ACTIVITY 3: TEMPERATURES AND ATMOSPHERES

Concepts:

• temperature scales (convert K to C?)

• graphing

• pie charts

• the effect of an atmosphere

• what surface pressure means

• Using the attached table, graph the average surface temperature vs. orbital distance.

  If desired, convert to C from K, or explain about absolute zero. If using C, this introduces negative numbers.

Q: What trends can you observe from your graph?

A: Students should observe a general trend of decreasing temperature with increasing distance from the sun.

Q: Why do you think this is the case?

A: When planets are farther from sun, they receive less light and therefore less heat and energy to keep the planet warm.

Compare the surface pressure on Mercury, Venus, the Earth, and Mars. The surface pressure is also called the atmospheric pressure -- it's how hard the atmosphere pushes down on us. We don't notice on Earth that there's a thick atmosphere above us pushing down because we're used to it, but if we went to Venus, where the pressure is almost 100 times as high as on Earth, we'd notice that! (we wouldn't be able to breathe -> no oxygen, but also the pressure is too high) One of the effects that Venus' thick atmosphere has is that it traps the heat inside, and doesn't let much of it escape.

• Using the attached table, make pie charts for the compositions of the atmospheres of Mercury, Venus, Earth, Mars

Interpretation:

Q: Which two planets have similar atmospheric compositions?

A: Venus, Mars

Q: What makes these two atmospheres very different?

A: Venus' atmosphere is much, much thicker, so Venus has a much higher surface pressure.

Extra: relate the discussion above of carbon dioxide in Venus' atmosphere to current environmental concerns about "greenhouse gases" in Earth's atmosphere, and the apparent trend of global warming.

Having an atmosphere not only helps keep heat, it also smoothes out the temperature differences between day, when the sun is shining directly down and providing heat, and night, when there's no solar heating at all. On the Earth on a typical day, the temperature variation between day and night is at most 40 or 50 degrees F, since the atmosphere helps save some of the daytime heat to keep us warmer at night. On Mars, which has a very thin atmosphere, the temperatures are not only very cold on average, because there's not much atmosphere to trap heat, but they are also highly variable: the temperature can range from -220 degrees F on a cold winter night to a maximum of 70 degrees F at the equator on a hot summer day. Imagine trying to dress for temperature differences like those!

Bonus activities:

• Gather information on the range of temperatures present on Earth, such as winter in Alaska, a summer day in Tucson, boiling point of water, melting of lead, etc.

• Compare these temperatures to the temperatures on the planets. Would you want to go on vacation to either Venus or Mars?

  no -> Venus is too hot, pressure is too high; Mars is too cold, pressure is too low. Earth is just right!