The United States
covers six time zones: Eastern,
Central, Mountain, Pacific, Alaska, and Hawaii-Aleutian.
US territories cover four more time zones. Russia covers
11 time zones.
In order to accommodate
local geography, the boundaries indicating
actual time zones are not straight lines.
Some US states,
such as Indiana, are in two time zones.
Two US territories, Guam
and Wake Island, are on the other side of the
International Date Line from North America.
In the US, Daylight
Saving Time, which first originated during
World War I, begins at 2:00 AM on the first Sunday in
April and ends at 2:00 AM on the last Sunday in October.
Hawaii and Arizona
do not observe Daylight Saving Time.
A 24-hour clock
is used by the military and most scientists.
In the 24-hour time system, the hours are numbered from
0 to 23, and there are no AM and PM designations. With
this time system, 0 oclock
A typical time zone differs from its neighboring
zones by one hour, but some time
zones differ by a fraction of an hour. For
example, the time on the Canadian island of St. Johns
differs from that in the rest of Newfoundland by 30
minutes. The time in Nepal differs from neighboring
India by 15 minutes.