1.  Reasons for the Seasons Subject: Science Topic: Astronomy

2. ASTRONOMY Astronomy ~ the study of space including:. 1. stars 2. planets 3. other objects AND their origins

3. ROTATION The spinning around a central point or axis. Causes ~ day & night Rotates from West to East 1 Rotation = 1 Day Ex: Earth rotates in 24 hr.

4. REVOLUTION To travel in a circular path around another object. 1 Revolution = 1 year ORBIT ~ the path an object takes as it revolves around something. Earth orbits the sun in 365 ¼ days Earth’s orbit nearly a perfect circle – a slight ellipse

5. EARTH’S TILTED AXIS Tilted at 23.5° angle from the vertical Axis tilted toward the sun in northern hemisphere during summer. a. longer periods of daylight b. physically farthest from sun (about 152 million km)

6. EARTH’S TILTED AXIS Tilted away from sun in northern hemisphere during winter. a. shorter periods of daylight b. physically closest to the sun in winter (about 147 million km)

7. EARTH’S SEASONS

8. The Real Reasons for the Seasons Seasons: Spring, Summer, Autumn & Winter Both Earth’s tilted axis AND its revolution around the sun cause the seasons. Distance from the sun is NOT the reason for the seasons.

9. How Sunlight Strikes the Earth 1. At equator sunlight strikes earth directly. It is usually around 80-88 degrees all year! Difference in temperature from winter to summer is only 1 degree. 2. Closer to the poles sunlight strikes earth at an angle a. near poles sunlight spreads out over larger area

10. EQUINOX Means ~ equal nights a. length of day & night about equal Noon sun is directly overhead at equator Earth’s tilt not toward or away from the sun. Zero tilt. Vernal Equinox ~ spring begins in N. hemisphere Autumnal Equinox ~ fall begins in N. hemisphere

11. SOLSTICE Noon sun is overhead at 23.5° N (June) 23.5° S (December) Summer Solstice – longest day ( ≈ June 21) 1 st day of summer Sun at it’s highest point Winter Solstice – shortest day ( ≈ Dec. 21) 1 st day of winter Sun at it’s lowest point

12. EQUINOX AND SOLSTICE

13. Interesting Facts  Utah has the greatest number of day light hours in the summer.  The sun’s rays strike the earth the farthest north and the farthest south during the summer and winter solstices.  If you watched the night sky for several hours, the stars would appear to be moving around the North Star, however the stars aren’t moving.