Where in the World…. THE GLOBE Since the times of the ancient Greeks, people knew the earth was round. In 150 BCE the Greek geometer Crates of Mallus built a world globe ten feet in diameter. Thus for centuries, we have known the shape of Earth, but most people visualize it only as the small, flat area that surrounds them. Contrary to popular legend, Columbus did not envision a flat world, nor did he prove the world was round by sailing to the Americas. LONGITUDE AND LATITUDE Although a globe is round, with no beginning or end, there are two main reference lines from which all distances and locations are calculated. One is the EQUATOR running east and west around the middle of the globe, dividing it into two equal hemispheres. The other is the PRIME MERIDIAN, an imaginary line running from pole to pole and cutting through Greenwich, a section of London, England. Both of these lines are 0° and the globe numbering system starts at the point where they intersect. Locate the equator and prime meridian on the globe. All lines running east and west, parallel to the equator, are called LATITUDE LINES. They are sometimes referred to as parallels because they are parallel to each other. Latitude lines are shown at intervals north and south of the equator. What are the intervals (in degrees) for lines of latitude on your globe? 15o Look at New Orleans on your globe and you will find it located at 30°. Since it is north of the equator, we say it is 30° north latitude, or 30o N. The lines running north and south from pole to pole are called LONGITUDE LINES, or sometimes referred to as meridians. Longitude lines are numbered along the equator on your globe at intervals east and west of the prime meridian at Greenwich., England. What are the intervals (in degrees) for lines of longitude on your globe? 15o Again using New Orleans as an example, we find it located at 90°, or 90° west of 0° longitude. Thus, New Orleans is located at 30o N latitude and 90o W longitude. Find the longitude and latitude of the following cities: Longitude Latitude Boston, MA 71o W 42o N Sydney, Australia 150o E 34o S Tokyo, Japan 140o E 35o N Moscow, Russia 37o E 55o N Baghdad, Iraq 44o E 32o N EARTH’S AXIS Imagine that you are the sun watching the earth revolving about its axis once a day. Looking down from the North Pole, which direction does the earth spin, clockwise or counter-clockwise? How did you determine this? (Hint: Which coast of the United States experiences sunrise first?) Looking down from the North Pole the Earth spins counter-clockwise The East Coast of the US receives sunlight before the West Coast Where in the World 1 Notice that the earth’s axis is not perpendicular with the surface of the table. The axis is tilted in the same direction throughout a year; however, as the Earth orbits the Sun, the hemisphere (north or south of the equator) that is tilted away from the Sun will gradually come to be tilted towards the Sun, and vice versa. This effect is the main cause of the changing seasons. Whichever hemisphere is currently tilted toward the Sun experiences more hours of sunlight each day, and the sunlight at midday also strikes the ground at an angle nearer the vertical and thus delivers more heat. A protractor has been fitted with a string and weight so that the weight will always 90 hang vertically regardless of the tilt of the protractor. When the straight-edge of 0 the protractor is aligned along the earth’s axis the tilt of the earth can be estimated. What is the tilt of the earth’s axis (in degrees)? 23o LINES OF LATITUDE: THE EQUATOR AND THE TROPICS The equator is where the sun is directly overhead at noon on the two equinoxes. For locations in the northern hemisphere, the VERNAL EQUINOX occurs on the first day of spring around March 21, and the AUTUMNAL EQUINOX that occurs on the first day of autumn around September 21. All locations on the earth, regardless of being in the northern or southern hemisphere or at the equator or at the poles, experience 12 hours of daylight and 12 hours of darkness making them equal in length. In addition to the equator, the Tropic of Cancer, and the Tropic of Capricorn are two other significant lines of latitude that lie north or south of the equator. What are their lines of latitude? Tropic of Cancer 23o N Tropic of Capricorn 23o S How do these lines of latitude correspond with the tilt of the earth’s axis that you estimated earlier? The tilt of the Earth’s axis is equal to the latitudes (North or South of the Equator) The tropics are the two lines where the sun is directly overhead at noon on the two SOLSTICES, near June 21 and December 