Unit 1 : Activity 1 : Talking About Things in the Sky : "Which Way is North?" : What's Up? : Unit Exam

# 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:

A spherical object (a rubber ball, a Ping-Pong ball). Some students have used inflatable balls, as they are easier to carry around and are large enough to work with. Don't use anything that will rot -- you will want to use this for quite a while.

A pen capable of marking on the object. You will probably find the globe more useful if you use a pen with ink that will not rub off too easily.

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.

9 - 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 are at 45 deg latitude.

10 - If your sphere is not too small, you can further subdivide each 45 deg latitude section into 3 sections of 15 deg each. Hint: The distance between any two latitude circles at 15 deg apart, is the same as that between any two longitude lines where they cross the equator.

Congratulations, you now have a coordinate globe for the earth with 24 longitude zones. Each corresponds to an hour of time difference (24 zones for 24 hours of rotation). You also have as many as 12 latitude zones.

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.

 Major City Latitude Longitude Barrow 71 N 157 W Buenos Aires 34 S 58 W Cairo 30 N 31 E Calcutta 22.5 N 88 E Capetown 34 S 18 E Chicago 42 N 87.5 W Honolulu 21 N 158 W London 51.5 N 0.0 W Los Angeles 34 N 118 W Mexico City 19.5 N 99.5 W Moscow 56 N 37.5 E New York 41 N 75 W Paris 49 N 2E São Paulo 23.5 S 47 W Shanghai 31 N 121 E Sydney 34 S 151 E Tokyo 36 N 140 E Tromso 68.5N 17 E

Horizon Views

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.