Page 122 - SST Class 06

by 1 hour. Conversely, if we go westwards,
local time is retarded by 1 hour.

g We may, thus, conclude that places east of
Greenwich see the sun earlier and gain
time, whereas places west of Greenwich see
the sun later and lose time.
g If we know G.M.T., to find local time, we
merely have to add or subtract the differ-
2. If the other meridians are drawn at 30-degree ence in the number of hours from the given
interval, write the values of other meridians longitude.
shown in the given figure east and west of the Local Time
Prime Meridian.
The local time of a place is the time fixed with
3. Draw equator in the given figure and write its
respect to the apparent movement of the sun.
value including the value of the point where it
When the sun is overhead or at the highest point
cuts the prime meridian.
in the sky, it is mid-day (12 noon). The sun then
LONGITUDE AND TIME begins to move down in the sky and the length of
the shadow increases gradually, of different
g Since the earth makes one complete revolu-
meridians time differs.
tion of 360° in one day or 24 hours, it
passes through 15° in one hour or 1° in 4 Why do We have Standard Time?
minutes. The Prime Meridian which passes through Old
g The earth rotates from west to east, so every Royal Observatory at Greenwich in London is 0°
15° we go eastwards, local time is advanced longitude. It is used as a standard measure for

+12 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 +1 +2 +3 +4 +5 +6 +7 +8 +9 +10 +11 +12 -12

PM AM -4 PM AM
Lose one -1 Lose one
calendar day -3 calendar day
-5
+10
+12 -4 +7
-9 0 +1 +11 +12
Monday Sunday 0 +2 +3 +4 +5 +9 Monday Sunday
-10 -8 -7 -4 0 +8 +10 +11 -10
-6 -3.30 +1 +2 +4 +6
-5 -1 +2 +4 +5 +8 +9 +11
International Date Line -11 -11 -10 -5 -4 0 +1 +2 +3 +3.30 +4 +4.30 +5.30 +5.45 +6.30 +10 International Date Line -11

+5
+6
-6
-4
-11
-3.30 -1 0 +3.30 +5.30 +7 +10 +10 +11
+1 +8
12 +3 +5 +8
-10 -5 -5 -2 +4 +10 +11.30
-11 -10 -9.30 -3 0 +3 +5 +7 +9 +12
+12 -9 -4 0 +11
-2 +2 +3
+13 +13
+8 +10 +11.30
+12 +9.30
Prime Meridian +12.45
-3 +10.30
+12.45 +10
Add one -4 Half hour zones Add one
calendar day -2 calendar day
Social Science-6 122