Geography Class 01 to 04

 

Geography Class 01

Geography

• Cosmology includes Galaxies, stars, Sun, and Earth.
• Physical Geography includes  Geomorphology, Climatology, Oceanography, and Biogeography.
• Economic geography includes  Resouces, Agriculture, Industries, and Transportation.
• Social or Human Geography includes the Population, Settlement, and Culture of people.
• An ecological aspect includes Ecosystems, Biomes, Types of vegetation, biodiversity, Pollution, etc.

Syllabus of geography

• Prelims: 
• Indian and World Geography - Physical, Social, Economic Geography of India and the World.
• Mains:
• Salient features of the world’s physical geography.
• Distribution of key natural resources across the world (including South Asia and the Indian sub-continent); factors responsible for the location of primary, secondary, and tertiary sector industries in various parts of the world (including India).
• Important Geophysical phenomena such as earthquakes, tsunamis, Volcanic activity, cyclones, etc., geographical features and their location changes in critical geographical features (including water-bodies and ice-caps) and flora and fauna and the effects of such changes.

PYQ sample discussion 

Sources and reference for geography 

• Have limited sources.
• Primary NCERTs:
• Fundamental of Physical geography.
• India: Physical environment.
• Fundamental of Human geography.
• India people and economy.
• GC-Leong.
• Total geography of 10th class ICSE.
• Class notes(main source).
• VisionIAS value-added material.

Mapping 

• Locations to be remembered:
• Static location.
• Current affair-based location.
• Atlas.

Earth, solar system, and Universe 

• Geography is made up of two words Geo+Graphy which means the description of the earth.
• The term geography was coined by Eratosthenes a greek philosopher called the father of geography.
• Geography is the study of places and relationships between people and their environment.
• The shape of the earth:
• The earth is Flattened at the pole and bulged at the equator.
• It is due to the continuous rotation of the earth.
• This shape is called a geoid or oblate spheroid.
• Neuton proposed this for the 1st time and said the same applies to other planets too.

The topic for the next class: The Shape of the Earth, longitude, and latitude.

Geography Class 02

The shape of the earth 

• The earth is Flattened at the pole and bulged at the equator.
• It is due to the continuous rotation of the earth.
• This shape is called a geoid or oblate spheroid.
• Evidence of the geoid shape of the earth:
• Circumnavigation of the earth- Magellan completed the first circumnavigation in 1519.
• Circular horizon- The horizon appears circular when viewed from a high vantage point and the horizon widens with the increase in altitude.
• Ship's visibility- A ship appears to be rising from water when viewed from the coast or a ship(Bedford level experiment also proves the spherical shape).
• Sunrise and sunset- Different timing of sunrise and sunset at different locations. 
• Eclipse- The earth's circular shadow falls on the moon during a lunar eclipse.
• Other planetary bodies- Since all other planetary bodies are spherical, the earth should also be spherical since the earth is also a part of the same solar system.

Latitude and longitude 

• Latitude:
• Diagramatic representation of latitude:
• 
•  The angular distance of the point on the earth’s surface measured in degrees from the centre of the earth towards north & south of the equator is called the Latitude.
• Parallels of latitudes are the imaginary lines connecting places with the same latitude.
• The largest parallel of latitude is zero degrees and is called the equator.
• The parallels of latitudes are always parallel to the equator and one another.
• The length of the latitude decreases from the equator towards the north pole and south pole, however, the distance between them remains the same.
• The distance between one degree of latitude is equal to 111 km anywhere on the earth.
• Longitude:
• Diagramatic representation of longitude:
• 
• Longitude is the angular distance of a place east or west of the prime meridian.
• Meridians are the semi circles running from pole to pole connecting places with the same longitude.
• The meridians of longitudes are not parallel to each other.
• The distance between them is maximum at the equator and decreases towards the pole.
• The distance between two meridians separated by 1 degree is equal to 111 km at the equator and it gradually decreases and is zero at the pole.
• The length of the meridian always remains the same.
• Great circle:
• It is the longest possible circumference that can be drawn on earth.
• A great circle divides the earth into 2 equal halves.
• An infinite number of great circles can be drawn on the surface of the earth.
• A Great circle is used to find the shortest distance between two locations on the surface of the earth.

