Name_______________________________Lab Experiment: Seasons and Angle of Insolation

Have you ever wondered why temperatures are cooler in the winter and warmer in the summer? This happens because the Earth’s axis is tilted. The Earth remains tilted as it revolves around the sun. Because of this tilt, different locations on the Earth receive different amounts of solar radiation at different times of the year. The amount of solar radiation received by the Earth or another planet is called insolation. The angle of insolation is the angle at which the sun’s rays strike a particular location on Earth. When the north end of the Earth’s axis points toward the sun, the Northern Hemisphere experiences summer. At the same time, the south end of the axis points away from the sun and the Southern Hemisphere experiences winter.

In this experiment you will investigate the relationship between angle of insolation and temperature change due to energy absorption from a simulated sun—a light bulb. You will do this for the city of Boston at three times during the year – the summer solstice (Jun 21st ), the winter solstice (Dec 21st) and during an equinox (either Mar 21st or Sept 21st). If time permits, you will also measure temperature changes on those dates for the cities of Nairobi, Kenya, and Melbourne, Australia.

You will not measure the amount of energy in joules or calories. Instead, the temperature will indicate how much of the energy from the light source is available for conversion on planet earth throughout the year. On earth, plants are able to convert that light energy to chemical energy through the process of photosynthesis. The angle of insolation determines how much light energy is available to plants.

Answer the following:

1. At what latitudes are the Tropic of Cancer and the Tropic of Capricorn?

2. If the Earth’s axis were tilted 42º, what would be the latitudes of the Tropic of Cancer and Tropic of Capricorn? What is the significance of the Tropics of Cancer and Capricorn in terms of the noon Sun elevation?

3. At what latitudes are the Arctic Circle and the Antarctic Circle?

4. If the Earth were tilted 42º, at what latitudes would you find the Arctic Circle and the Antarctic Circle?

5. What is the significance of the Arctic Circle and Antarctic Circle in terms of the noon Sun elevation?

6. How many sunrises and sunsets will occur during the year at the North Pole?

Directions: Record the Angle of Insolation for the following cities on the planet. You will do this measuring on a globe, calculating, and by research.

city Latitude Angle of Insolation

Dec 21

(Solstice)

Angle of Insolation

Mar 21

(equinox)

Angle of Insolation

Jun 21

(Solstice)

Angle of Insolation

Sept 21

(equinox)

Boston, Mass.

Melbourne,

Australia

Nairobi, Kenya

Part 1: Measuring Angle of Insolation

It would be possible to calculate the angle of insolation for each location at each date by actually travelling to each location at the correct date. At noon on the designated day, you could measure the angle from the horizon to the sun using a protractor or more accurately a sextant.

Name______________________

Imagin that we were able to do this. In the chart below predict the order (highest angle of insolation being #1 to lowest angle of insolation being #12)

city Angle of Insolation Dec 21

(Solstice)

Angle of Insolation Mar 21

(equinox)

Angle of Insolation Jun 21

(Solstice)

Angle of Insolation Sept

21

(equinox)

Boston, Mass.

Melbourne, Australia

Nairobi, Kenya

Part 2: Calculating the angle of insolation at noonMeasure the number of degrees of latitude separating that location from the latitude that is receiving direct vertical rays (90°). Record as “Relative Latitude”, and be sure to pay attention to N or S.Then subtract that value from 90° to calculate the angle of insolation.

Part 3: Research the angle of insolation: Use the RSI seasons program and click on “CHANGE AXIS TILT” at top of page then “AXIS TILT and SUN ELEVATION”

Or use following link : Use the RSI Seasons program or if you have JAVA you can use http://solarelectricityhandbook.com/solar-angle-calculator.aspx

city Latitude Angle of Insolation

Dec 21

(Solstice)

Angle of Insolation

Mar 21

(equinox)

Angle of Insolation

Jun 21

(Solstice)

Angle of Insolation

Sept 21

(equinox)

Boston, Mass.

Melbourne, Australia

Nairobi, Kenya

Figure 1: Earth in Space and Angle of Insolation