- Regional Approach: The regions of the earth are different and these differences must be studied. Descriptive discipline.
- Systemic Approach: Though all places differ in some respects, yet there are similarities between different parts of the world. The aim of the geographer should be to identify these similarities. Analytical discipline.
First geographers: Hecateus and Theophrastus
Kant differentiated between history and geography by proposing that geography is a chorological science while history is a chronological science.
- Physical G: Physical environment and processes of changes on the earth. Consists of geomorphology (similar to geology), climatology, oceanography, biogeography (relationships of organisms with their environment.
- Human G: Study of pattern and activities of human occupancy on earth. Population geography, cultural geography, settlement geography(urban and rural geography), political geography (geopolitics and electoral geography)
- Economic G: Offshoot of human geography. Study of spatial patterns of various economic activities. Consists of agricultural & nutritional geography, industrial geography, transport geography, resource geography, geography of development.
Besides, there can be historical g, military g, radical g, medical g, gender g etc.
Came into existence 4.6 billion years back
Gaseous Hypothesis: (Kant) Clouds of gases flattened down under gravity to create earth.
Nebular Hypothesis: (Laplace) Formed by solidification of a ring thrown away by a rotating nebula (sun)
Tidal Hypothsis: (Jeans and Jeffreys) Proposed effects of two nebulas in forming the earth. A larger nebula came close to the smaller one (sun). The gravitational pull caused tidal upsurge on the surface of sun. As the larger nebula moved away, small rings of nebula separated from the smaller nebula and formed the earth and other planets.
Layered structure: Crust, mantle, core
Crust: sial (silica and aluminium)
Mantle: sima (silica and magnesium)
Outer Core: (nickel and iron)
Age estimated through carbon-dating
Three Eras: Palaeozoic (542 to 241 million years ago), Mesozoic (240 to 64 million years ago) and Cenozoic Era (63 million to 10000 years ago). The era before the Palaeozoic era is called the Pre-cambrian period.
Earlier forms of life have existed as long ago as 3.5 billion years back. Human species came into existence around 2 million years back.
Sun and eight planets
All planets rotate on their axis from west to east except Venus and Uranus which rotate from East to West. Direction of revolution around the sun is also west to east.
Jupiter has the largest number of satellites (63) while Mercury and Venus have none.
Asteroids and planetoids: Bodies revolving around the sun that are small to be classified as planets. Asteroid belt between the orbits of Mars and Jupiter. Jupiter Trojans are asteroids revolving around the sun in Jupiter’s orbit.
Near-earth objects: perihelion distance <1.3 AU.
Geocentric View: Ptolemy; Heliocentric View: Copernicus
Inner planets: Mercury, Venus, Earth and Mars. Rest are outer planets.
Mercury and Venus which are closer to the sun that earth are called inferior planets. Venus is the closest planet to earth.
Most elliptical orbit: Pluto. It intersects with Neptune’s orbit.
Shape: Spheriod. (Oblate spheroid or oblate ellipsoid)
Diameter: Equatorial – 12757 km (7927 miles); Polar – 12715 km (7901 miles)
Geoid: Imaginary shape of the earth where sea level surface of the oceans is extended to the continents to form continuous figure.
Mass: 5.976*1024 kg
Volume: 1.083*1024 liters
Mean density: 5.518 kg/litre
Total Surface Area: 509.7 million sq.km. Land – 148.4 million sq.km (29 pc). Water – 361.3 million sq. Km (71 pc)
Rotation: 23hrs 56 mins 4.09 sec
Revolution: 365 days, 6 hrs, 9 mins and 9.54 sec
Highest point: Mt Everest (8848 m asl)
Lowest point on land: Coast of Dead sea (399 m bsl)
Mean height of land: 756 m
Deepest point: Mariana trench (near Guam: 11033 m bsl)
Avg ocean depth: 3730 m
Earth’s Crust: Oxygen (46.6 pc), silicon (27.7 pc), Al (8.1 pc), Iron (5 pc), Ca (3.6 pc), Na (2.8 pc), K (2.6 pc), Mg ( 2 pc). Other elements (1.6 pc)
Hottest: Lut deserst, Iran (70.7 degreeC)(internet). Al Aiziyah, Libya (58 degree C)
Coldest: Vostok Station, Antarctica (-89.6 degree C)
Inclination on polar axis: 23 deg 26 min 50 sec
Orbital Speed: 29.8 km/s
Mean distance from sun: 149,598,500 km ( 1 AU).
