The Importance of the Parallels and Meridians

1. Longitude is the angular distance measured in degrees east or west of the Prime Meridian.
2. Lines of longitude, also called meridians, run from the North Pole to the South Pole.

Prime Meridian (Greenwich Meridian)

1. The Prime Meridian is the 0° longitude line, passing through Greenwich, a town in England.
2. It is the reference point from which all other longitudes are measured.
3. Longitudes are measured from 0° to 180° East and 0° to 180° West of Greenwich.

Longitudes

The importance of longitudes and latitudes:

1. They are used by pilots and sailors to guide their paths as they steer the planes and ships.
2. When used together, longitude and latitude define a specific location through geographical coordinates (Fig 1.23). Each location on Earth has its unique latitude and longitude. For example, the location of a point shown on figure 1.23 below is 40°N,60°W.
3. Longitudes enable geographers to calculate the local time of a place, X, given the local time and longitude of place Y, as the point of reference.
4. Latitudes are used as a guide to explain the variation in climate on the surface of the Earth. It is generally known that places along the equatorial belt experience a hot and wet climate for most of the year.

Longitude and time

The earth rotates on its own axis from west to east once every twenty-four hours (one day). This means that the earth turns through 360° in twenty-four hours. All places along a given meridian will experience midday along the same meridian, it is known as Local Mean, on the Greenwich meridian is known as Local Mean Time (LMT).

When it is 12:00 noon on the Greenwich meridian it will be 1:00 pm at a place of 15°E or 11:00 at a place of 15°W. To find time for example for Musoma in Tanzania (34°) when it is 12:00 in Kinshasa Zaire

Time Difference Between Kinshasa and Musoma

Longitude Positions

1. Kinshasa: 15°30′ E
2. Musoma: 34°00′ E

Difference in Longitude

$34^\circ00' - 15^\circ30' = 18^\circ30'$

Which is: $18.5^\circ$

Converting Longitude Difference to Time

Earth rotates $360^\circ$ in 24 hours, so:

1. 1 hour = 15°
2. 1° = 4 minutes

Therefore: $18.5^\circ \times 4 = 74$ minutes 74 minutes = 1 hour and 14 minutes

Which Place is Ahead?

Musoma (34°E) is east of Kinshasa (15°30′E), so it is ahead in time.

Conclusion: Musoma is 1 hour and 14 minutes ahead of Kinshasa.

Great circle

The intersection of the surface of a sphere and a plane through its centers for example meridians of longitude and equator is a great circle in the earth's surface. Therefore, there is no limit to the number of great circles that can be drawn

1. The great circles are important for aero planes, which use them as route ways to guide their path
2. Great circles are important for ship to follow routes along great circles

1. Time refers to a period used to measure when an event or activity occurs.
2. It is measured in:
   • Seconds
   • Minutes
   • Hours
   • Days
   • Months
   • Years

1. A Time Zone is a region that shares the same standard time.
2. Standard Time is the official time adopted for a specific area or country.

Example of a time zone

East African Standard Time (E.A.S.T) is used by:

1. Tanzania
2. Kenya
3. Uganda
4. Ethiopia
5. Djibouti
6. Somalia

These countries all follow the same time zone to simplify timekeeping and coordination.

Importance of time zones

1. If every place used local mean time, there would be a lot of confusion.
   • Especially in railway and airway schedules.
   • Radio and TV programs would also face issues with different local times.

To avoid such problems, countries in the same longitudinal stretch adopt a common standard time, usually based on a major meridian.

Greenwich Mean Time (GMT)

Essence of time zone

In a certain place there could be a place on the surface using its own local time. This would bring a lot of confusion example every radio station would have to announce different times for every region within the same country: Local time of Bukoba would be different from that of Dodoma.

1. The above confusion was avoided when it was internationally agreed to split the world into 24 time zone according to Longitudes
2. The longitudinal division across the earth with an approximates with of 15 of longitude which is regular across the oceans.
3. Each time zone has a standard time, which is the time of the longitude (meridian near the center of time zone. In the same way, all countries belonging to the same time zone have common time.

Examples

1. If it is 9:30 am at Kase 33°15°E what time is in Zanzibar 45°15°E?

   Time Difference Between Kase and Zanzibar Longitudes

   1. Kase: 33°15′ E
   2. Zanzibar: 45°15′ E

   Difference in Longitude

   $45^\circ15' - 33^\circ15' = 12^\circ$

   Time Difference

   Since 1° = 4 minutes: $12^\circ \times 4 = 48 \text{ minutes}$

   Time Adjustment

   Zanzibar is east of Kase, so it is ahead in time. Kase: 9:30 AM $9:30 + 48 \text{ minutes} = 10:18 \text{ AM}$

   Conclusion

   If it is 9:30 AM at Kase, it is 10:18 AM in Zanzibar.

2. Find the time for the Younce 30°W if it is 12.00 noon London

   Time at Younce (30°W)

   Given

   1. London: 0° longitude
   2. Younce: 30°W longitude
   3. Time in London: 12:00 noon

   Longitude Difference

   $30^\circ - 0^\circ = 30^\circ$

   Time Difference

   $30^\circ \times 4 = 120 \text{ minutes} = 2 \text{ hours}$

   Direction of Time

   Younce is west of London → it is behind in time. $12:00 \text{ noon} - 2 \text{ hours} = 10:00 \text{ AM}$

   Conclusion

   If it is 12:00 noon in London, it is 10:00 AM in Younce.

3. When it is 3.30 pm at Nairobi (25°E) what is the time for Comoro 120°E?

   What is the time in Comoro when it is 3:30 PM in Nairobi?

   Longitudes

   1. Nairobi: 25°E
   2. Comoro: 120°E

   Longitude Difference

   $120^\circ E - 25^\circ E = 95^\circ$

   Time Difference

   $95^\circ \times 4 = 380 \text{ minutes} = 6 \text{ hours and } 20 \text{ minutes}$

   Time Adjustment

   Comoro is east of Nairobi, so it is ahead in time. $3:30 \text{ PM} + 6 \text{ h } 20 \text{ min } = 9:50 \text{ PM}$

   Conclusion

   If it is 3:30 PM in Nairobi, it is 9:50 PM in Comoro.

International Date Line

The line where date is changed or where the calendar day begins.

The standard time zones of the world