WBBSE Chapter 3 Determination Of Location Of A Place Of The Earth’s Surface Salient Points Introduction
In ancient times, by observing the position of the star in the night sky, the latitude was determined. In the northern hemisphere, latitude can be accurately determined with the help of the Pole Star.
During the daytime, the latitude of a place can be determined by the angle of inclination of the Sun,
In the night sky of the southern hemisphere, latitude can be determined by the angle of inclination of Hadley’s Octant.
Read and Learn Also WBBSE Class 9 Geography And Environment Notes
Latitude is the angular distance of a place either north or south of the Equator on the equatorial plane.
Nowadays, latitudes are determined with the help of Sextant, Transit theodolite, etc. ‘
The lowest and highest values of latitude are 0° and 90° respectively.
Parallels of latitude are the imaginary lines drawn on the maps and globes, that join all the places having the same latitudinal value.
WBBSE Class 9 Determination of Location Notes
Parallels of latitude are extended in an east-west direction. Amongst them, the circumference of the Equator is the largest. Circumference of latitudes decreases with distance from the Equator to the Poles. The total number of parallels at an interval of 1° is 179 to the north and south of the Equator.
Important parallels are the Equator (0°), Tropic of Cancer 23½ºN, Tropic of Capricorn 23½ºS, Arctic Circle 66½ºN and Antarctic Circle 66½ºS.
The distance between the 1° latitudinal interval on the Earth’s surface is about 111 km or 69 miles.
The climate on the Earth’s surface changes with the change of parallels of latitude. Based on climate change, the Earth is divided into 3 heat belts. They are the Torrid zone, the Temperate zone, and the Frigid zone.
Determination Of Location Of A Place Class 9 WBBSE Summary
The angular distance of a place east or west of the Prime Meridian, which is measured in degrees, minutes, and seconds is known as longitude.
The longitude of the Prime Meridian is 0° and the angular distance of other meridians is imagined to the east as well as to the west of the Prime Meridian upto 180°.
Places with the same longitudinal value are joined by semi-circular lines imagined from the North Pole to the South Pole. Such lines are known as Meridians.
The Prime Meridian (0°) and the 180° meridian, which is the exact opposite side of it, together make a full circle, that divides the Earth into two halves. The eastern half is known as the eastern hemisphere and the western half is the western hemisphere.
All the meridians are equal in length, but not parallel to each other. This is because all meridians meet at the Poles.
Understanding Geographic Coordinates for NEET
There is a 4-minute time difference for a 1° longitudinal difference.
Considering the maximum inclination of the Sun on a longitude passing through a place as noon, the time of that place throughout the day is calculated. This specific time of that place is called its local time.
More than one local time is observed in countries with great east-west extension. Therefore, to avoid multiple local times, a meridian is chosen passing through the central position of the country to calculate the standard time of the whole country.
The Indian Standard Time (IST) is calculated based on the meridian (82°30’E) that extends through Mirzapur of Allahabad.
Greenwich Mean Time (GMT) is determined according to the Prime Meridian (0°) passing through Greenwich. The time of the whole Earth is determined as per Greenwich Mean Time.
The time from midnight to noon of the next day is called ante meridian or am. The time from noon to midnight is called post meridian or pm.
Key Terms Related to Location Determination for Class 9
If the center of a circle is drawn on the surface of the Earth and the center of the Earth lies at the same point, then the circle is called the Great Circle.
Parallels of latitude and meridians of longitude intersect each other and form a network, that is called Earth’s grid.
There are two ends of any diameter of the spherical Earth, where one end is the antipode to the other.
A place and its antipode always lie in opposite hemispheres. This is why the difference in longitude and local time between these two places is 180° and 12 hours respectively.
The International Date Line has been imagined through the middle of the Pacific Ocean roughly following the 180° meridian.
The Latitudes and longitudes are measured in degrees(), minutes(‘), and seconds(“). Time is calculated in hours (hrs), minutes (mins), and seconds (secs).
For every 1° longitudinal difference, the time difference is 4 minutes. For every 1′, longitudinal difference, the time difference is 4 seconds.
Concerning the measurement of latitude and longitude: 1°= 60′ and 1′ = 60″.Concerning time calculation: 1h = 60m and 1m = 60s.
GMT refers to Greenwich Mean Time (0° meridian) and IST refers to Indian Standard Time (82½º E meridian).
We move ahead in time as we move from east to west.
While calculating total time, if the time required to deliver a message is mentioned, that time is to be added at the end. On the other hand, while calculating longitude, that extra time is to be subtracted from the total time.
Steps to calculate time based on longitudinal difference—
The first step is to find out the longitudinal difference between the two given places. If both the places are located in the same hemisphere, then the longitude with a smaller value is to be subtracted from the longitude with a larger value. If both the places are located in different hemispheres, then the value of both longitudes is to be added.
The next step is to find out the time difference referring to the fact that, for every 1° longitudinal difference, the time difference is 4 minutes.
The position of the longitude whose time is to be calculated is to be found out concerning the other longitude.
If the place, for which time needs to be determined is to the east, the difference in time is to be added. On the other hand, if the place, for which time needs to be determined, is to the west, the difference in time is to be subtracted.
Steps to calculate longitude based on the time difference—
The first step is to find out the difference in time between the two given places.
The next step is to find out the longitudinal difference by dividing the value of the time difference by 4.
If the time of the place, whose longitude is to be determined, is ahead of that of the other place, then the former is located to the east of the latter. Whereas, if the time of the place, whose longitude is to be determined, is behind that of the other place, then the former is located to the west of the latter.
If the place for which time needs to be determined is in the east, the difference in longitude is to be added and if in the west, the difference in longitude is to be subtracted.
The time difference between a place and its antipode is 12 hours and the longitudinal difference between a place and its antipode is 180°.