Exercise 12 – Pg. 173 Earth – Sun Relations

Weather The state of the atmosphere at a particular place for a short period of time. Described by measuring the four basic elements: temperature, moisture, air pressure, and wind (direction and velocity).

Temperature Most important variable; it controls the other variables. Example cool air high pressure system, and warm air low pressure system. Earth is heated from the Sun.

Solar Heat Intensity - the angle at which the rays strike the surface of the Earth. Duration- number of hours of daylight in a 24 hour period. They both will determine the amount of solar radiation any place on Earth will receive.

Ray Diagram on Pg 174 The angle from the Sun to point A is 90O. The sun beam projected will cover an area of 10mm. If the angle from the Sun to point B is 30O. The sun beam projected will cover an area of 17mm. Thus the rays hitting point A are concentrated in a smaller area thus are Stronger

Solar Radiation Why is it warmer at the equator? The greater the angle the stronger the intensity. Tropic of Cancer – 23.5 N Lat. Tropic of Capricorn – 23.5 S Lat.

Solar radiation would be constant if it were not for: The Earth’s rotates on its axis on a 23.50 and revolves around the Sun Throughout the year the Earth’s axis is pointed to the same place. The Earth rotates counter clockwise One whole revolution = 24 hours. If the Earth was not titled then we would not have seasons.

Days of the year Summer Solstice – (ours June 20-22) longest day of the year the day with the greatest number of hours of daylight. Winter Solstice – (ours Dec 21) shortest day of the year because it is the day with the least hours of daylight.

Circle of Illumination This is what gives us darkness at night and light during the day. Arctic circle – 66.5 ON Latitude Antarctic circle – 66.5 OS Latitude Both have 24 hours with and without sun.

Equinox Rays of the Sun are migrating between the Tropic of Cancer and the Tropic of Capricorn. At this time rays of the Sun are vertical at the equator. Equal hours of darkness and light (12 hours) This occurs Mar 21-22 and Sept 22-23

Solstice # 1 June 20-22 For us this is the Summer Solstice. Rays of the Sun are directed toward the Tropic of Cancer. The rays hit this area at 90O. If we lived below the equator then it would be the Winter Solstice. Because of the tilt, more solar intensity hits the tropic of Cancer and less at the tropic of Capricorn. Circle of illumination South pole 0 hrs of sun and North pole 24 hours of sun.

Equinox Suns rays hitting Equator at 90O angle Less at both tropics First day of spring and fall. March 21 - 22 and Sept. 21 - 22 Circle of illumination cuts through the poles, thus 12 hours of light and dark at the poles.

Solstice # 2 Dec. 20-22 For us this is the Winter Solstice. Rays of the are directed toward the Tropic of Capricorn. The rays hit this area at 90O. At this time the rays hit the equator at less then 90O. The rays hit the Tropic of Cancer at a smaller angle. Remember the greater the angle the stronger the intensity. Circle of illumination N pole 0 hrs of sun and South 24 hours of sun.

The Sun is Directly Overhead Tropic of Cancer 23.5O N Lat. Overhead on June 21 Equator 0O Lat. Overhead Mar 21 and Sept. 21 Tropic of Capricorn 23.5O S Lat. Overhead Dec. 21

Analemma Figure 12.6 pg 177 Tells us where the sun is overhead at noon time in the world. Used for navigation before GPS. Nov.4 the sun is overhead at noon time at 15O S Latitude Today April 14 – 9O N Latitude

Chapter Summary pg 181 Questions 4, 5, 6, 7 & 11