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  • The solar system is made up of the sun and everything that orbits around it, including planets, moons, asteroids, comets and meteoroids.
  • Sun is the center of the solar system.
  • The sun is by far the largest object in our solar system, containing 99.8 percent of the solar system’s mass.

Fast Fact of Solar System

Age4.568 billion years
Nearest starProxima Centauri (4.22 ly), Alpha Centauri system (4.37 ly)
Nearest known planetary systemAlpha Centauri system (4.37 ly)
Stars1 (Sun)
Planets8 (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune)
dwarf planets5 (Ceres, Pluto*, Haumea, Makemake, Eris)

*In August 2006 the International Astronomical Union (IAU) downgraded the status of Pluto to that of “dwarf planet.” 


Dwarf planet

  • It is a planetary-mass object that is neither a planet nor a natural satellite. It orbits around the sun. There are 5 officially recognised dwarf planets in our solar system, they are Ceres, Pluto, Haumea, Makemake and Eris.
  • Pluto is the most famous dwarf planet. Discovered in 1930, it was long classified as our solar system’s ninth planet.
  • Biggest dwarf planet : Eris
  • Smallest dwarf planet: Ceres

Natural and Artificial Satellites

  • Natural satellites are objects which are formed by nature that orbits another body such as the moon. There are 173 known natural satellites orbiting planets in the Solar System.
  • Artificial satellites are manufactured objects that continuously go round the Earth or some other body in space.
  • The first artificial satellite was Sputnik I.
  • Biggest natural satellite : Ganymede
  • Smallest natural satellite : Deimos
  • The only natural satellite with an atmosphere like earth is Titan.

Asteroids and Planetoids

  • Asteroids are rocky, airless worlds that orbit our sun, but are too small to be called planets and the largest asteroids are called planetoids. e.g. Apophis, Ceres, Pallas, Vesta, Ida, Eros, Gaspra, etc.
  • The near-Earth asteroid is 99942 Apophis. Its diameter is about 325 meters.

Meteors & Meteorites

  • Meteor is a streak of light (a shooting star) that suddenly appears in the sky when a particle from a comet or asteroid enters the Earth’s atmosphere.
  • Meteorite is a fragment of a comet or asteroid that survives its passage through the Earth’s atmoshpeher and lands on the Eart’s surface.
  • 1478 BCE: First recorded observation of meteors.
  • 1908: (Tunguska), 1947 (Sikote Alin), 1969 (Allende and Murchison), 1976 (Jilin) – Important 20th-century meteorite falls.


It is made up of ice, dust and small rocky particles that is a relatively small and it orbits the Sun. e.g. Hale-Bopp, Swift-Tuttle, Hyakutake, Halley, Shoemaker-Levy 9, etc.

Halley’s Comet

It is a “periodic” comet and returns to Earth’s vicinity about every 76 years, making it possible for a human to see it twice in his or her lifetime. The last time it was here was in 1986, and it is projected to return in 2061.

Comet Shoemaker-Levy 9

It was a comet that broke apart and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of Solar System objects. It was first spotted in March 1993 by three veteran comet discoverers: Eugene and Carolyn Shoemaker, and David Levy.



  • Sun formed around 4.57 billion years ago from the collapse of part of a giant molecular cloud that consisted mostly of hydrogen and helium, and probably gave birth to many other stars.
  • The Sun is the center of the Solar System and the source of all life and energy here on Earth. It accounts for more than 99.86% of the mass of the Solar System and it’s gravity dominates all the planets and objects that orbit it.
  • The brightest star of our solar system is sun and its shape is spherical.
  • It is classified as a yellow dwarf star.
  • The Sun rotates from west to east (opposite in direction from that the Earth’s rotation).
  • The interior of the Sun is differentiated between multiple layers, which includes a core, a radiative zone, a convective zone, a photosphere, and an atmosphere. The core is the most dense and hottest region of the Sun (150 g/cm³/15.7 million K) and accounts for about 20–25% of the Sun’s overall radius.

Sunspots are slightly cooler areas on the surface of the sun that appear as dark areas. They only appear dark against the brightness of the rest of the surface of the sun.

