Page 60 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

24 Chapter 1 essentials of Geography
60° W
80° 70° 60° 50° 40°
30°30° 0° E
20° 10°N
0° 10°S 20°
90° E
60° E
especially in large countries. In 1870, a traveller going from Halifax, NS, to Toronto, ON, had to change time at Saint John, NB; Québec City, QC; Montréal, QC; Ottawa, ON; and Toronto, ON. When it was noon in Washington, DC, in the United States, it was 12:54 p.m. in Halifax, 12:14 p.m. in Montreal, and 11:51 a.m. in To- ronto! Today, with six time zones, only five adjustments to clocks are needed when crossing Canada—from New- foundland Standard Time to Atlantic, Eastern, Cen- tral, Mountain, and Pacific Standard Times—and three changes (with four time zones) across the continental United States.
As illustrated in Figure 1.19, when it is 9:00 p.m. in Greenwich, then it is 5:30 p.m. in St. John’s, NL (UTC +3.5 hr), 5:00 p.m. in Halifax, NS (+4 hr), 4:00 p.m. in Toronto, ON (+5 hr), 3:00 p.m. in Winnipeg, MB (+6 hr), 2:00 p.m. in Edmonton, AB (+7 hr), and 1:00 p.m. in Vancouver, BC (+8 hr). To the east, it is midnight in Ar Riyaˉd¸, Saudi Arabia (+3 hr). The designation a.m. is for ante meridiem, “before noon,” whereas p.m. is for post meridiem, “after noon.” A 24-hour clock avoids the use of these designations: 3 p.m. is stated as 15:00 hours; 3 a.m. is 3:00 hours.
As you can see from the modern international time zones in Figure 1.19, national or state boundaries and political considerations distort time boundaries. For example, China spans four time zones, but its government decided to keep the entire country operating at the same time. Thus, in some parts of China clocks are several
30° W
▲Figure 1.18 Earth’s coordinate grid system. latitude and paral- lels and longitude and meridians allow us to locate all places on earth precisely. The red dot is at 49° N latitude and 60° e longitude.
In 1884 at the International Meridian Conference in Washington, DC, the prime meridian was set as the official standard for the world time zone system— Greenwich Mean Time (GMT) (wwp.greenwichmeantime .com/). This standard time system established 24 stan- dard meridians around the globe at equal intervals from the prime meridian, with a time zone of 1 hour span- ning 7.5° on either side of these central meridians. Before this universal system, time zones were problematic,
12 MIDNIGHT
Almaty (Alma Ata)
12:45
12:30 Mumbai
5 A.M.
12 NOON
11 P.M. 12 MIDNIGHT
1 A.M.
3 A.M.
4 A.M.
6 A.M.
7 A.M.
8 A.M.
9 A.M. 10 A.M.
ALASKA Fairbanks
Seward Vancouver
Prime Meridian
International Date Line
Alaska
Pacific Mountain Central Eastern Atlantic Greenland
12:30
2:30
Singapore
2 A.M.
9 P.M. 10 P.M.
Moscow
Jerusalem Cairo
Lagos
Beijing 1:30
Vladivostok Tokyo
Chicago Denver
Mexico City
9:30
Non-standard time
Halifax New York
2:30
Rome
Perth 4:30
Sydney
Wellington
Rio de Janeiro
HAWAII Honolulu
12:30
8:30
Los Angeles
10:30
11:30
11 A.M.
1 P.M. 2 P.M. 3 P.M.
Resolute Thule
4 P.M.
5 P.M.
6 P.M. 7 P.M.
London (Greenwich)
8 P.M.
Edmonton
Churchill
Winnipeg
3:30 Newfoundland time
▲Figure 1.19 Modern international standard time zones. If it is 7 p.m. in Greenwich, determine the present time in Moscow, london, Halifax, Chicago, Winnipeg, Denver, los Angeles, Fairbanks, Honolulu, Tokyo, and Singapore. [Adapted from Defense Mapping Agency.
See aa.usno.navy.mil/faq/docs/world_tzones.html.]