Presentation is loading. Please wait.

Presentation is loading. Please wait.

Where on Earth are You?.

Similar presentations

Presentation on theme: "Where on Earth are You?."— Presentation transcript:

1 Where on Earth are You?

2 Latitude and longitude
Measured in degrees, minutes, seconds 1 degree = 60 minutes (1° = 60’) 1 minute = 60 seconds (1’ = 60’’) Nautical mile (nm) 1 nm = 1’ of arc length of latitude 1 nm = 1’ of arc length of longitude at the equator

3 Latitude and longitude
Latitudes (or parallels) are parallel to the equator 0 to +90° Northern Hemisphere 0 to -90° Southern Hemisphere Small circles Longitudes (or meridians) are formed at right angles to the latitude lines Measured from the Prime Meridian 0 to 360° East from the Prime meridian Or, 0 to +180°E and 0 to -180°W International date line Great circles

4 Latitude North Pole 60°N 30°N Latitude 0° Equator 30°S South Pole
(b) Latitude is measured as the angle between a line from Earth’s center to the equator and a line from Earth’s center to the measurement point.

5 Measuring latitude – North Star, Polaris
30° Polaris is directly overhead at the North Pole (90° of latitude); in other words, the angle between Polaris and the horizon at the North Pole is 90°. This angle is called "the altitude" of Polaris. At the Equator (0° of latitude), the North Star is on the horizon, making an angle of 0°. For any point between the Equator and the North Pole, latitude is obtained simply by measuring the altitude of Polaris: at 30°N the star is 30° above the horizon, at 63°N, it is 63° above the horizon, and so on.

6 Accurate angle measurement evolved over the years
Accurate angle measurement evolved over the years. One simple method is to hold the hand above the horizon with your arm stretched out. The width of the little finger is an angle just over 1.5 degrees elevation at extended arms length and can be used to estimate the elevation of the sun from the horizon plane and therefore estimate the time till sunset. The need for more accurate measurements led to the development of a number of increasingly accurate instruments, including the kamal, astrolabe, octant and sextant. The sextant and octant are most accurate because they measure angles from the horizon, eliminating errors caused by the placement of an instrument's pointers, and because their dual mirror system cancels relative motions of the instrument, showing a steady view of the object and horizon. Navigators measure distance on the globe in degrees, arcminutes and arcseconds. A nautical mile is defined as 1852 meters, but is also (not accidentally) one minute of angle along a meridian on the Earth. Sextants can be read accurately to within 0.2 arcminutes. So the observer's position can be determined within (theoretically) 0.2 miles, about 400 yards (370 m). Most ocean navigators, shooting from a moving platform, can achieve a practical accuracy of 1.5 miles (2.8 km), enough to navigate safely when out of sight of land.[

7 Determining Longitudes
North Pole Reference: Prime meridian Longitude 60°W South Pole at Greenwich (c) Longitude is measured as the angle between a line from Earth’s center to the measurement point and a line from Earth’s center to the prime (or Greenwich) meridian, which is a line drawn from the North Pole to the South Pole passing through Greenwich, England.

8 Longitude and time Use of clocks to record the time the Sun is at its zenith Greenwich Mean Time (GMT) or Universal Time Earth rotates 15° of longitude each hour It does not depend on the speed of the ship, actually, because the chronometer is still useful even when the ship is not moving.  Someone on the ship makes an observation of the position of the Sun, say at noon. Because Earth rotates, points on the surface at different longitudes will face the Sun at different times of the day. The chronometer is set to show the time in a standard location (such as Greenwich), and to keep time very accurately and precisely. When the ship is away from Greenwich, then when it is noon with respect to the ship, it is not noon at Greenwich. The amount of difference of time, as shown by the chronometer, translates into how far around the Earth the ship is.  Suppose that the ship observes noon when the chronometer shows 3 pm. Then the Earth has rotated 3/24 = 1/8 of the way eastward since it was noon at Greenwich. The circumference of Earth is computed according to the latitude (which is easy to determine with an instrument such as a sextant). 1/8 of the circumference of the circle at that latitude is then the distance west of Greenwich.  If the chronometer shows some time in the morning when it is noon at the ship, then the ship is some distance east of Greenwich; the longitude is computed in the same way as before. The earth is rotating at 15degrees longitude per hour or 360degrees per day!  So an accurate clock gives time difference to greenwich compared to local time  eg sun overhead at midday  from this time difference we calculate degrees from greenwich  which is the longitude!