Fast Fact of Sun

Spectral Type of StarG2V
Mean diameter1.392684×106 km
Equatorial radius6.96342×105 km
109 × Earth
Mass1.989 × 1030 kg
333,000 × Earth
Surface Temperature (Photosphere)5,500 degree Celcius
Mean distance from Earth1.496×108 km
8 min 19 s at light speed
Rotation Period at Equator26.8 days
Rotation Period at Poles36 days
Composition92.1% hydrogen, 7.8% helium, 0.1% other elements
Luminosity*3.83 × 1033 ergs/sec

* The total energy radiated by the Sun (or any star) per second at all wavelengths


Planets are among the many worlds and smaller objects that orbit the Sun. The formal definition of planet, as voted on by the International Astronomical Union in 2006, is as follows:

A planet is a celestial body that

a)      is in orbit around the Sun,

b)      has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and

c)       has cleared the neighbourhood around its orbit.

There are eight planets in the Solar System, which are in increasing distance from the Sun : Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

In increasing sizes the order is Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars and Mercury.

Classification of Planets

  • The 8 planets are classified into 2 main groups. These are inner planets and outer planets.
  • The Inner Planets (Terrestrial planets) are nearer to the Sun. These are Mercury, Venus, Earth and Mars. They spin slowly.
  • The Outer Planets (Gas giants or Jovian) are further away, larger and made up mostly of gas. These are Jupiter, Saturn, Uranus, and Neptune. They spin quickly.


Earth’s twinVenus
Fastest rotatingJupiter
Slowest rotatingVenus
Closest planet to SunMercury
Farthest planet from SunNeptune
High denseEarth
Low denseMars
Red Planet, Green Planet & Blue PlanetMars, Uranus & Earth



Planet with Symbol


in km

Rotation time

Length of day

Revolution time

Length of year

No. of Satellite(s)

Mercury2,44058d 15h 30m88 days0
Venus6,052116d 18h 0m225 days0
Earth6,37124h 0m365 days and 6 hoursMoon is the

only Satellite

Mars3,3901d 0h 40m1.9 yearsPhobos & Deimos
Jupiter69,9119h 56m11.9 years63
Saturn58,23210h 39m29.5 years62
Uranus25,36217h 14m84.0 years27
Neptune24,62216h 6m164.8 years13 Satellites


  • The Moon (or Luna) is the Earth’s only natural satellite and it is the fifth largest moon in the Solar System.
  • Moonlight is sunlight reflected off of the moon.
  • The rise and fall of the tides on Earth is caused by the Moon.
  • The Moon is moving approximately 3.8 cm away from our planet every year.
  • The Moon has much weaker gravity than Earth, due to its smaller mass, so you would weigh about one sixth (16.5%) of your weight on Earth. This is why the lunar astronauts could leap and bound so high in the air.
  • The Moon has no atmosphere.
  • The first unmanned mission to the Moon was in 1959 by the Soviet Lunar Program with the first manned landing being Apollo 11 in 1969.

Fast facts of Moon

Distance from earth3,82,200 km
Diameter3,475 km
Mass7.3477 × 1022 kg

(0.012300 Earths)

CompositionArgon (Ar), Helium (He), Sodium (Na), Potassium (K), Hydrogen (H), Radon (Rn)
Circumference10,921 km (equatorial)
Apogee  (Farthest distance between earth and moon)405,503 km
Perigee  (Nearest distance between earth and moon)363,295 km
Time taken by Moon light to reach earth1.3 sec
Revolution period around earth27 days, 7 hrs, 43 min, and 11.47 sec.
Rotation period27 days, 7 hrs, 43 min and 11.47 sec.
Highest Mountain35,000 ft (Leibnitz mts)



THE EARTH (Blue Planet)

