geographic grid : latitudes and longitudes

geography chapter 2

describe lines of latitude.

• they are the imaginary lines joining all places having the same latitude towards north or south of the equator.

• latitude is the angular distance of a place north of south of the equator.

• latitude is marked in degrees, with equator being 0 degrees.

• as the lines of latitude are parallel to each other, they are called parallels of latitude.

• each parallel of latitude is a circle, therefore the equator is great circle.

• the lines of latitude are not of equal length and become smaller as we move toward the poles.

what are the main latitudes?

• there are 181 parallels of latitude at 1° interval.

• equator - longest line of latitude. represents 0° latitude.

• north pole - located at angular distance of 90°N of the equator.

• south pole - located at angular distance of 90°S of the equator.

• tropic of cancer - located at 23 ½ °N of the equator.

• tropic of capricorn - located at 23 ½ °S of the equator.

• arctic circle - 66 ½ °N latitude, marks the limit of north polar region.

• antarctic circle - 66 ½ °S latitude, marks the limit of south polar region.

briefly describe the northern and southern hemisphere.

• the equator runs midway between the poles and divides the earth into 2 equal hemispheres - northern and southern.

• the north and south poles are opposite to each other at extreme ends of the sphere - located at 90° angular distance north or south of the equator.

• length of equator = circumference of the earth = 40075 km.

what are the two uses of latitudes?

• finding locations of places - latitudes give us the location of a place north of south of the equator. such a location is called an absolute location.

• measuring distances of places - distances are calculated with reference to equator at right angle to the place.

what are heat zones?

• lines of latitude divide the earth into distinct heat belts.

• the lines of latitude indicate the general climate of the area by applying the principle of heat zones/thermal zones of the earth.

• the 3 heat zones are: the torrid/tropical zone, the temperate zones and the frigid zones.

describe the torrid/tropical heat zone.

• the area lying between the tropic of cancer and tropic of capricorn are the limits of the tropical zone.

• it is the hottest zone of the earth.

describe the temperate zones.

• between the arctic circle and the tropic of cancer as well as between the antarctic circle and tropic of capricorn lie the two temperate zones.

• north temperate zone (23 ½ °N to 66 ½ °N) and south temperate zone (23 ½ °S to 66 ½ °S)

• the climate is moderate, neither too hot nor too cold.

describe the frigid zones.

• between the arctic circle and the north pole as well as between the antarctic circle and the south pole lie the two frigid zones.

• these zones are polar regions.

• they receive slanting rays from the sun.

• very low temperatures are recorded.

describe lines of longitude.

• a longitude is the angular distance of a place east or west of the prime meridian.

• prime meridian - line of longitude whose angular distance is 0°. passes through greenwich near london.

• lines to the west of greenwich are suffixed with °W and those east of greenwich are suffixed with °E.

• there are a total of 360 lines at 1° interval.

• lines of longitude are also called meridians of longitude.

• meridian is derived from the latin word meridianum meaning noon. the sun crosses a meridian at noon. all places on a particular meridian will have noon at the same time.

• all lines of longitude converge at the poles and are thus of equal length.

describe the eastern and western hemispheres.

• the prime meridian together with the 180° longitude divides the earth into eastern and western hemispheres.

• however, any two diametrically opposite lines can also divide the earth into two equal hemispheres.

differentiate between lines of latitude and lines of longitude.

latitude

1. a latitude is the angular distance of a place north or south of the equator.

2. lines of latitude are parallel to the equator and each other.

3. each line of longitude is a full circle. they are not of equal length and become smaller moving toward the poles.

4. latitude degrees are measured from the equator to its north or south.

longitude

1. a longitude is the angular distance of a place east or west of the prime meridian.

2. lines of longitude converge at the poles.

3. all lines of longitude are semicircles and are equal in length.

4. longitude degrees are measured from the prime meridian to its east or west.

describe local time.

• the local time of any place is obtained by the overhead sun at noon.

• for each degree of longitude, the local time varies by 4 minutes.

• for eg, the longitude of mumbai is 73°E and that of delhi is 77°E. if it is 12 noon at mumbai, it must be 16 minutes past 12 noon in delhi because of the 4° longitude difference.

• every place at a different longitude will have its own local time.

describe time zones.

• earth has been divided into 24 time zones according to the number of hours in a day.

• each zone covers 15° longitude.

• the time for the whole zone is determined by the central meridian of that place.

• countries with smaller east-west extent like india have only one standard time zone, but others like russia, canada, USA have more than one time zone.

what is standard time?

• the uniform time based on a central meridian is known as standard time.

• standard time must always be divisible by 7 ½°.

• this allows time to be reckoned by a unit of half an hour and not smaller differences.

what is greenwich mean time?

• the time at greenwich (0° longitude) has been selected as the mean time.

• thus, if it is 12 noon at greenwich - at 15°E, it will be 1pm. at 30°E, it will be 2pm.

• the time fixed with greenwich is called greenwich mean time or GMT.

what is indian standard time?

• in india, 82°30’E is the central meridian.

• it passes through mirzapur near allahabad.

• it is known as standard meridian of india.

• while fixing IST to GMT, we have to add 330 minutes or 5 ½ hours as india is 5 ½ hours ahead of GMT.

what is the international date line?

• the line of longitude 180° is the same for east and west of the prime meridian.

• it is diametrically opposite to the greenwich meridian, hence it causes a time difference of a full day on crossing the line.

• thus, on crossing the line, a day is gained or lost.

• the international date line (IDL) is the 180° line.

• to avoid confusion of different dates within the same country, the date line bends and goes zig-zag at the bering strait between siberia and alaska and at fiji, tonga, new zealand and some other islands.

what are great and small circles?

• a great circle is a circle that is drawn on the surface of a sphere that has a radius equal to the radius of the sphere, and whose centre is also the sphere’s centre.

• the equator is the only latitude that is a great circle.

• all longitudes are a part of a great circle.

• circles which do not pass through the centre of the earth are called small circles.

• all the lines of latitude other than the equator are small circles.

• arcs of great circles are the shortest route between two points on a sphere.

what are the characteristics of a great circle?

1. a great circle is a theoretical circle formed by the intersection of the earth’s surface and an imaginary plane that passes through the centre of the earth and divides it into 2 equal parts.

2. all such circles must pass through or touch the centre of the circle.

3. infinite number of circles that touch the two opposite ends of the sphere can be drawn on a sphere.

4. intersecting great circles always bisect each other.