Solar energy and the Earth s seasons

Transcription

1 Solar energy and the Earth s seasons Name: Tilt of the Earth s axis and the seasons We now understand that the tilt of Earth s axis makes it possible for different parts of the Earth to experience different seasons at different times. NH = SH = SUMMER Earth s orbit Equator SPRING South Pole NH = spring SH = autumn SUN North Pole WINTER NH = SH = AUTUMN NH = spring SH = autumn * NH=Northern Hemisphere * SH = Southern Hemisphere The tilt of the axis affects the angle at which the Sun s rays shine on the Earth. This affects the intensity of the Sun s radiation on the Earth. The intensity of the radiation from the Sun is what causes us to experience differences in temperature during the seasons. Look at these diagrams which show how the intensity of radiation is affected by the tilt of the axis.

2 vernal equinox (March 20/21) solstice (June 21/22) Activity: spring autumn autumnal equinox (September 22/23) solstice (December 21/22 autumn spring Angle of Light affects Intensity of Heat Try this experiment to see how the angle at which light shines on a surface affects the heat of that surface. Apparatus: a desk lamp, 2 pieces of black cardboard (10cmx10cm), two strip thermometers, stop watch or timer. 1) Place one piece of black cardboard on a desk and place the strip thermometer on top of it. 2) Position the lamp directly above the thermometer so that the light is shining on the thermometer at a 90 angle. 3) Time this for 30 seconds and then record the temperature. 4) Repeat exercise with the second piece of cardboard and the second strip thermometer. 5) Now position the lamp at an angle to the thermometer. (See diagram.) 6) Time this for 30 seconds and record the temperature.

3 lamp positioned at direct angle lamp positioned at indirect angle strip thermometers placed on black card Answer these questions in your class workbook: 1) What were the temperatures for each of your experiments? a) Direct angle b) Indirect angle 2) At which angle was the heat more intense? 3) Write a conclusion about how the angle of the light affects the intensity of heat on the object. Intensity of solar radiation When light shines directly on an object, the intensity of heat is greater than if it shines on that object at an angle. We know that the Sun radiates light and heat in all directions. When the Sun s light and heat radiates onto the Earth s surface, some rays will shine directly onto the surface and others will shine at an indirect angle. In our South African, the Sun s rays shine directly on the Southern Hemisphere meaning the heat is more intense. The Sun s rays also shine on the Northern Hemisphere, but at an oblique angle, meaning the heat is less intense. Oblique rays Equal amounts of solar energy Direct rays small angle large angle A B small large N 21 December S

4 In our South African, the Sun s rays are shining on the Southern Hemisphere at an oblique angle. This means that the heat is less intense and this is why is cold. In spring and autumn, neither hemisphere is tilted closer to the Sun, so the Sun s direct rays fall on the Equator, and shine on us, in South Africa, at an angle. FUN FACTS S large N small A 21 June B large angle Direct rays Oblique rays Equal amounts of solar energy There are four points in Earth s orbit that mark the middle of each season: In the Southern Hemisphere: 21 December - Summer solstice 21 March - Autumnal (autumn) equinox 21 July - Winter solstice 21 September - Vernal (spring) equinox Length of day and the seasons We know that the Earth rotates and this gives us day and night. The tilt of the Earth s axis determines how long that day and night will be. In we have longer days and shorter nights. In we have shorter days and longer nights.

5 sun rays Consider this diagram: Southern Hemisphere Summer The line that separates day from night is called the circle of illumination. To compare the length of day and night, we will need to look at the lines of latitude (equator and tropics) in relation to this circle of illumination. Earth Axis Summer solstice (21 December) in Southern Hemisphere Arctic Circle Tropic of Cancer Equator Tropic of Capricorn Antarctic Circle 1) Look at the equator. Compare the length of the line during the day and the length of the line during the night, in. What does this mean? 2) Look at the Tropic of Capricorn. Which side of the line is longer? The part representing the day or the part representing the night? What does this mean? 3) What do you notice about the Antarctic Circle? What does this mean regarding their day time and night time during? Consider this picture: Southern Hemisphere Winter Earth Axis Arctic Circle sun rays Tropic of Cancer Equator Tropic of Capricorn Antarctic Circle Winter solstice (21 July) in Southern Hemisphere

6 Answer sheet Activity: Angle of Light affects Intensity of Heat 1) What were the temperatures for each of your experiments? a) Direct angle b) Indirect angle These will differ depending on the thermometers used, however, the direct angle measurement should be higher than the indirect angle measurement. 2) At which angle was the heat more intense? At the direct angle or 90 3) Write a conclusion about how the angle of the light affects the intensity of heat on the object. When light shines on an object at a direct angle the heat is more intense. When light shines on an object at an indirect angle the heat is less intense. Consider this diagram: Southern Hemisphere Summer 1) Look at the equator. Compare the length of the line during the day and the length of the line during the night, in. What does this mean? The length of the line is the same during the day and night. This means that the length of the day is the same as the length of the night. 2) Look at the Tropic of Capricorn. Which side of the line is longer? The part representing the day or the part representing the night? What does this mean? The line during the day is longer than the line during the night. This means that the day is longer in the. 3) What do you notice about the Antarctic Circle? What does this mean regarding their day time and night time during? The line is entirely during the day. This means that it is day time for a full 24 hours! There are no hours of darkness during their. Consider this picture: Southern Hemisphere Winter 1) Look at the equator. Compare the length of the line during the day time and the length of the line during the night time, in. What does this mean?

7 It is the same length in the day and the night. This means that the day is as long as the night. 2) Look at the Tropic of Capricorn. Which side of the line is longer, the part during the day or the part during the night? What does this mean? The line is longer at night than during the day. This means that in, the days are shorter and the nights are longer. 3) What do you notice about the Antarctic Circle? What does this mean regarding their day time and night time during? The line is entirely during the night. This means that it is night for 24 hours in ; there are no hours of daylight during.