  • Earth is the third planet from the Sun and is the largest of the terrestrial (inner) planets.
  • It is the fifth largest of the eight planets in the Solar System.
  • It is the only planet in our solar system not to be named after a Greek or Roman deity.
  • It was formed approximately 4.54 billion years ago and is the only known planet to support life.
  • Aphelion (Farthest Distance between earth and sun) : 152,098,232 km
  • Aphelion (Nearest Distance between earth and sun) : 147,098,290 km
  • Apogee (Farthest distance between earth and moon) : 405,503 km
  • Perigee (Nearest distance between earth and moon): 363,295 km
  • The highest point of earth measured from sea level : Mount Everest : 8,848 m (borders Nepal and China)
  • The lowest point of earth measured below sea level : Challenger Deep, at the bottom of the Mariana Trench : 10,911 m

Geographical History of the Earth

Period and Epoch

Beginning Years ago


Cenozoic Era

Quaternary Period

Holocence Epoch

Pleistocene Epoch



2 million


Modern man

Homo Sapiens

Tertiary Period

Pilocene Epoch

Milocene Epoch

Oligocene Epoch

Eocene Epoch

Paleocene Epoch


5 million

24 million

38 million

55 million

63 million


Early human ancestor

Flowering plants and trees

Early horses, cats, dogs, camel

Rabbites, haire

Small mammals: Rats, mice

Mesozoic Era

Cretaceous Period138 millionExtinction of dinosaurs
Jurassic Period205 millionAge of dinosaurs
Triassic Period240 millionFrogs and turtles

Palaeozoic Era

Permian Period290 millionReptile dominate, Replace amphibians
Carboniferous Period330 millionFirst Reptiles and fish
Devonian Period410 millionAmphibians
Silurian Period435 millionCorals
Ordovician Period500 millionGraptolites
Cambrian Period570 millionFirst abundant record of marine life
Pre-cambrian Period4.5 billionFossils extremely rare, consisting of primitive aquatic plants, Evidence of flaciation.  Oldest dated algae, over 2600 million years; Oldest dated meteorite 4500 million years



Age4.54 billion years
ShapeOblate ellipsoid  or  Geoid
Mass5.97 × 1024 kg
Volume1.083 × 1012 km3
Radius6,371 km
Surface area510,072,000 km2
Land area (29.2 %)148,940,000 km2
Water area (70.8 %)361,132,000 km2
Circumference40,075.017 km (equatorial) ; 40,007.86 km (meridional)
Rotation period1 day (23h 56m 4.100s)
Revolution period1 year (365 days, 5 hours, 48 minutes and 45.51 sec)
Time Cordinate of EarthLongitude
Temperature cordinates of EarthLatitude
Average orbital speed29.78 km/s
Composition78.08% nitrogen (N2) (dry air), 20.95% oxygen (O2), 0.93% argon (Ar), 0.039% carbon dioxide (CO2), About 1% water vapor (varies with climate)



Earth’s Rotation

  • The Earth rotates with a speed of 1670 km/h on its own axis from West to East.
  • The axis is an imaginary line passing through the northern and the southern poles.
  • Earth’s rotation is completed in about 24 hours, this is called the daily motion of the earth.
  • This motion is responsible for the occurrence of Day & Night and Rise & fall of tides everyday.

Earth’s Revolution

  • It is the movement of the Earth around the sun in its orbit. Earth’s Revolution speed is 29.8 km/s.
  • This movement of the earth is also from west to east. The period of revolution is one year (365 1/4 days).
  • This motion is responsible for Season and Year.
  • The orbit of the Earth around the sun is elliptical and not circular. Due to this, the distance between the Earth and the sun keeps changing.
  • When this distance is minimum, the Earth is said to be in perihelion (around January 3).
  • When the distance is the maximum, it is said to be in aphelion (around July 4).

Tilt of the Earth’s Axis

  • The tilt of the Earth’s spin axis with respect to the plane of its orbit about the sun (the ecliptic plane) is important for a habitable Earth.
  • The Earth’s spin axis is tilted 23.5° with respect to the ecliptic, giving moderate seasons and preventing temperature extremes anywhere on the planet.
  • When it’s winter in the southern, it’s summer in the northern hemisphere, and vice versa.


  • Equinox is derived from the Latin aequus (equal) and nox (night), because around the equinox, night and day are about equal length.
  • As the Earth moves around its orbit, it reaches two points during the year where the tilt of its axis causes it to be straight relative to the Sun. These days are known as equinoxes.
  • During these equinoxes the rays of the Sun shine directly on the equator.
  • This happens on approximately March 20th and September 22nd.


