Latitude and Longitude including important Parallels and Meridians
Latitude and longitude, coordinate system by means of which the position or location of any place on Earth’s surface can be determined and described.
Latitude
- The latitude is the angle formed by a line going from the center of the earth to the equator at the point on the equator that is closed to the point of interest and another line that goes from the center of the earth to the parallel that goes through the point of interest.
- Latitude is a measurement on a globe or map of location north or south of the Equator.
- Lines joining places with the same latitudes are called parallels ie the lines running East to West are called “Parallels” or “lines of latitude”
- Technically, there are different kinds of latitude—geocentric, astronomical, and geographic (or geodetic)—but there are only minor differences between them.
- In most common references, geocentric latitude is implied.
- Given in degrees, minutes, and seconds, geocentric latitude is the arc subtended by an angle at Earth’s centre and measured in a north-south plane poleward from the Equator. Therefore, the greatest possible latitudes are 90° N and 90° S.
- The value of equator is 0° and the latitude of the poles are 90°N and 90°S.
- If parallels of latitude are drawn at an interval of one degree, there will be 89 parallels in the northern and the southern hemispheres each.
- The total number of parallels thus drawn, including the equator, will be 179.
- Depending upon the location of a feature or a place north or south of the equator, the letter N or S is written along with the value of the latitude.
- If the earth were a perfect sphere, the length of 10 of latitude (a one degree arc of a meridian) would be a constant value, i.e. 111 km everywhere on the earth.
- This length is almost the same as that of a degree of longitude at the equator.
- But to be precise, a degree of latitude changes slightly in length from the equator to the poles.
- While at the equator, it is 110.6 km at the poles, it is 111.7 km.
- Latitude of a place may be determined with the help of the altitude of the sun or the Pole Star.
- As aids to indicate different latitudinal positions on maps or globes, equidistant circles are plotted and drawn parallel to the Equator and each other; they are known as parallels, or parallels of latitude.
- In contrast, geographic latitude, which is the kind used in mapping, is calculated using a slightly different process.
- Because Earth is not a perfect sphere—the planet’s curvature is flatter at the poles—geographic latitude is the arc subtended by the equatorial plane and the normal line that can be drawn at a given point on Earth’s surface.
- The length of a degree of arc of latitude is approximately 111 km (69 miles), varying, because of the nonuniformity of Earth’s curvature, from 110.567 km (68.706 miles) at the Equator to 111.699 km (69.41 miles) at the poles.
- Geographic latitude is also given in degrees, minutes, and seconds.
Important Parallels of latitude
- The equator
- The Tropic of Cancer (23½ºN)
- The Tropic of Capricorn (23½ºS)
- The Arctic Circle (66½ºN)
- The Antarctic Circle (66½ºS)
Longitude
- Longitude is a measurement of location east or west of the prime meridian at Greenwich, the specially designated imaginary north-south line that passes through both geographic poles and Greenwich, London.
- Unlike the parallels of latitude which are circles, the meridians of longitude are semi-circles that converge at the poles.
- If opposite meridians are taken together, they complete a circle, but, they are valued separately as two meridians.
- The meridians intersect the equator at right angles.
- Unlike the parallels of latitude, they are all equal in length.
- For convenience of numbering, the meridian of longitude passing through the Greenwich observatory (near London) has been adopted as the Prime Meridian by an international agreement and has been given the value of 0°.
- The longitude of a place is its angular distance east or west of the Prime Meridian. It is also measured in degrees.
- The longitudes vary from 0° to 180° eastward and westward of the Prime Meridian.
- The part of the earth east of the Prime Meridian is called the eastern hemisphere and in its west referred to as the western hemisphere
- The vertical lines running north-south, join the two poles. They are called the meridians of longitude. They are spaced farthest apart at the equator and converge at a point at each pole.
- Measured also in degrees, minutes, and seconds, longitude is the amount of arc created by drawing first a line from Earth’s centre to the intersection of the Equator and the prime meridian and then another line from Earth’s centre to any point elsewhere on the Equator.
- Longitude is measured 180° both east and west of the prime meridian.
- As aids to locate longitudinal positions on a globe or map, meridians are plotted and drawn from pole to pole where they meet.
- The distance per degree of longitude at the Equator is about 111.32 km (69.18 miles) and at the poles, 0.
Longitude and Time
- We all know that the earth rotates from west to east over its axis.
- It makes the sun rise in the east and set in the west.
- The rotation of the earth over its axis takes 24 hours to complete one circle or 360° of longitudes.
- As 180° of longitudes fall both east and west of the Prime Meridian, the sun, thus takes 12 hours’ time to traverse the eastern and western hemispheres.
- In other words, the sun traverses 150 of longitudes per hour or one degree of longitude in every four minutes of time.
- It may further be noted that the time decreases when we move from west to east and increases with our westward movement.
- The rate of the time at which the sun traverses over certain degrees of longitudes is used to determine the local time of an area with respect to the time at the Prime Meridian (0°Longitude).
Important Meridians of Longitude
- Prime meridian
- International Date line
Importance of Parallels and Meridians
- The combination of meridians of longitude and parallels of latitude establishes a framework or grid by means of which exact positions can be determined in reference to the prime meridian and the Equator: a point described as 40° N, 30° W, for example, is located 40° of arc north of the Equator and 30° of arc west of the Greenwich meridian.
