Latitude refers to the angular distance North or South of the equator measured in degrees, minutes and seconds. The equator is given a value of 00. It is an imaginary line which divides the Earth into two hemispheres. The Northern hemisphere has a latitude of 90o N and the Southern hemisphere has a latitude of 90o S. Therefore, Parallels of latitude are particular lines joining all points on the surface of the earth and making an angle of 300 N with the equatorial plane.

**THE IMPORTANT PARALLELS INCLUDE**

- Equator 0
^{o} - Tropic of cancer 23.5 degrees N
- Tropic of Capricorn 23.5 degrees S
- Arctic Circles 66.5 degrees N
- The Atlantic Circle 66.5 degrees S

### LONGITUDE

Refers to the angular distance measured in degrees East and West of the Greenwich Meridian. Prime Meridian is the line running through the poles and the Greenwich observatory near London. It is also known as Greenwich Meridian.

All lines of longitude are semi circles of equal length. Lines of longitude are also called meridians. There are 360 degrees in a circle, 1800 lie east of the Greenwich Meridian and the other 1800 west of Greenwich. The Greenwich lines have been chosen by convention (meaning that any other lines could have served the same purpose).

### CALCULATION OF TIME

The earth rotates on its axis from West to East once every twenty four hours. This means 3600 of longitude are covered in a period of 24 hours or 1 degree in four minutes. Places at a given meridian will experience midday at the same time.

Time recorded along the same meridian is known as local mean time (LMT).

Example:

When the local time of Accra is 2.00pm what will be the local time of Bangui 15 degrees E.

15 degrees – 0 degrees = 15 degrees

15 x 4 minutes = 60

60/60 = 1 hour Accra 2.00 pm + 1.OO hour time difference = 3.00 pm

When the local times of Nairobi 45 degrees E is 10.00am. Find the meridian of Kinshasa where the local time is 9.00am.

10.00am Nairobi – 9.00am Kinshasa = 1.00 hour difference

10 = 4 minutes hours = 60 minutes (60×1) 60 minutes / 4 minutes = 15 degrees 45 degrees E Nairobi â€“ 15 degrees = 300 E Kinshasa

The longitude or Meridian of Kinshasa is 30 degrees E What is the local time at Morogoro-Tanzania when it is noon at Kigali-Rwanda?

Procedure

i. Note the longitudinal position between the two points Kigali 300 E and Morogoro 450 E

ii.Find the difference in degrees of longitude between Kigali and Morogoro 45 degrees – 30 degrees = 15 degrees

iii. Multiply the difference by 4 minutes 150 x 4 minutes = 60 minutes 60 Ã· 60 = 1 hour

iv. The time difference is to be added (+) in case of places to the East of a point. In case of place to the West, the time difference is subtracted (-). Since Morogoro is to the East of Kigali, Morogoro time will be ahead of that of Kigali’s by 1 hour, therefore time for Morogoro will be: 12.00 noon + 1 hour = 1.00 pm. The local time at Morogoro is 1.00pm.

Explain the importance of a Great Circle Importance of a Great Circle

### GREAT CIRCLES

Any circle which divides the globe into hemispheres is a great circle. The equator is a great circle and Greenwich Meridian together with Meridian 1800 make another great circle. The number of great circles is limit less.

### CHARACTERISTICS OF GREAT CIRCLES

i. All great circles divide the earth (sphere) into two hemispheres. ii. A great circle is the largest possible circle that can be drawn on the surface of the sphere. iii. The radius of great circles is the same as the radius of the earth.

### IMPORTANT GREAT CIRCLES

i. All lines of longitudes (Meridians) ii. Equator

### USES OF GREAT CIRCLES

Great circles are used to plot routes for ships crossing the vast oceans and aircraft flying great distance in space. Ships and aircraft travel by following great circles in order to save fuel and time because the shortest route between two places is along the circle of the great circle which passes through them.

**Importance of Parallels and Meridians** Calculate local time Calculating Local time Define time and time zone

**Time and time zone** Time means duration or suitable moment for some purpose. Time zone refers to a zone where standard time is accepted throughout a longitudinal zone 150 in width.

**Essence of time and time zone** The importance of time zones is to avoid the problems in telling time if every place had its own time set according to the local mean time. The timetable of various human activities such as television and radio programs would be confusing if they had to show different times. As the time varies from place to place to place, different stretches of land agreed to adopt the time from certain meridian, that time is known as standard time. East African countries agreed to adopt standard time taken from meridian of 45^{o}E. When a whole stretch of land keeps to the same standard time that stretch of land forms a time zone. ** **

**Variation of standard time in a single country** Large countries like USA, China, etc have several standard time zones with each time zone covering about 15 degrees of longitude. There are 24 times zones in the world. The starting point for dividing the world into 24 times zones is the Greenwich Meridian. The standard time for Greenwich is known as the Greenwich Meridian time (GMT). ** **

**International Date Line** The International Date Line is the line where date is changed or calendar day begins. This line follows approximately the 1800 meridian.

**Locating International Date Line** When the time is 6.00pm on Monday 25th December, at Greenwich, the time at 1800 E longitude will be 12 hours ahead of Greenwich Mean Time. The time at 1800 E will be 6.00am on Tuesday 26th December. Therefore if one travels eastwards and crosses the date line, one will gain a day whereas one who travels westwards across the line will loose a day.

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