Max distance: 152 million km (aphelion, July 2-5)
Min distance: 147 million km (perihelion, Jan 2-5)
Latitude: Angle subtended by a point to the equatorial place. Lines of latitudes are called parallels.
Longitude: Distance east or west of the meridian of Greenwich.
Equator: Parallel of zero is called equator. It is the largest circle that can be drawn on earth.
Countries on Equator: (countries) Sao Tome and Principe, Gabon, Republic of Congo, Democratic Republic of Congo, Equador, Columbia, Brazil, Uganda, Kenya. Somalia, Indonesia. (water bodies) Atlantic Ocean, Gulf of Guinea, Indian Ocean, Gulf of Tomini, Halmahera Sea, Pacific Ocean.
Geographical Mile: One arc of the equator.
Tropic of Cancer: 23.5 degree North.
Countries on Tropic of Cancer: (countries)Mexico, Bahamas, Western Sahara, Mauritania, Mali, Algeria, Niger, Libya, Egypt, Saudi Arabia, UAE, Oman, India, Bangladesh, Myanmar, China, Vietnam, Taiwan; (water bodies) Red Sea, Arabian Sea, Indian Ocean, Taiwan Strait, Pacific Ocean, Gulf of California, Gulf of Mexico, Atlantic Ocean
Tropic of Capricon: 23.5 degree South
Countries on Tropic of Capricon: (countries) Chile, Argentina, Paraguay, Brasil, Namibia, Botswana, South Africa, Mozambique, Madagascar, Australia; (water bodies) Indian Ocean, Atlantic Ocean, Pacific Ocean
Arctic Circle: 66.5 degree North
Areas on Arctic Circle: (countries) Norway, Sweden, Finland, Russia, US-Alaska, Canada, Greenland, Iceland; (water bodies) Arctic ocean, White Sea, Kandalaksha Gulf, Gulf of Ob, Chukchi Sea, Kotzebue Sound, Norwegian Sea, Davis Strait, Greenland Sea.
Antarctic Circle: 66.5 degree South
Areas on Antarctic Circle: (land) Different regains on Antarctica are claimed by some countries – By this claim the circle passes through territories in Antarctica claimed by Australia, France, Argentina, Chile and United Kingdom; (water) Southern Ocean
The two tropics mark the limit of the zones at between which sun’s rays can be vertical at one time of the other. At tropics, sun rays are vertical once a year while in between the tropics twice a year.
Summer Solistice: Sun overhead Tropic of Cancer
Winter Solistice: Sun overhead Tropic of Capricon.
Greenwich: Prime meridian
Great circle: It is the largest circle that can be drawn on earth. Its plane passes through the centre of the earth. Navigators follow the great circle routes to minimize distance.
Earth’s axis is inclined at 23.5 degree from the line perpendicular to the plane of ecliptic (the plane of orbit of the earth around the sun)
Change of season occurs due to a combined effect of the revolution of the earth around the sun and the inclination of its axis. If the axis was not inclined there would have been no change in the amount of energy received by a place throughout the year and hence no change of season. Also, day and night would have been equal in length.
ritical positions of earth:
Summer solstice: (June 21) Tropic of Cancer receives vertical rays of the sun. North Pole experiences a continuous day while South Pole experiences a continuous night. Longest day in northern hemisphere.
Winter solstice: (December 22)Tropic of capricon receives vertical rays of the sun. South Pole experiences a continuous day while North Pole experiences a continuous night. Longest day in the southern hemisphere.
Exquinoxes: (23rd September and 21st March) Equator receives vertical rays of the sun. Day and night are of equal length throughout the world on these days.