21. The sun is directly overhead at noon on the Tropic of Cancer on June 21. This is the beginning of summer in the Northern Hemisphere and the beginning of winter in the Southern Hemisphere. The sun is directly overhead at noon on the Tropic of Capricorn on December 21. This is the beginning of winter in the Northern Hemisphere and the beginning of summer in the Southern Hemisphere. For locations in the southern hemisphere, what is the date for the summer solstice? December 21 The winter solstice? June 21 For locations in the southern hemisphere, what is the date for the vernal equinox? September 21 The autumnal equinox? March 21 The area bounded by the Tropic of Cancer on the north and Tropic of Capricorn on the south is known as the "TROPICS." This area does not experience seasons because the sun is always high in the sky. Only higher latitudes, north of the Tropic of Cancer and south of the Tropic of Capricorn, experience significant seasonal variation in climate. Where in the World 2 THE POLES The North and South Poles represent the maximum distance either north or south from the equator. At a distance from the poles lie the ARCTIC CIRCLE and ANTARCTIC CIRCLE. Similar to the tropics and the equator these are lines of latitude. What is the latitude of the Arctic Circle and Antarctic Circle? Arctic Circle 67o N Antarctic Circle 67o S How do these lines of latitude correspond with the tilt of the earth’s axis that you estimated earlier? The Arctic/Antarctic Circles are located 23o from the North/South Poles The Arctic Circle marks the southern extremity of the polar day (24 hour sunlit day) of the summer solstice in June and the polar night (24 hour sunless night) of the winter solstice in December. Within the Arctic Circle, the Sun is above the horizon for 24 continuous hours at least once per year, in conjunction with the Arctic's Summer Solstice. Likewise, in conjunction with the Arctic’s Winter Solstice, the Arctic sun will be below the horizon for at least 24 continuous hours. Does Fairbanks, Alaska experience a polar day or night? Explain your reasoning. No. It is located south of the Arctic Circle. Navigating on earth requires knowing your position (longitude and latitude) and the position of where you are going. Modern devices such as GPS receive signals from several satellites circling the globe that triangulate your position using these multiple reference points in space. You can also use a magnetic compass. Locate on your globe the positions of the north and south magnetic poles. What is the approximate longitude and latitude of the north and south magnetic poles? Longitude Latitude Front South Magnetic Pole 63o S 138o E W i n d o w s North Magnetic Pole 83o N 114o W N The needle of the magnetic compass always points to the magnetic north pole. Using the compass determine the direction of magnetic north and draw an arrow indicating the direction of magnetic north on the illustration of the laboratory. SCALE The scale of the globe gives the relationship between length measured on the globe and the corresponding distance on the ground. The amount of REDUCTION that has taken place is normally identified somewhere on the globe commonly referred to as the scale. On most maps, the map scale is represented by a simple fraction or ratio. This type of description of a map's scale is called a fractional scale. For example, a map where one unit (centimeter, meter, inch, kilometer, etc.) on the illustration represents 1,000,000 of these same units on the actual surface of the Earth would have a representative fraction of 1/1,000,000 (fraction) or 1:1,000,000 (ratio). Of these mathematical representations of scale, the ratio form is most commonly found on maps. What is the scale of your globe? 1 : 41,849,600 Where in the World 3 Wrap a string around the globe at the equator and determine the circumference of the globe at the equator in meters. Using the globe’s scale estimate the circumference of the earth in kilometers. Compare your calculation with the known circumference of 24,900 miles or 40,074 km. Approximately 96.0 cm (0.960 m) for the circumference of the classroom globe. 41,859,600 x 0.960 m = 40,185,216 m = 40,185 km (fairly accurate!) The International Space Station orbits the earth approximately 350 km above the surface. How far above the surface of the globe (in centimeters) is the space station orbiting? (Hint: Set up an equivalent ratio of the globes circumference and the earth’s circumference) 96.0 cm / 40,074 km = x cm / 350 km 0.86 cm above the globe The moon orbits the earth at a distance equal to 60 earth radii (approximately 400,000 km).