NCERT Class 6 - The Earth Our Habitat, Chapter 2 • NCERT Class 11 - India Physical Environment

Latitudes, Longitudes and Time

Any point on the earth can be located by two numbers - its latitude, the angular distance north or south of the Equator, and its longitude, the angular distance east or west of the Prime Meridian. Longitude also fixes time.

Latitudes

• Latitudes are parallels; they run east to west, are parallel to each other, and never meet.
• The Equator is 0 degrees and divides the earth into the northern and southern hemispheres; it is the longest parallel.
• Parallels get shorter towards the poles, which are points at 90 degrees north and south.
• One degree of latitude is roughly 111 kilometres on the ground.

• Heat zones - the torrid zone between the two tropics gets vertical sun rays at least once a year; the temperate zones between the tropics and the polar circles get slanting rays; the frigid zones beyond the polar circles get extremely slanting rays and are very cold.
• India's latitudinal extent is about 8 degrees 4 minutes north to 37 degrees 6 minutes north, and the Tropic of Cancer passes through the middle of the country, which is why the south is tropical and the north subtropical.

Longitudes and time

• Longitudes are meridians; they run north to south, converge at the poles, and are all of equal length.
• The Prime Meridian at 0 degrees passes through Greenwich near London, and the earth is divided into the eastern and western hemispheres from it.
• There are 360 meridians in all - 180 east and 180 west, meeting at the 180 degree meridian.
• The earth rotates 360 degrees in 24 hours, so it turns 15 degrees in one hour and 1 degree in four minutes.
• Places east of a given meridian are ahead in time, and places to the west are behind.
• The International Date Line roughly follows the 180 degree meridian, bending to avoid land. Crossing it eastward you repeat a day; crossing westward you lose a day.

Indian Standard Time

• A country wide enough to span several meridians must choose a standard meridian so that one time applies throughout.
• India's standard meridian is 82 degrees 30 minutes east, which passes near Mirzapur in Uttar Pradesh.
• Indian Standard Time is five and a half hours ahead of Greenwich Mean Time.
• India's longitudinal extent is about 68 degrees 7 minutes east to 97 degrees 25 minutes east, a span of about 30 degrees, so the sun rises about two hours earlier in the east than in the far west.
• Large countries such as Russia, Canada and the United States use several time zones because one standard time would be impractical.