tilt of Earth’s axis, daylight is shorter during winter than summer. The US uses daylight savings time to make better use of daylight: Daylight savings time: clocks are set one hour ahead in April, and are set back one hour in October “Spring Ahead”, “Fall Behind”

The Seasons Seasons are the result of the tilt of the Earth's axis, which is tilted at 23.5°. The number of daylight hours is greater for the hemisphere, or half of Earth, which is tilted toward the Sun. Seasons are not caused by how close the Earth is to the sun! In fact, Earth is closest to the sun on Jan. 3 and farthest on July 4. We call these?

Why We Have Seasons Summer is warmer than winter because the Sun's rays hit the Earth at a more direct angle

More About Seasons Days are much longer than nights during summer and shorter than nights in the winter, due to the tilt of Earth's axis. When the North Pole tilts away from the sun, the angle of the sun’s rays falling on the Northern Hemisphere is low, and we experience fewer daylight hours, less energy, and lower temperatures.

Equinoxes Equinox: equal day and night…12 hours of each At the equinox, the sun’s rays strike Earth at a 90° angle to the equator. The autumnal equinox occurs on September 22 or 23 and marks the beginning of fall in the Northern Hemisphere. The vernal equinox occurs on March 21 or 22 and marks the beginning of spring in the Northern Hemisphere.

Solstices Solstice: point at which the sun is as far north or south of the equator as possible Summer Solstice: longest day of the year, which occurs on June 21 or 22 and marks the beginning of summer in the Northern Hemisphere. Winter solstice: shortest day of the year, which occurs on December 21 or 22 and marks the beginning of winter in the Northern Hemisphere.

Review Look closely at where the Sun is hitting the Earth during each season: http://Search.Lycos.com/setup.asp?r=5&src=clear2&query=weather+savvy

Round One 1. The Earth spinning on its axis. 2. Going around the Sun. Rotation Revolution 2. Going around the Sun. Rotation Revolution Revolution 3. Day composed of 24 hours. Round One Rotation Revolution 4. Causes the Earth’s seasons. Distance from Sun Tilt 5. A year. Rotation Revolution 6. The moon going around Earth. Rotation Revolution

Identify the motion being shown in each of these pictures Identify the motion being shown in each of these pictures. Each team must write their answers for each figure in the form of a question. Figure #1 Rotation Revolution Planet Round Two Figure #2 Earth Rotation Revolution