Section One: Earth in Space

 What effects are caused by the motions of Earth and the moon?

 1. Demonstrate how Earth moves in space.  Explain what causes the cycle of the seasons.

Astronomy-study of moon, stars, and other space objects I. How Earth Moves in Space -Earth moves through space in two major ways- rotation and revolution A. Rotation 1. axis- imaginary line that passes through Earth’s center and the North and South poles 2. rotation- spinning of Earth on it’s axis a. causes night and day b. rotates East to West c. Takes about 24 hrs. for Earth to rotate once = 1 day

B. Revolution 1. Revolution- movement of 1 obj. around another 2. 1 complete revolution of Earth around sun = 1 yr. 3. Orbit- elongated path Earth moves in around sun C. Calendars 1. Calendar- system of organizing time that defines beginning, length, and divisions of a yr.

days = 1 yr. 3. Earth orbits sun in about 365 ¼ days 4. Every 4 yrs there is an extra day added (leap year) to make up for this. II. The Seasons on Earth A. How Sunlight Hits Earth 1. Sunlight hits Earth most directly near equator *warmer weather 2. Near poles of Earth, sunlight arrives at steep angles, so it is spread out over a greater area

B. Earth’s Tilted Axis 1. Earth has seasons because its axis is tilted as it revolves around the sun 2. It is tilted at an angle of 23.5 degrees 3. As Earth revolves around sun, north end of its axis is tilted away from sun for part of yr.

C. Earth in June 1. North end of Earth’s axis tilted toward sun (summer in northern hemisphere and winter in southern) D. Earth in December 1. Southern hemisphere receives the most direct sunlight (summer in southern hemisphere and winter in northern hemisphere) E. Solstices 1. Happen twice/yr in June and December 2. Solstice- Sun is farthest north or south of equator

3. Farthest north, summer solstice in northern Hemisphere and winter in southern hemisphere 4. Sun farthest south, winter solstice in northern hemisphere and summer solstice in southern hemisphere F. Equinoxes 1. Happen twice a yr in March and September 2. Equinox- “equal night” day and night are ea. about 12 hrs. long

 Explain what effects are caused by the motions of the Earth and moon.  Explain the two ways Earth moves in space.  Explain what causes the cycle of seasons on Earth.