Page 61 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 1 essentials of Geography 25
hours off from what the Sun is doing. In Canada, parts of eastern Quebec and northwestern Ontario are in the same time zone.
Coordinated Universal Time For decades, GMT was determined using the Royal Observatory’s astronomical clocks and was the world’s standard for accuracy. How- ever, Earth rotation, on which those clocks were based, varies slightly over time, making it unreliable as a basis for timekeeping. Note that 150 million years ago, a “day” was 22 hours long, and 150 million years in the future, a “day” will be approaching 27 hours in length.
The invention of a quartz clock in 1939 and atomic clocks in the early 1950s improved the accuracy of measuring time. In 1972, the Coordinated Universal Time (UTC)* time-signal system replaced GMT and be- came the legal reference for official time in all coun- tries. UTC is based on average time calculations from atomic clocks collected worldwide. You might still see official UTC referred to as GMT or Zulu time.
International Date line An important corollary of the prime meridian is the 180° meridian on the opposite side of the planet. This meridian is the International Date Line (IDL), which marks the place where each day of- ficially begins (at 12:01 a.m.). From this “line,” the new day sweeps westward. This westward movement of time is created by Earth’s turning eastward on its axis. Locat- ing the date line in the sparsely populated Pacific Ocean minimizes most local confusion (Figure 1.20).
At the IDL, the west side of the line is always one day ahead of the east side. No matter what time of day it is when the line is crossed, the calendar changes a day (Figure 1.20). Note in the illustration the departures from the IDL and the 180° meridian; this deviation is due to local administrative and political preferences.
Daylight Saving Time In 70 countries, mainly in the temperate latitudes, time is set ahead 1 hour in the spring and set back 1 hour in the fall—a practice known as daylight saving time. The idea to extend daylight for early evening activities at the expense of daylight in the morning, first proposed by Benjamin Franklin, was not
*UTC is in use because agreement was not reached on whether to use English word order, CUT, or the French order, TUC. UTC was the compromise and is recommended for all timekeeping applications; use of the term GMT is discouraged.
North Pole
Aleutian Is.
60°N
Sunday
Earth’s rotation
Monday Add a day
South Pole
0° Equator
20°S
40°S
▲Figure 1.20 international Date line. The IDl location is approxi- mately along the 180th meridian (see Figure 1.19). The dotted lines on the map show where island countries have set their own time zones, but their political control extends only 3.5 nautical miles (4 mi) offshore. Officially, you gain 1 day crossing the IDl from east to west. (See GeoReport 1.5)
adopted until World War I and again in World War II, when Great Britain, Australia, Germany, Canada, and the United States used the practice to save energy (1 less hour of artificial lighting needed).
In 1986 and again in 2007, the United States and Canada increased daylight saving time. Time “springs forward” 1 hour on the second Sunday in March and “falls back” 1 hour on the first Sunday in November, except in a few places that do not use daylight saving time (such as Saskatchewan, Arizona, and Queensland, Australia). In Europe, the last Sundays in March and October are used to begin and end the “summer-time period” (see webexhibits .org/daylightsaving/).
Maps and Cartography
For centuries, geographers have used maps as tools to display spatial information and analyze spatial relation- ships. A map is a generalized view of an area, usually some portion of Earth’s surface, as seen from above and greatly reduced in size. A map usually represents a spe- cific characteristic of a place, such as rainfall, airline
Subtract a day
60°S 180th Meridian
40°N 20°N
Georeport 1.4 The World’s Most Accurate Clock
Time and Frequency Services of the National Institute for Standards and Technology (NIST), U.S. Department of Commerce, operates several of the most advanced clocks currently in use. The NIST-F1 cesium atomic clock is the
most accurate clock in the world. Housed in Boulder, Colorado, it will not gain or lose a second in nearly 20 million years. In Canada, the Institute for Measurement Standards, National Research Council of Canada, participates in determining UTC. For the official time in Canada in your time zone, see www.nrc-cnrc.gc.ca/eng/services/time/web_clock.html.
International Date Line
140°W
120°W
160°W
160°E
140°E