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?
Name______________________
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.
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.
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
Boston, Mass.
Melbourne,
Australia
Nairobi, Kenya
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)
Part 2: Calculating the angle of insolation at noon
Measure 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.
city
Boston, Mass.
Melbourne,
Australia
Nairobi,
Kenya
Angle of
Insolation Dec 21
(Solstice)
Angle of
Insolation Mar 21
(equinox)
Angle of
Insolation Jun 21
(Solstice)
Angle of
Insolation Sept
21
(equinox)
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-anglecalculator.aspx
city
Latitude
Angle of
Insolation
Dec 21
(Solstice)
Angle of
Insolation
Mar 21
(equinox)
Angle of
Insolation
Jun 21
(Solstice)
Boston,
Mass.
Melbourne,
Australia
Nairobi,
Kenya
Figure 1: Earth in Space and Angle of Insolation
Angle of
Insolation
Sept 21
(equinox)