The season in the two hemispheres are reverse of each other
At the equator, the days and nights are exactly equal all the year round. Longer than 24 hours day and night are experienced only in the arctic and Antarctic circles.
Time is reckoned with respect to the position of the sun.
Time of all places on a given meridian is the same.
Time required for one degree rotation is four minutes.
International Date line: The line at 180 degree distance from the prime meridian is called the International Date line. Moving from the west to east one loses a day if he crosses the line. The date in the Eastern Hemisphere is ahead that in the western hemisphere. The date line is bent and altered to keep some countries in the same time zone.
The central meridian for India is the longitude of 82.3 degree E which passes near Allahabad. Indian Standard Time is the time of this meridian. It is 5 hrs 30 minutes ahead of the GMT.
Solar Day: Average time period required for the successive passages of the sun over a given meridian. It is 24 hours
Sidereal day: Time required for a given star in the sky to return to the same position with respect to the earth. It is four minutes less than the solar day. This difference between solar and sidereal day exists because the position of earth with repect to sun keeps changing due to revolution. However, the position with respect a star at infinity is constant.
Solar year: measured with respect to the sun
Sidereal year: measured with respect to a star
Leap year: Since earth takes slightly more than 365 days for revolution around the sun, one day is added every four years to the calendar. This correction is however too large because the actual solar year is 365.2419 days and not 365.25 days. Hence, the leap year is omitted in the century year unless the century year is divisible by 400 (a leap century). Thus, 1900 was not a leap year while 2000 was.
Gregorian Calender: Julius Ceaser. Pope Gregory XII.
Axis of moon makes an angle of 58 degree 43 mins to the ecliptic plane.
Diameter: 3480 km
Mass: 1/81 of earth
Perigee: nearest point to earth (356000 km)
Apogee: Farthest point to earth (407000 km)
Period of revolution around earth: 29.53 days. This is called synodic month.
The time taken by moon to complete one rotation on its axis is exactly same as its sidereal month (27.5 days). Hence, we see the same face of the moon from the earth.
Only 59 percent of the total surface of moon is visible from earth.
Phases: The synodic month begins when the sun and the moon are in conjunction. At this time, moon is dark and called the new moon. This is followed by various phases and the month ends with again the new moon phase.
Tides: Regular rise and fall of water level in the seas and oceans. Twice a day. Successive high tides are about 12.5 hours apart.
Tides are caused by a combined effect of the gravitational pull of moon and sun on earth. When the forces of sun and moon complement each other, higher tides known as spring tides occur. This occurs on full moon and new moon days when the earth, sun and moon are in the same straight line.
When the forces of sun and moon act contrary to each other the tides of lower magnitude known as neap tides occur. Neap tides are observed in the first and the last quarters of the moon.
Tides are stronger at the time of perigee and weaker at the time of apogee.
Tidal range: difference between the water levels at the time of high tide and low tide. It changes from time and place.Narrow bays have higher tidal range.
Bay of Fundy has the highest tidel range in the world.
Tides may lead to advance of water upstream into the rivers. This is known as tidel bore.
Layered structure: troposphere, stratosphere, mesosphere, ionosphere, thermosphere-exosphere
Most important for life forms
Thickness: 8-16 km. (low at poles, high at equator)(more in summer, less in winter)
Contains ¾ of the total molecular mass of the atmosphere.
All weather phenomenon occur here
Temperature: Falls with increasing height at rate of 1 degree for every 165 metres (or 6.5 degree per km). This is called the lapse rate. Lapse rate varies with latitude and altitude. Decreases with altitude. Higher over tropical zone. Hence, the upper limit of troposphere is cooler over the equator than over the poles.
Extends upto height of 50 kms. Upper part is also called ozonosphere.
Uniformity in horizontal distribution of temperature; however, increase with height.
Contains most of atmospheric ozone. Absorbs UV rays.
Free from dust particles and atmospheric turbulence. Ideal for flying aircrafts.
Upto height of 80 km.
Temperature decreases with height.
Mesopause (the upper boundary of mesosphere) is the coldest atmospheric layer with an average temperature of -85 degree C.
