Concepts of Great Circle, Latitude, Longitude and International Date Line | Geography Notes PDF in English
Great Circle
- Shortest distance between two points on sphere is called great circle- Earth example:
- Equator = great circle among latitudes, because in case of Sphere division, if Halved through center then, Circumference = largest sphere circle.
- All Longitudes = half great circles.
Latitude
- Latitude is how far a point on Earth is from the center, in degrees. It goes from 0 to 90° North and 0 to 90° South.- Latitudes are like circles that run parallel to the equator. The equator is halfway between the poles. These circles are called parallels of latitude. Latitudes also help understand temperature changes: as you move towards the poles, it gets colder.
- Important latitudes are:
- Equator (0°)
- Tropic of Cancer (about 23½° North)
- Tropic of Capricorn (about 23½° South)
- Arctic Circle (about 66½° North)
- Antarctic Circle (about 66½° South)
- Between Tropic of Cancer and Tropic of Capricorn, the midday sun is right overhead at least once a year. This area gets the most heat and is called the Torrid Zone (like a hot tropical area).
- In the northern hemisphere, areas between Tropic of Cancer and Arctic Circle, and in the southern hemisphere, between Tropic of Capricorn and Antarctic Circle, have moderate temperature. These are called Temperate Zones (kind of mild climate).
- Areas around the Arctic Circle and North Pole, and around the Antarctic Circle and South Pole, are the Frigid Zones. It's super cold here because the sun doesn't rise above the horizon.
Longitude
- Longitude is like a distance measured in degrees along the equator, either east or west of the Prime Meridian (0°). It ranges from 0 to 180° E and 0 to 180° W. It's also linked to time.- Longitudes split Earth into two halves, so they're called Great circles. Each longitude crosses every latitude at 90°.
- 1° longitude equals 4 minutes of time. So, 15° = 1 hour.
- Longitudes are like half circles from pole to pole, cutting through the equator.
- Prime Meridian is at 0°. It's called Greenwich line, going through Greenwich near London where the Royal Observatory is.
- Longitudes have an important job: they decide Local Time compared to Greenwich Mean Time (GMT).
- Local Time = noon-sun time in a place.
- Standard Time = Local Time of a country's Standard Meridian.
- India's Standard Meridian is at 82½° E. Local Time there is Indian Standard Time (IST).
- International Date Line passes through Arctic Ocean, Bering Strait, Pacific Ocean, Antarctica, Fiji, Tonga and other islands.
- It is also the longitude where the date changes by exactly one day when it is crossed. If a traveler crossing the date line from east to west, he loses a day and while crossing the date line from west to east, he gains a day.
- Prime Meridian is at 0°. It's called Greenwich line, going through Greenwich near London where the Royal Observatory is.
- Longitudes have an important job: they decide Local Time compared to Greenwich Mean Time (GMT).
- Local Time = noon-sun time in a place.
- Standard Time = Local Time of a country's Standard Meridian.
- India's Standard Meridian is at 82½° E. Local Time there is Indian Standard Time (IST).
International Date Line
- It is an imaginary line drawn at 180° longitude, avoiding the continuous land parts.- International Date Line passes through Arctic Ocean, Bering Strait, Pacific Ocean, Antarctica, Fiji, Tonga and other islands.
- It is also the longitude where the date changes by exactly one day when it is crossed. If a traveler crossing the date line from east to west, he loses a day and while crossing the date line from west to east, he gains a day.