Page 37 - Longitude and Time Zones
TIME ZONES:
The Earth rotates around its axis once every 24 hours =
24 time zones around the Earth, each 1 hour apart.
The Earth rotates through 360 degrees in 24 hours,
therefore it must rotate through 15 degrees of longitude
in 1 hour
Therfore, each of the 24 time zones is 15 degrees wide.
Every place within a time zone has the same time, called
standard time.
History of time zones – 2nd paragraph – p 37
The prime meridian is the center of a time zone that
extends 7.5 degres on either side. (fig 3-8). Time in this
zone is called universal time (UT) and the standard times
in the other zones are compared to it. Every 15 degrees,
on either side of the prime meridian, is the centre of the
time zone.
Universal time was formerly called Greenwich Mean Time
(GMT). Some people still refer to time in this zone at
GMT.
Grade 10 Geo – Chapter 3 – A. Robinson – October 2006
1
Page 38 cont.
Time zones that are east of the prime meridian have local
times that are ahead of UT. (therefore, west = behind) –
look at figure 3-9.
Countries may modify the shape of the time zone and the
standard time they use (ex. China has 1 standard time for
the whole country which covers more than 60 of
longitude). Canada has 6 time zones.
Question – why would countries modify the
shapes of the time zones?
The boundaries of the time zones do not exactly follow
the meridians of longitude.
International Date Line – page 39
The International Date Line runs between the North and
South Pole, and generally follows the 180 line of longitude
through the Pacific Ocean.
If you cross the dateline moving westward, you add a day.
If you cross the date line moving eastward, you lose a
day.
Time does not change unless the date line corresponds to
a time zone boundary. (This means that on one side of
the line it might be 2pm on Friday, and on the other side
of the line it would be 2pm on Thursday.)
Grade 10 Geo – Chapter 3 – A. Robinson – October 2006
2
Daylight-Saving Time
Daylight-saving time is used during the summer to extend
daylight hours into the evening, and helping to reduce
energy since lights don’t have to be turned on until later
in the day. (ex. The sun would set at 9pm, instead of 8pm)
In Canada and the US, daylight-saving time begins on the
first Sunday in April and ends on the last Sunday in
October. Other countries use different dates.
Remember the saying “spring forward, fall back”.
Longitude and Time – p 39-40
Early sailors determined their latitude by the angle of
the sun above the horizon or by the position of the North
Star (Polaris), but they had no practical way to find their
longitude.
In theory, longitude could be calculated if sailors knew
their local time and the time in Greenwich. However, the
pendulum clocks that were in use at the time did not work
on a ship being tossed about by waves.
In 1735, John Harrison, a British inventor, developed his
first marine chronometer. It was a highly accurate
spring-loaded clock that could keep time on a moving ship.
See p 40 – how longitude was calculated.
Do questions 1-8, 11-18 on pages 40-42
Grade 10 Geo – Chapter 3 – A. Robinson – October 2006
3