Simple variations in temperature on a globe

What the Activity is for

Here you can show how the top and bottom of a globe are warmed less than the parts facing the source of illumination.

What to Prepare

• A size 1 football or (better but rarer) a 15 centimetre diameter foam globe, marked with north and south poles
• A strip of black paper, about 3 centimetre wide, stuck from north pole to south pole of ball or globe
• A small non-contact thermometer
• A sunny day, or a beam of light more than 30 centimetre across.
• A cocktail stick and blu-tack to act as a shadow stick on the globe
• 3 of 2.5 cm square pieces of thermochromic film stuck to the globe or ball along one line of longitude, approximately at the Equator and 40 degrees north and south

What Happens During this Activity

Place the cocktail stick upright on the Equator, and use it to make sure the beams of light are falling straight onto the globe at this point, and directly onto the strip of black paper. Leave for a minute or two, depending on how sunny the day is. Then use the thermometer to measure the temperature from the north pole to the south pole, sketching the variation. You'll find a maximum at the Equator. Ask why this is (direct illumination, so the the warming effect is shared over less area).

Now model summer in the Northern Hemisphere, by tilting the axis of the globe. Use the shortening of the shadow cast by the cocktail stick, now placed at about 40 degrees north, as extra evidence that this is summer. Again measure the temperatures. Now model winter, looking for a longer shadow.

You can repeat the process using thermochromic film, but trials showed this to be less convincing, as it all tends to change colour rather rapidly.