Upto 600 km
Contains electrically charged ions. Used for radio communication.
Temperature increases with height.
Most meteors burn up here upon entering the atmosphere.
Thermosphere, Exosphere, Magnetosphere:
Thermosphere: 85-400 km. International Space Station orbits in this layer.
Exosphere: Upto a height of 9600 km. The outermost part of exosphere is called magnetosphere.
There are two belts in the upper atmosphere having a high concentration of ionized particles. They are known as Van Allen’s radiation belts. Lower belt lies at about 2600 km height while the upper belt is about 13000-19000 km height.
Heavier gases concentrated in the lower part while lighter gases are in the upper apart.
Nitrogen (78 pc), Oxygen (21 pc) by volume. They are also called permanent components of the atmosphere.
Proportion of other gases like Co2, H2, water vapour etc varies from place to place. Hence, they are called variable components of the atmosphere.
Nitrogen has a moderating influence on temperature and controls combustion. It is also an important nutrient for vegetative growth.
Oxygen is important for breathing, decomposition and combustion.
Water vapors help in containing temperature.
Carbon dioxide and water vapors lead to greenhouse effect preventing the earth from cooling down excessively.
Ozone: The maximum concentration of ozone is found in the stratosphere, about 25-30 km above the earth’s surface.
Ozone depletion: Ozone depleting at rate of 4 pc per decade since late 70s. Ozone has declined by about 33 pc in the Antarctic. This is known as the Ozone hole.
Global Warming: According to IPCC, global surface temperature increased 0.74 +- 0.18 degree C during the 20th century.
Aurora is natural display of lights in the atmosphere in the polar regions. Produced by the entry of charged particles from the sun into earth’s magnetic field. In northern hemisphere, they are called aurora borealis or northern polar lights. In southern hemisphere, they are called aurora australis or southern polar lights. They are most intense during solar storms.
Magnetic storms are temporary disturbances in the earth’s magnetic field that are supposedly caused by the occurrence of solar flared and sun spots.
Sun spots are temporary phenomena on the surface of the Sun that appear as dark spots compared to surrounding regions. They are caused by intense magnetic activity. They occur in a cycle of 11 years
Insolation is the energy received on the earth surface from the sun.
Although the entire amount of insolation reaching the earth has to pass through the atmosphere, very little of it is absorbed by the atmosphere before reaching the earth’s surface. This is because solar radiation is in the form of short waves for which the atmosphere almost acts as a transparent medium.
When the heated surface of the earth radiates this energy back it is in the form of long waves which is absorbed by the atmosphere.
Distribution of insolation:
Solar constant is the amount of solar energy received upon a unit area of surface held at right angles to the sun’s rays. Its value is 2 gm-calorie/sq.cm/minute. Solar constant, however, varies with sun spots cycle. Also, due to varying sun-earth distance, more energy reaches earth during perihelion than aphelion.
Albedo: The proportion of solar radiation reflected from earth. High for light colored surfaces and low for dark colored ones.
Latitudes affect insolation by affecting the angle of sun’s ray and determining the length of the day. Vertical rays provide more energy.
Slope of land also affects insolation.
So, tropical areas receive the maximum amount of insolation while the polar areas the minimum.
Earth’s temperature remains fairly constant despite insolation because it loses an amount of heat equal to that gained through insolation. This mechanism of maintaining the same temperature is called the heat budget or heat balance.
Long waves in terrestrial radiation.
There are latitudinal variations in heat budget. Tropical areas gain more heat than lost and polar areas lose more heat than gained. This imbalance is corrected by latitudinal transfer of energy. This takes place through air and water circulation.
The process by which radiative energy leaving a planetary surface is absorbed by some atmospheric gases called greenhouse gases.
It is due to this effect that cloudy nights are warmer.
Co2’s greenhouse effect is a factor in global warming.
Temperature at a place, to a large extent, depends on the angle of incidence of sun’s radiation.
Earth receives only about 1/2000 millionth part of the total energy emitted by the sun.
