Geography 110H
First Assignment for Fall 199
Due Sept. 10, 1998
This exercise focuses on two things: first, a basic introduction to the earth and its place in the solar system. Second, an introduction to earth/sun relations, the importance of seasonal changes in the way the sun's radiation strikes the earth's surface, and the annual cycle of day length as a function of latitude. The WWW sites listed below will provide information that helps to illuminate these concepts.
1. Look up a site providing general introductory information about the earth and its neighbors. Compare and contrast the earth with its nearest neighbor, Venus, and with its slightly more distant neighbor, Mars. Were you surprised by what you read, or was this information already familiar to you? If you're ambitious, you might consider the following question: what conditions make a planet habitable? Come to class prepared to make a brief oral presentation on your major observations.
Both of the following sites are also in the bookmark list accessible from the class homepage:
"The Nine Planets" (http://www.seds.org/billa/tnp/ )
or another one known as
"Views of the solar system" (http://bang.lanl.gov/solarsys/).
You may,of course, consult other sources as well by doing a search of the
web. For example, here's another site (but it will work only on a
Macintosh): Comparing
Earth and its Planetary Neighbors.
As an alternative, try answering the question "where did the earth's
oceans come from?" (the water, not the ocean basins!) The most recently
advanced hypothesis suggests that small comets are responsible, but there
is a considerable amount of disagreement. What are the competing hypotheses?
What is the evidence on either side of this question and how would you
make up your mind which answer is most likely?
2. Earth-sun relations that govern the duration of daylight and the location of the circle of illumination can be illustrated using the Earth Viewer at the following location:
http://www.fourmilab.ch/earthview/expert.html
You can see the areas in sunlight and darkeness for the particular moment at which you are visiting the site, and you can choose to look at a flat map or a global view centered over any location of your choosing. (The images load slowly, so you may not want to do this at prime time.) If you look at a flat topographic map, note the shape of the line dividing day from night. Now look at it on a global view (click on "above location" and select a latitude, longitude, and altitude above earth's surface before clicking on "View Earth"). What does this say to you about the information provided on maps and the interpretation of coordinate systems?
Try several different views from different latitudes (including polar and equatorial views) and compare what you see with the discussion in the textbook of earth-sun relations for different seasons.
3. The U.S. Naval Observatory maintains a web site called the Directorate of Time. Here is its address:
http://tycho.usno.navy.mil/srss.html
A subset of this web site will allow you to calculate times of sunrise and sunset for one day any location expressed in geographic coordinates:
http://aa.usno.navy.mil/AA/data/docs/RS_OneDay.html
or, alternatively, at the following site, if you type in the name of a U.S. town or city, you can get a whole year's worth of sunrise and sunset times:
http://aa.usno.navy.mil/AA/data/docs/RS_OneYear.html
Visit one of these sites and find times of sunrise and sunset as well as length of daylight for the 22nd day of each month through the year, for each of several latitudes. Tabulate this information and make a plot showing how either time of sunrise and sunset or duration of daylight varies by month; superimpose plots for several different latitudes on the same page. You can also pick a single date and plot how duration of daylight varies with latitude. I will accept any combination of graphs that shows you have explored the range of variation by date and location; provide a brief discussion that relates your observations to the discussion of earth-sun relations in the textbook.
Here's another page with information about the time of "apparent" sunrise and sunset and why it differs from the time of "real" sunrise and sunset: