2. Earth-Sun Relationships The amount of solar energy received by the earth varies with : latitude, time of day, and season. Unequal heating of the earth creates winds and drives ocean currents.

3. Earth’s Motions Rotation: spinning on its axis once every 24 hours. Revolution: moves around the sun in its orbit every year.

4. Seasons Occur because Earth’s position relative to the sun is constantly changing. If the earth were not tilted on its axis at 23.5 degrees, we would not have seasons.

5. The Effects of Earth’s Tilt • At one point, the northern hemisphere of Earth is tilted toward the Sun, while six months later it is tipped away from the Sun. • As a result of the tilt of Earth’s axis and Earth’s motion around the Sun, the Sun is at a higher altitude in the sky during summer than in the winter.

6. The Effects of Earth’s Tilt Altitude is measured in degrees from the observer’s horizon to the object. There are 90 degrees from the horizon to the point directly overhead, called the zenith of the observer.

7. Insolation is a measure of solar radiation energy received on a given surface area and recorded during a given time. The northern hemisphere has more insolation in the summer because the sun shines at a greater angle (closer to 90 degrees)

8. Summer Solstice June 21 or 22 Northern Hemisphere is leaning toward sun First day of summer At the Arctic Circle on this day, daylight is 24 hours because the earth is tilted so the “top” is fully “lit”.

9. Winter Solstice December 21 or 22 First day of winter Earth is tilted AWAY from the sun.

10. Equinoxes Autumnal (vernal) equinox is Sept. 22 or 23 Spring equinox is March 21 or 22 On these days the earth is tilted but NOT toward OR away from the sun. Sun’s rays strike equator vertically.

11. Review What is the general process that causes the seasons? Is the Earth closer to the sun in the Northern Hemisphere's winter or summer? What is the relationship between the Earth and the sun during each of the four seasons in the northern hemisphere?

12. revolution and rotation- include for each season: • date of the year • season in North America • where the sun strikes Earth at a • 90 degree angle • Everyone Copy into your book • A= Timer, B= Artist, C= speaker D= Supplier

13. Bellwork:Thursday, September 5, 2013 • 1. At what angle does earth rotate? • 2. How long does it take for Earth to spin once? • 3. What causes day and night? • 4. What line on Earth’s surface receives vertical light on an equinox? • 5. What hemisphere receives vertical light on our summer solstice?