  • Solstice is derived from the Latin sol (sun) and sistere (to stand still).
  • At two points throughout the year, the tilt of the Earth’s axis reaches its maximum angle compared to the Sun, and begins to move back the other direction.
  • This usually happens around June 21st and December 21st. These days are known as solstices.
  • On these solstices, the rays of the Sun shine directly on one of the two Tropics.
  • During the June Solstice the rays of the Sun shine directly on the Tropic of Cancer.
  • During the December Solstice the Sun’s rays shine on the Tropic of Capricorn.


  • It is a division of the year, marked by changes in weather.
  • Seasons result from the yearly orbit of the Earth around the Sun and the tilt of the Earth’s rotational axis relative to the plane of the orbit.
  • Generally there are four type sof Seasons. These are spring, summer, autumn (fall), and winter.
  • In the Spring, the weather is warmer, and often wetter. Seeds take root and vegetation begins to grow.
  • In the Summer, temperatures may increase to their hottest of the year because Sun is directly overhead the equater. In this season days are long and nights are short.
  • In the Autumn, or fall, temperatures cool again. In northern hemisphere it comes in September and in southern hemisphere it comes in March.
  • In the Winter, temperatures may decreses to their coldest of the year. In this season days are short and nights are long.

Seasons in India

In India, there are six seasons (or Ritu). These are described below

Hindu Season

Gregorian month

Hindu Months

English Names

Vasanta~ March to MayChaitra, VaishakhaSpring
Grishma~ May to JulyJyeshtha, AshadhaSummer
Varsha~ July to SeptemberShraavana, BhadrapadaMonsoon
Sharad~ September to NovemberAshwin, KartikaAutumn
Hemanta~ November to JanuaryMaargashirsha, PaushaWinter
Shishira~ January to MarchMagh, PhalgunaPrevernal


Geographic Coordinate System

  • It is a coordinate system that enables every location on the Earth to be specified by a set of numbers or letters, or symbols.
  • A common choice of coordinates is latitude, longitude and elevation.
  • The invention of a geographic coordinate system is generally credited to Eratosthenes.
  • The webbing of latitude and longitude is known as Graticule.

Latitude (Φ)

  • Latitude (shown as a horizontal line) is the angular distance, in degrees, minutes, and seconds of a point north or south of the Equator. Lines of latitude are often referred to as parallels.
  • Its angular range is 0 to 90° North and South.
  • It denotes distance from north or south (Equator)
  • It is used to classifying temperature zones.
  • Number of horizontal lines (Latitude) is 180.
  • One degree latitude = 111.2 km

Longitude (λ)

  • Longitude (shown as a vertical line) is the angular distance, in degrees, minutes, and seconds, of a point east or west of the Prime (Greenwich) Meridian. Lines of longitude are often referred to as meridians.
  • Its angular range is 0° to 180° East and West.
  • It denotes distance from east or west (Prime Meridian)
  • It is used to classifying time zones.
  • Number of vertical lines (Longitude)is 360.

Time Zones and Universal Time

Universal Time (UT)

  • Time based on the rotation of Earth on its axis with respect to the stars is known as Universal Time.
  • Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory in Greenwich, London.
  • GMT was formerly used as the international civil time standard, now superseded in that function by Coordinated Universal Time (UTC).
  • Coordinated Universal Time (UTC) is the primary time standard by which the world regulates clocks and time. is based on atomic time.