Part of the incident energy is reflected back. Other is absorbed by the surface of earth which gets heated up and starts radiating energy. This makes the air near the earth surface hotter. This fact explains why it is cooler as one goes higher up.
Latitude, altitude, distances from sea, aspect of the land and nature of surface are some of the factors that affect the global distribution of temperature.
Latitude: Highest temperature near the equator and lowest near poles
Altitude: Temp decreases with height
Nature of surface: Albedo. Land has higher albedo than water. However, if the angle of incidence is high and there is movement in water, its albedo might become higher than land.
Distance from sea: Due to difference in specific heats of land and water bodies, land gets heated faster than oceans and cools faster as well. Hence, while oceans have moderate temperatures, continents experience extremes of temperatures. Effect of nearness to sea is called maritime influence while that of location in the interiors of a continent is called continental influence.
Temperature Zones: Torrid zone (tropical region), temperate zone (mid-latitude areas) and frigid zone (polar areas)
Isotherms: The horizontal distribution of temperature is represented with the help of isotherms – the lines joining places with the same temperature. They are generally parallel to the latitudes but are modified at places due to the maritime influence. In the month of July they bend northwards while moving from land to sea while in January they bend southward.
Vertical distribution of temperature: Lapse rate. It is also measured by adiabatic rate. Adiabatic cooling occurs when the air moves upwards and expands. Adiabatic rate higher when air is dry and lower when it is saturated.
When temperature increases with increasing altitude (instead of decreasing), it is called inversion of temperature. Mostly found in mountain valleys.
Air gets cooled and night and becomes heavier to move downwards to the valley and in the process pushing the warmer air upwards. This kind of inversion is also called drainage inversion. It is responsible for frosts at valley bottoms. This is the reason why fruit orchards in mountainous regions are laid on valley slopes instead of valley bottoms.
When inversion occurs due to rapid cooling of air near the surface it is called radiation inversion. It is common in plains in winter.
Advection inversion: When air from a warmer area blows over to a colder surface.
Frontal inversion: When warm air and cold air masses converge, the warm air will rise above the cold air. It is found in latitudes where polar air mixes with tropical air. It leads to foggy conditions.
Thermal anamoly: The difference between the average temperature of a place and the normal temperature of its latitude. They are caused by the factors mentioned before. Depicted on map using isanomals which are lines joining places with equal anomalies. In winter, oceans have postitive anomaly while continents have negative anomaly. Vice versa in summers.
The annual range of temperature is the lowest over the oceans and near the equator.
Thermal Equator: It is the isotherm of the highest mean annual temperature. It is generally taken as coinciding with the geographical equator. The annual range of temperature near the equator is lower than the daily range of temperature.
Pressure = force/area
1 milibar = 1000 dynes/sq.cm.
Measured through barometer. Aneroid barometer: no liquid. Barogram.
Distribution of Pressure:
Pressure is inversely related to temperature and altitude.
Depends on rotation of earth and effect of ascent and descent of air.
There are seven belts of pressure: the equatorial low, the subtropical high (two belts), sub-polar low (two belts) and the polar high (two belts). This is the planetary distribution of pressure.
Swing of pressure belts: Due to the shift in the position of vertical rays of the sun, the pressure belts move slightly northwards during summer solstice and southwards during winter solstice.
Interruption of pressure belts: Due to maritime and continental effects, the pressure belts are not continuous but subdivided into blocks of low and high pressure.
Isobar: lines joining places with equal pressure. Use to show distribution of pressure on map. Sea level affects here as well.
Winds are caused due to differences in pressure.
Pressure gradient: rate of decrease of pressure per unit of horizontal distance. It is measured in the direction of fall of pressure. Direction of the pressure gradient determines the direction of the wind. Its steepness determines the velocity of wind.
Coriollis effect: Deflection of winds due to the rotation of earth. Due to this the winds are deflected to their right in the northern hemisphere and to their left in the southern hemisphere. This is referred to as Farrel’s law.
The May 22, 1960 Valdivia earthquake or Great Chilean Earthquake is to date the most powerful earthquake ever recorded, rating 9.5 on the moment magnitude scale.