9 Time Zones

10 (Samoa changes time zone)
How did the Republic of Kiribati become the first country to enter the new millenium? By shifting the International Date Line more than 2,000 miles east. So that it will be 2000 in Kiribati while it's still 1999 in Hawai'i.The international date line drawn north and south through the Pacific Ocean may be an imaginary line, but the dispute over where it's drawn is very real. Many South Pacific islands are jockeying for position along the international date line, in a struggle to be the first place on Earth where each calendar day begins — and each New Year. Each contestant wants to be able to say, "The Year 2000 starts here!" At stake is a mix of international travel dollars and pure novelty. Bill Paupe, Kiribati's honorary consul, says, "Everybody is making a case that they are first, and, of course, they've been able to sell that to a number of people." The islands that are promoting themselves as official millennium sites are the Catham Islands east of New Zealand, Tonga, Fiji and Kiribati. Which island will be the first to officially celebrate Jan. 1, 2000, is debatable. The National Geographic Society recognizes the Catham Islands east of New Zealand as the first inhabited place to see each sunrise. But, the Tongan government has considered implementing daylight-saving time to beat the Catham Islands to the millennium. However, Tonga pulled out and remains one hour behind the finish line. Fiji, on the other hand, claims to be the leader of the Pacific pack since it straddles the 180th meridian, which was designated as the halfway point around the globe in Fiji's Daily Post reported in January that the New York-based Millennium World Time Zone organization insisted, "It's official. Fiji will be the first country in the world to enter the third millennium." Even Gisborne, New Zealand, enters the race as first city to celebrate the new millennium. Finally, there's Kiribati (pronounced KIR-ee-bas). Kiribati's island chain spreads over 2,000 miles of ocean — the span of Western Europe — but its 33 atolls cover less area than London. Prior to Jan. 1, 1995, Kiribati had two main island groups on each side of the date line. Consequently, the local time difference between the two groups was 23 hours — same island chain, two different dates. To simplify business and government work — and possibly to chase the new millennium, Kiribati "bent" the international date line to include its easternmost land mass, Caroline Island, which, not coincidentally, has been renamed Millennium Island. "We [Kiribati's consul] are adhering to the Royal Greenwich Observatory, which is the designated world authority on the time zones, and it has said that Millennium Island would be the first to experience the dawn of the new millennium," Paupe said. Can countries simply "spring forward or fall back" in time, and change where the international date line falls? "Yes," says Robert Kiste, director of the Center for Pacific Island Studies at the University of Hawai'i. "They can, it's up to each country to determine its own time zone." So hypothetically, could Hawai'i enter the millennium race by stretching the international date line as far as the Polynesian Islands? "Yes! There's no international law or treaty that prohibits countries from changing their time zones," Paupe said. Some millennium tourists are heading toward the Catham Islands, New Zealand or Kiribati's Christmas Island. Ironically, there are no visitor facilities of any kind on Millennium Island. Actually, it's uninhabited. "People want to book tickets to the island,'' Paupe sighs, "but they don't believe me when I tell them there are no accommodations there." "To me, I just don't see what all the hoopla is about — frankly," Paupe admitted. "What difference is it going to make to our lives, besides this so-called computer glitch? It's not going to change your livelihood, it isn't going to change the environment, it's not going to change anything. The next day the sun is going to come up again and then it will all be forgotten." What about those who are reluctant to leap into the new millennium? Where can they go to celebrate? Well, Samoa remains unchallenged in its bragging rights as the last place on Earth to celebrate the closing of the century. (Samoa changes time zone)

11 East Increase – West Less (1 hr per l5°)
If it 9 p.m. at Position D, what time is it at position C? Position B? If it is 1 p.m. at Position X, at which location is the time 5 p.m.

12 Earth rotates west to east Solar time is based on the position of the sun NIGHT IS FALLING ON EARTH
Look at the East Coast of the United States. The lights are already lit. California the sun is still visible.

13 This pictures shows AMERICAN CITIES at night.

14 Waikiki

Download ppt "Where on Earth are You?."

Similar presentations

Ads by Google