Time Zone

  • Time Zones are a geographical world globe division of 15 degree each, starting at Greenwich, in England.
  • Earth is divided in to 24 longitudinal zones, each being 15 degree or 1 hour apart in time (360/24 = 15 degree in 1 hour) or 1 degree in 4 minutes are called Standard Time Zones.
  • Indian Standard Time (IST) is the time observed throughout India and Sri Lanka, with a time offset of UTC+05:30.
  • Country with largest number of time zones : Russia, 11 time zones
  • Largest country with only one time zone : China

Major world cities and their time zones

Beijing: UTC+8

London (U.K.): UTC

Los Angeles: UTC-8

Melbourne: UTC-10

Mexico City: UTC-6

Moscow: UTC+3

New Delhi: UTC+5.30

New York: UTC-5

Paris: UTC+1

Rome: UTC+1

Sydney: UTC+10

Tokyo: UTC+9

Washington DC: UTC-5

International Date Line (IDL)

  • The International Date Line, established in 1884, passes through the mid-Pacific Ocean and roughly follows a 180 degrees longitude north-south line on the Earth.
  • It is located halfway round the world from the prime meridian – the zero degrees longitude established in Greenwich, England, in 1852.
  • The International Date Line functions as a “line of demarcation” separating two consecutive calendar dates.


An eclipse takes place when one heavenly body such as a moon or planet moves into the shadow of another heavenly body.

There are two types of eclipses are form. Those are : Lunar eclipses and Solar eclipses

Lunar Eclipses

  • The Moon does not have its own light. It shines because its surface reflects the Sun’s rays. A lunar eclipse occurs when the Earth comes between the Sun and the Moon and blocks the Sun’s rays from directly reaching the Moon. Lunar eclipses only happen at full Moon.
  • There are 3 kinds of lunar eclipses: total, partial, and penumbral.
  • A total lunar eclipse occurs when the Earth’s umbra – the central, dark part of its shadow – obscures all of the Moon’s visible surface.
  • A partial lunar eclipse can be observed when only part of the Moon’s visible surface is obscured by the Earth’s umbra.
  • A penumbral lunar eclipse happens when the Moon travels through the faint penumbral portion of the Earth’s shadow.

Solar Eclipses

  • Solar eclipses can only occur during a new Moon, when the Moon moves between the Earth and the Sun and the three celestial bodies form a straight line: Earth – Moon – Sun.
  • There are 3 kinds of solar eclipses: total, partial, annular. There is also a rare hybrid that is a combination of two eclipses.
  • A total solar eclipse occurs when the Moon completely covers the Sun, as seen from Earth. Totality during such an eclipse can only be seen from a very small area on Earth.
  • A partial solar eclipse can be observed when the Earth, Moon and Sun do not align in a perfectly straight line, and the Moon only partially covers the disc of the Sun.
  • An annular solar eclipse occurs when the Moon appears smaller than the Sun as it passes centrally across the solar disk and a bright ring, or annulus, of sunlight remains visible during the eclipse.
  • A hybrid solar eclipse is a rare form of solar eclipse, which changes from an annular to a total solar eclipse along its path.

Planet Transits

When a planet comes between the Earth and the Sun, it is called a transit. The only two planets that can be seen transiting the Sun from Earth are Venus and Mercury, because they are the only planets which orbit inside Earth’s orbit.

From 2000–2099, there will be 14 transits of Mercury. Venus transits are even rarer with only two this century, in 2004 and 2012.


The interior structure of the Earth is layered in spherical shells. It is divied into three parts: crust, mantle and core.

Interior structure

Thickness (km)



Types of rock found

Crust30300-500Silicic rocks, Andesite, basalt at base
Upper mantle720500Peridotite, eclogite, olivine, spinel, garnet, pyroxene, Perovskite, oxides
Lower mantle21713000Magnesium and silicon oxides
Outer core22593000Iron + oxygen, sulfur, nickel alloy
Inner core11215700Iron + oxygen, sulfur, nickel alloy



  • It is the outermost layer.
  • There are two different types of crust: thin oceanic crust that underlies the ocean basins and thicker continental crust that underlies the continents.


  • It the thickest layer of Earth. It comprises about 80% of the Earth’s volume.
  • It has different temperatures at different depths.
  • The steady increase of temperature with depth is known as the geothermal gradient.
  • Rocks in the upper mantle are cool and brittle, while rocks in the lower mantle are hot and soft (but not molten).


