NAME DATE PARTNER(S) COORDINATE SYSTEMS: LOCATING YOURSELF ON A SPHERE Activity 1: Getting Your Bearings 1. Close your eyes and point to the north. Did you point up? Why or why not? Up is the #1 answer. Think about this response when you answer the next question. Imagine that you were hiking along a trail and the trail suddenly divides. You know that you have to go north. How would you know which way to proceed? You know that you cannot go up ; that makes no sense in this case. What you realize is that north is a planar direction (front, back, sideways) in which you can move. You can use a compass to direct you since the needle (dial) of the compass will point to the magnetic north pole of the Earth (which is currently close to the geographic North Pole) 2. Locate a compass and open it if necessary. The direction in which the needle points is north. If the needle is color coded rather than having an N printed on it, ask the instructor which color represents north. Slowly turn the compass until the N on the compass circumference lines up with the needle. What region of the room is due (exactly) north? Where would you end up in the room if you walked to the southeast? Explorations in Earth and Space Science PSC 1210 Prince George s Community College 45
3. Let s think back to the most common answer to the question Where is north? Looking at a globe, locate the northernmost point on the globe. From your position near Washington, D.C, where does north seem to be on the globe? Think about how a person standing on Earth would be oriented. To help you imagine, take a toothpick and break it in half. Take a small piece of clay and place it on Washington, D.C. and place the stick in the clay to represent a person (obviously NOT to scale!) standing upright. Would the person be looking up to the North Pole? Explain. Activity 2: Using Latitude and Longitude Coordinates Suppose you were asked to pinpoint your exact location on Earth. Can you do that with the compass? Explain. If you were in the middle of the ocean with no visible landmarks, would your system work? Explain why or why not. Look at one of the Earth globes in the classroom. Explain what the lines running east-west and north-south might represent. The best way to pinpoint your position is to use a grid system. Because planetary bodies like the Earth and Moon are spherical, we need to employ a grid system on a curved surface. As you may recall, the system currently in use defines the North and South Poles as reference points. These points represent the imaginary positions where the rotation axis of the Earth emerges. The current system employs grid lines that measure longitude and latitude. Latitude The equator is an east-west line that encircles the globe exactly midway between the north and south poles. It is designated as 0 o (zero degrees). Additional lines, parallel to the equator and called parallels, are marked off to the north and south. These lines mark the angular distance 46 Explorations in Earth and Space Science PSC 1210 Prince George s Community College
from the equator, a measurement called latitude. Northern latitudes values are marked N or with a plus (+) sign. Southern latitudes are marked with an S or minus (-) sign. The North Pole is designated as 90 o N or +90 o while the South Pole is 90 o S or -90 o. See the illustration below for parallels or lines of longitude. Your latitude is how many degrees north or south you are from the equator. Longitude The series of north-south lines which converge at either pole are called meridians or lines of longitude. They divide the 360 o globe into eastwest sections. You can see these on the diagram here. On any planetary body, a prime meridian with a value of 0 o must be defined so that values can be assigned to the other lines of longitude. On Earth, the prime meridian passes through Greenwich, England. Earth longitude is measured from 0 to 180 o to the west and 0 to 180 o to the east. Your longitude is the number of degrees your site is east or west of the prime meridian. You should note that values from 0 to 180 o W are also sometimes designated as negative values (-85 o equals 85 o W). On other planets, such as Mars, longitude values run from 0 o to 360 o and no east-west direction is implied So, using latitude and longitude, you can locate a position on any planet or moon. In this activity you will explore site location on Earth, the Moon, and Mars. 1. Using the map of the Earth at the end of this activity or an Earth globe, determine the longitude and latitude of the following sites. An atlas is available from the instructor if needed. Point Location Latitude Longitude A B C D Big island of Hawaii Central Iceland Northernmost tip of New Zealand Chesapeake Bay Explorations in Earth and Space Science PSC 1210 Prince George s Community College 47
2. There are approximately 140 known impact structures on the Earth made by space debris. Plot and label the following crater locations on the Earth map printed at the end of this activity. Point Crater Latitude Longitude E Meteor Crater, AZ, USA 35 o N 111 o W F Sudbury, Canada 47 o N 81 o W G Ust-Kara, Russia 69 o N 65 o E H Teague, Australia 26 o S 121 o E I Monturaqui, Chile 24 o S 68 o W 3. Listed in the table below are actual landing sites for the Viking I and II (1976), the Pathfinder (1997) Mars missions, and the Rover Mars missions (2004). Site # Landing Site Latitude Earth System Longitude Mars System Longitude 1 Viking 1 22 o N 50 o W 50 o 2 Viking 2 48 o N 134 o E 226 o 3 Pathfinder 19 o N 34 o W 34 o 4 Spirit 15 o S 176 o E 184 o 5 Opportunity 2 o S 6 o W 6 o Description a. Locate and describe these sites on the Mars map that is available. DO NOT MAKE ANY MARKS ON THE MAP! Explain why you think these sites might have been selected. b. Plot and label the same sites (same longitude and latitude) on the Earth map. Would the Mars landers have been in trouble with any of these sites on Earth? Explain. 48 Explorations in Earth and Space Science PSC 1210 Prince George s Community College
4. Using the National Geographic Society Earth s Moon Map provided, answer the following questions. DO NOT MAKE ANY MARKS ON THE MAP! a. Determine the latitude and longitude for the features listed in the table below: (Use the indices on the front and back of the map for general area location.) Feature Latitude Longitude Copernicus (a crater) Mendeleev (a crater) Apollo 17 landing site Surveyor 7 landing site b. List two features that the lunar prime meridian crosses: c. From lunar latitude and/or longitude values, explain how you could quickly recognize that a feature is located on the far side of the Moon. Explorations in Earth and Space Science PSC 1210 Prince George s Community College 49
50 Explorations in Earth and Space Science PSC 1210 Prince George s Community College
Activity 3: Locating Your Place on Earth Using GPS So, now we know that we can pinpoint our Earth location by using longitude and latitude coordinates. But, how do we know what these coordinates are for the location we are in now? In the past, people have used the position of the stars and exact timekeeping devices. Today we have a more sophisticated system that uses satellites. The Global Positioning System (GPS) involves a series of satellites that beam signals to Earth. A GPS receiver can detect these signals. If the receiver can pick up signals from four satellites, it can use the information to triangulate and determine your exact longitude and latitude and velocity (if you are moving). The more signals received, the more accurate the positioning. You can use this system on land or sea, and most planes and boats are equipped with receivers for navigation. Today, some cars have built in GPS navigation systems. GPS is funded by and controlled by the U. S. Department of Defense (DOD). While there are many thousands of non-government users of GPS world wide, the system was designed for and is operated by the U. S. military. 1. Locate a GPS receiver (Magellan or Garmin) and take it outside the building. Turn the receiver on. You will need to wait for a few minutes as the receiver locates satellite signals. If the receiver is blocked by the buildings, move away into an open area (like a courtyard or parking lot) until the receiver has registered enough satellites to give a position. Record your longitude and latitude here: longitude latitude 2. While watching the receiver, walk some distance from your starting point. Does your position change much? Why or why not? 3. If you are using the Garmin receiver, notice the compass on the top of the display as you are walking. Change direction and walk a distance in the new direction. What happens to the display? Why do you think there is a delay in the receiver response? Explorations in Earth and Space Science PSC 1210 Prince George s Community College 51
52 Explorations in Earth and Space Science PSC 1210 Prince George s Community College