Activity 1: Make an Earth
--Complete this activity prior to proceeding to Unit 1--
By physically making a small globe, you will get a better feel for how coordinate systems work. Adding a few important cities will provide a bonus review of geography.
What you will need:
What to Do:
1 - Decide which point on your earth ball is the North Pole (latitude 90 deg N). Mark that in some way.
2 - Mark the point opposite the North Pole. That is the South Pole (latitude 90 deg S).
3 - Midway between the North Pole and the South Pole is the equator (latitude 0 deg). Mark the equator on your earth.
4 - Now, mark the Prime Meridian (longitude 0 deg E or W). It is a line (half circle) from the North Pole through the equator to the South Pole. Label this line PM.
5 - Continue the line that began as the Prime Meridian, and finish drawing it all the way around your earth. The half of this line (circle) on the earth, that is opposite the Prime Meridian, is at longitude 180 deg E or W (the same thing in this case). This approximately marks the location of the International Date Line. Label this line IDL.
6 - Next, draw two more meridians (longitude lines that circle the globe) at 90 deg east and 90 deg west. These lines are halfway between the Prime Meridian and the International Date Line.
Once you have completed Step 6, you now have your world divided into 4 longitudinal sections around the equator, with each section being 90 degrees. Now, divide each of those four sections in half by drawing more longitude lines (meridians).
7 - Looking down on the North Pole of your earth, draw the additional longitude lines and label them as they are in the graphic to the left.
8 - Still looking down on the North Pole, divide each of the eight sections into three subsections. Currently each 1/8th section is 45 degrees. Dividing that into three small sections will mean that each small section is 15 degrees. Label each section to read the correct angle measure (starting with 0, then 15, 30, 45 etc).
So far you have only drawn "great circles." These are circles whose centers lie at the center of the sphere. Now you need to add latitude circles to your globe. These circles will be parallel to the equator. These latitude circles get smaller closer to the North Pole and the South Pole.
- Halfway between the equator and each pole, draw a line around the
earth. If you placed it exactly between the equator and the poles,
the two lines are lines of constant latitude, north and south, and
45 deg latitude.
Get Ready to Mark
Use the coordinates below to mark on your earth the locations of the cities listed. If you are ambitious, you can then color in roughly where the major continents lie using a map or another globe for a guide.
In some upcoming work you will be examining what a person can see from various places on the earth in relation to their local horizon. If you have trouble visualizing what is and what isn't visible to your observer, you may find the following "horizon device" helpful:
Take a stiff piece of cardboard and attach a piece of string or yarn to its center - ideally, by threading it through but taping it on will also work.
Place the cardboard on top of the globe or earth you have made with the yarn stretching away from the globe.
Place the cardboard so that the yarn comes out of the point of contact. This is where we imagine that the observer is standing.
Anything that the yarn can "point to" without
bending is above this observer's horizon.
Bent yarn - like this - leads to points below the horizon. This means that the observer can't see the star or celestial object because it is outside the observer's meridian.