  • It is the innermost layer.
  • The core is a layer rich in iron and nickel that is composed of two layers: the inner and outer cores.
  • The inner core is theorized to be solid with a density of about 13 grams per cubic centimeter .
  • The outer core is liquid and has a density of about 11 grams per cubic centimeter.
  • The inner core was discovered in 1936 by Inge Lehmann and is generally believed to be composed primarily of iron and some nickel.

Discontinuety Layers of Earth’s Structure

  1. Connard Layer : It lies between Upper crust and lower crust
  2. Mohorovic Layer : It lies between Crust and mental
  3. Repetti Layer : It lies between Upper mental and lower mental
  4. Gutenberg Layer : It lies between Core and mental
  5. Lehman Layer : It lies between Upper core and lower core

Continental Drift Theory

  • It is the movement of the Earth’s continents relative to each other by appearing to drift across the ocean bed.
  • The theory of continental drift has been replaced by the science of plate tectonics.
  • This theory was proposed by Abraham Ortelius in 1596 and developed by Alfred Wegener in 1912. Wegener was convinced that all of Earth’s continents were once part of an enormous, single landmass called Pangaea.

Seafloor Spreading Theory

  • It is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.
  • It helps explain continental drift in the theory of plate tectonics.
  • It was proposed by Harry Hess in the 1960s. The the phenomenon is known to be caused by convection currents in the plastic, very weak upper mantle, or asthenosphere.

Tectonic Plates

  • The Earth’s lithosphere (the crust and the upper part of the mantle) is cracked into a number of large pieces called tectonic plates.
  • These plates (like big rock rafts) are less dense than the mantle and so float on it and constantly move at relative speeds of a few centimetres per year as a result of convection currents within the Earth’s mantle. The convection currents are driven by heat released by natural radioactive processes in the mantle.
  • Earthquakes, volcanic activity, mountain-building, and oceanic trench formation can occur along these plate boundaries.

There are four types of plate boundaries:

  1. Divergent boundaries – where new crust is generated as the plates pull away from each other.
  2. Convergent boundaries – where crust is destroyed as one plate dives under another.
  3. Transform boundaries – where crust is neither produced nor destroyed as the plates slide horizontally past each other.
  4. Plate boundary zones – broad belts in which boundaries are not well defined and the effects of plate interaction are unclear.

Major Techtonic Plates

Plate name

Area x 106 km2

Pacific Plate103.3
African Plate61.8
North American Plate75.9
Eurasian Plate67.8
Antarctic Plate60.9
Indo-Australian Plate

Indian Plate

Australian Plate




South American Plate43.6



The earth can be affected by two forces which may result into various physical features. These two features are internal and external forces.

The internal forces

These are forces which operate within the earth’s crust. Internal forces include vulcanicity and earth movements, that is, horizontal (lateral) and vertical movements. These forces may result into formation of several landform features.

Vulcanicity (volcanic eruptions)

  • This refers to all the various ways by which molten rock (magma) and gases are forced into the earth’s crust and on to its surface.
  • Vulcanicity therefore includes volcanic eruptions (the formation of volcanoes and lava plateaus and geysers, and the formation of volcanic features such as batholiths, sills and dykes, etc, in the earth’s crust.
  • Active volcano : erupt frequently
  • Dormant volcano : erupted in the recent past but do not erupt frequently.
  • Extinct volcanoes : have not erupted in the historical time and are not likely to erupt.

Types of vulcanicity

There are two types of vulcanicity such as intrusive vulcanicity and extrusive vulcanicity.


Intrusive (internal) vulcanicity

This occurs when the magma cools, solidifies and forms features within the earth’s crust before it reaches the earth’s surface. The features (landforms) formed this way are sometimes termed as intrusive (internal) features.

The landforms formed through intrusive vulcanicity are Dyke, Sill, Laccolith, Lapolith, Batholith and Phacolith.

Extrusive vulcanicity

This is the type of vulcanicity that occurs when molten rocks reach the surface of the earth. When magma emerges at the surface it is called lava. This forms features called extrusive features of vulcanicity.

The landforms formed through extrusive vulcanicity are Acidic lava cone, Basic lava cone, Ash and cinder cone, Crater, Volcanic plug, Composite cone, Caldera, Geysers, hot springs and Lava plateau.