Homework 3, Astr305V, Fall 2009, Due date: September 22, 2009.

Greenhouse efffect and its role for sustaining life.

IMPORTANT: cite your references that you found and consulted for any of the answers below.

a. Describe what the greenhouse effect on Earth. Note that I am not asking about how it works in a greenhouse but how it works for the Earth itself.

b. The Earth and the Moon are both about equally distant from the Sun, so they receive the same amount of sunlight per unit area on the surface. It seems reasonable then to attribute most of the differences in temperatures between Earth and Moon to the greenhouse effect of the Earth's atmosphere. Find out the difference between the temperatures on the lunar surface (away from the poles), on the day side (that is the side of the moon that receives sunlight) and the moon's night side (no sun light; note that day and night on the moon are each about 14 earth days long!). Compare this with the same figures for the Earth. By limiting your answer to the equator for the Earth, you remove much of the seasonal variation so we don't have to worry about that.

Now answer the following questions:

b1. Describe the different temperatures you find on the moon and compare them to the temperatures that we know are good for sustaining life on earth. We know that there are several reasons why we can't survive on the moon without a lot of help. Why do astronauts have to wear space suits on the moon? Think of several functions these suits have to provide.

b2. Is the greenhouse on earth a bad thing for life?

b3. What is meant with "global warming" on Earth?

b4. For extra credit: Note that besides raising the overall average temperature, the principal effect of the greenhouse effect is to reduce the difference between day and night time temperatures. Is the greenhouse effect the only factor that causes the difference between Earth's day and night temperatures to be much less than on the Moon, or is/are there other factors? Explain.

Footnote (not needed for your answers above, but something to note):

Note that "global warming" and "ozone depletion ("the ozone hole")" are not the same thing. Make sure you understand the difference between the two.