The rotation of the earth (7:02 PM)

• The spinning motion of the earth on its axis is called the rotation of the earth.
• The axis of rotation is the imaginary line passing through poles and the centre of the earth around which the earth rotates.
• The orbital plane is the plane in which the earth orbits around the sun.
• The angle between the axis of rotation and the orbital plane is 66.5 degrees.
• The angle of tilt of the axis of rotation from its normal position is equal to 23.5 degrees.
• The direction of rotation is counterclockwise or West to East.
• Period of rotation:
• Solar Day: The time taken by the earth to rotate on its axis so that the sun appears in the same position in the sky is called Solar day.
• The solar day is equal to 24 hours.
• Sidereal day: The time is taken for the earth to rotate on its axis so that a distant star appears in the same position in the sky is called a Sidereal day.
• The sidereal day is equal to 23 hrs 56min.
• Diagramatic representation of solar day Vs sidereal day:
• 
• Speed of earth’s rotation:
• The linear speed of rotation of the earth is the maximum at the equator and reduces towards the poles.
• Therefore rockets are launched closer to the equator so that it provides an initial truth during the launching.

Revolution of the earth (7:43 PM)

• Revolution is the movement of the earth around the sun.
• Earth revolves around the sun in an elliptical orbit.
• The period of the revolution of the earth is 365 days and 6 hrs.
• The average speed of the revolution of the earth is nearly 1 lakh Km/hr.
• The direction of the revolution is in the anti-clockwise direction.
• Perihelion is the position of the earth nearest to the sun (On 3rd January).
• Aphelion is the position of the earth farthest from the sun (On July 4th).

Seasons (7:56 PM)

• Geographical there are 4 seasons- Summer, Winter, Autumn, and Spring.

The topic for the next class: The occurrence of Seasons on earth.

Geography Class 03

Last class revision (5:12 PM)

• Latitude and longitude.
• Rotation and revolution.

Seasons (5:25 PM)

• Tabular presentation for various cases of earth's movement:
•  

Conditions	The angle of incidence(intensity).	Length of the day
Case 1: No rotation. No tilt. No revolution.	90 degrees at the equator(higher intensity). 0 degrees at the poles(lower intensity).	24 hrs of day or night.
Case 2: Rotation is present. No tilt. No revolution.	90 degrees at the equator(higher intensity). 0 degrees at the poles(lower intensity).	12 hrs of the day and 12 hrs of the night across all the latitudes.
Case 3: Rotation is present. Tilt(northern hemisphere towards the sun) is present. No revolution.	90 degrees at 23.5 degrees north. The intensity is higher in the northern hemisphere than in case 2. In the southern hemisphere lower intensity than in case 2.	Equator- 12 hrs of day and night. The length of the day increases toward the northern hemisphere and decreases toward the southern hemisphere.
Case 4: Rotation, tilt, and revolution all are present.	90 Degrees at 23.5 degrees south. The southern hemisphere has a higher intensity than case 2. The northern hemisphere has a lower intensity than case 2.	Equator- 12 hrs of day and night. length of the day increases in the southern hemisphere and decreases in the northern hemisphere.

• Seasons are periods of the year that are characterized by specific climatic conditions.
• There are 4 seasons- Summer, Autumn, Winter, and Spring.
• Seasons are observed on the earth because the earth revolves around the sun with a tilted axis of rotation whose angle of inclination is always constant.
• This causes variations in the intensity of sunlight and length of day throughout the year resulting in seasons
• The regions receiving higher intensity of sunlight for a longer duration experience higher temperatures resulting in summer.
• Those regions receiving lower intensity of sunlight for shorter duration experience winters.
• Diagramatic representation of earth and sun relation:
• 
• Summer solstice:
• It occurs on 21st June.
• The sun's rays fall vertically at the tropics of cancer(23.5 degrees N).
• The intensity of sunlight has increased in the northern hemisphere.
• The length of the day increases from the equator to the north pole.
• Winter solstice:
• It occurs on 22 December.
• Sun rays fall vertically at the tropic of Capricorn(23.5 degrees S).
• The location of the southern hemisphere are receiving higher intensity of sunlight and those in the northern hemisphere lower intensity of sunlight.
• The length of the day decreases from the equator to the north pole.
• Equinox:
• It happens on the 21st of March(Spring Equinox) and the 23rd of September(Autumn Equinox).
• The sun's rays are falling vertically at the equator.
• The length of the day is 12 hrs along all the latitudes.

Video related to seasons (6:31 PM).

The extent of day and night (6:49 PM)

• Position of the overhead sun:
• It is a position where 90-degree sunlight falls.
• The position of the overhead sun is always between 23.5 Degrees N and 23.5 Degrees S.
• Every location between the Tropic of cancer and the Tropic of Capricorn will receive, at least 2 days of 90-degree sunlight and those which are located exactly in the tropics receive 90-degree sunlight only once.
• Polar day:
• It is experienced in regions with 24 hours of daylight.
• The maximum extent of a polar day is 66.5 degrees N and S.
• Polar night:
• It is when there are 24 hours of darkness.

