Chapter 23: Earth-Sun-Moon System Section 1 Earth Notes

1. Chapter 23The Sun-Earth-Moon System Company Name

2. Chapter 23: Section 1: Earth A. Properties of Earth—people used to think that Earth was flat and at the center of the universe. 1. Earth is now known to be a round, three-dimensional sphere. a. Axis—imaginary vertical line around which Earth spins b. Rotation—the spinning of Earth around its axis that causes day and night 2. Earth has a magnetic field with north and south poles. 3. Magnetic axis—imaginary line joining Earth’s magnetic poles a. Earth’s magnetic axis does not align with its rotational axis. b. The location of magnetic poles slowly changes over time.

3. Chapter 23: Section 1: Earth Magnetic Axis: A compass points to magnetic North (not North Pole) The difference between polar North and magnetic north is 11.5 degrees. Earth’s characteristics Only known planet to have liquid water. Made up of 70% water. 97% of water on Earth is salted. Only known planet to have life.

4. Chapter 23: Section 1: Earth Sailors used line of sight to show the Earth was curved Aristotle reasoned that the Earth was round because it cast a round shadow (Not flat) on the Moon during eclipses

5. Chapter 23: Section 1: Earth EARTH INFORMATION (DO NOT COPY IN YOUR NOTES) Diameter: (Pole to Pole) = 7,901 mi. Diameter: (at Equator) = 7,926 mi Earth rotates at about 1000 mi/hr. Mass: 5.98 x 1027 g = 5.98 x 1023 kg Density: 5.52 g/cm3 Average distance from the Sun = 149,600,000 km Period of Rotation (1 day) = 23hr. 56 min. Pd. of Revolution (1 year) = 365 days 6 hr. 9 min. Polar tilt: 23.50 from vertical Average Temperature is 60oF Hottest Temperature: 134oF in Death Valley California (1913) Coldest Temperature: -129oF in Vostok, Antartica (1983) This means the earth is constantly moving around the sun.

6. Chapter 23: Section 1: Earth Causes of Seasons Revolution: Earth’s yearly orbit around the Sun. Earth’s orbit is an ellipse, or elongated, closed curve. Because the Sun is not centered in the ellipse, the distance between the Earth and the Sun changes during the year. Earth’s tilt causes seasons. The hemisphere tilted toward the Sun receives more daylight hours than the hemisphere tilted away from the Sun. The longer period of sunlight is one reason summer is warmer than winter.

7. Chapter 23: Section 1: Earth Causes of Seasons Earth’s tilt causes the Sun’s radiation to strike the hemisphere at different angles. Due to Earth’s tilt on it’s axis (23.5 degrees) The hemisphere tilted toward the Sun receives more total solar radiation than the hemisphere tilted away from the Sun. (more solar energy = warmer temperatures) In the hemisphere tilted toward the Sun, the Sun appears high in the sky and the radiation strikes Earth more directly. Seasons are opposite between hemispheres

8. Chapter 23: Section 1: Earth Causes of Seasons

9. Chapter 23: Section 1: Earth Causes of Seasons Distance from the sun changes during the year Closest to the sun = Perihelion Jan 3rd and is about 91,500,000 miles from the sun. Farthest from the sun = Aphelion July 4th and is about 94,500,000 miles from the sun.

10. Chapter 23: Section 1: Earth Solstice: (means longest) The day when the Sun reaches its greatest distance north or south of the equator. Summer solstice occurs June 21 or June 22 in the northern hemisphere. (Sun reaches the Tropic of Cancer) This is the longest day of the year. (In terms of sunlight) About 16 hours of sunlight that day North pole receives 24 hours of sunlight that day!! South Pole receives 24 hours of night. Winter solstice occurs December 21 or 22 in the northern hemisphere. (Sun directly on the Tropic of Capricorn) (This is the shortest day of the year. (In terms of sunlight) About 16 hours of night North pole has 24 hours of night on that date.

11. Chapter 23: Section 1: Earth Winter Solstice: Summer Solstice:

12. Chapter 23: Section 1: Earth Equinox The day when the sun is directly over Earth’s equator. Daylight and nighttime hours are equal all over the world. Daylight = 12 hours, Night = 12 hours Spring equinox occurs on March 20 or 21 in the northern hemisphere. (Beginning of Spring) Fall equinox occurs on September 22 or 23 in the northern hemisphere. (Beginning of Fall) Spring and Fall dates are reversed for the Southern Hemisphere.

13. Chapter 23: Section 1: Earth Equinox Two equinoxes occur each year. Fall Equinox Spring Equinox