Time Zones (7:20 PM)

• A time zone is a region of the globe that observes uniform standard time.
• The entire globe is divided into 24 time zones with the Greenwich meridian as a standard reference.
• The time along a particular longitude always remains the same.
• From the Greenwich meridian towards the east the time increases(EGA- east gain addition), and towards the west time decreases(WLS-west lose subtraction).
• With a change of every 15 degrees time changes by 60 mins, therefore with a change of every 1 degree, time changes by 4 mins.
• India follows 82.5 degrees east as Indian standard time.
• Multipule time zones:
• India followed 3 time zones based on Bombay, Calcutta, and Madras, along with local Chaibagan time in Assam.
• In 1906 India adopted 82.5 degrees east as Indian standard time(IST) and the local time zones of Bombay and Calcutta were continued till 1955.
• The longitudinal extent of nearly 30 degrees between East and West has resulted in a Mismatch of the Sun cycle and human activities.
• Issues in adopting multiple time zones in India:
• Economic integration- banking, stock exchange, etc.
• Administrative convince- offices, schools, etc.
• Issues in synchronization of transportation- Railways.
• Communication gap impacting security.

The topic of the next class:  International Date Line and Origin of the Universe.

Geography Class 04

Last class revision (5:13 PM)

International date line (5:36 PM)

• Diagramatic representation of international date line:
• 
• It is an imaginary line of demarcation on the earth running from the North to South poles and demarcating the change of calendar day.
• It was agreed in 1884.
• IDL is not a straight line and follows a zig-zag path.
• If a person crosses IDL from West to East, she/he gains a day.
• If a person crosses IDL from East to West, she/he loses a day.

Daylight saving time (5:54 PM)

• It is the practice of shifting time by 1 hour ahead by forwarding the time in the clock just before the beginning of summer.
• It is practised in those regions where the length of the day varies between summers and winters.

Universe (6:05 PM)

• The limitless expanse of space surrounding us consists of the solar systems, stars, galaxies, etc.
• The Universe has around 100-400 billion galaxies with each galaxy having 100-400 billion stars.
• Origin of the Universe:
• Steady-state Theory:
• It was proposed by Fred Hoyle.
• The overall size and mass of the universe remain constant at any point in time.
• The universe has no beginning and no end and is always expanding, creating new stars and galaxies at the rate old ones become unobservable.
• Pulsating Theory:
• Proposed by Arthur Eddington.
• As per the theory Universe expands and contracts alternatively.
• Big Bang Theory:
• It was proposed by Gorgeous Lemaitry in 1927.
• According to the theory, 13.7 billion years ago, the Universe was an extremely compact, dense, and hot singularity.
• There was no matter, no space, and no time.
• 13.7 billion years ago, a cosmic explosion happened called as Bing bang.
• From that time the universe started to expand and is continuing today.
• The expansion subsequently created the forces of Physics including Gravity, the formation of elementary particles, atoms, molecules, gaseous compounds, stars, and galaxies.
• Hubble, in 1929, proposed that all observable stars and galaxies are moving away from earth.
• He discovered this through the phenomenon of the Red Shift.
• The rate of expansion of the universe is called Hubble's constant.

The life cycle of a star (7:16 PM)

• Diagrammatic representation of the life cycle of a star:
• 
• A nebula is a huge cloud of gas and dust mainly consisting of hydrogen.
• The gas is pulled together by gravity and the entire nebula starts to spin.
• The spinning gaseous mass reaches a high temperature resulting in the formation of a hot core called ProtoStar.
• When the temperature of the core crosses 15 million degrees, a nuclear fusion reaction begins at the core resulting in the birth of a star.
• When the supply of hydrogen runs out the core contracts and simultaneously the outer shell expands due to the fusion reaction resulting in Red Giant.
• If it is a low-mass star with less than 10 times the mass of the sun the core collapses leading to the formation of a planetary nebula
• If it is an average star with less than 10 times the mass of the Sun, the core of the Red giant collapses and leads to the formation of a Planetary nebula which is a spherical shell of gas.
• After some time, only the core is left inside the shell, which is called a White dwarf.
• A white dwarf becomes a Black dwarf over some time.
• If the mass of a star is more than 10 times the Sun, the star results in Red Supergiant.
• A Red Supergiant results in a supernova explosion due to the explosion of the iron core
• If the remnant core after the Supernova explosion is between 1.4 to 3 times the mass of the sun, it leads to the formation of a neutron star, which is a very heavy dense body consisting of closely packed neutrons.
• If the remnant core after the supernova explosion is more than 3 times the mass of the sun, the core collapses under gravity leading to the formation of a black hole.
• A black hole is a body with infinite gravity and density that even light can not escape from it.

The topic of the next class: Universe to continue.