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Chapter 11. Universe And Solar System (Geography Notes)


➤ The vast surrounding space is called Universe. It incorporates everything that exists, the stars, planets, satellite as well as our earth and all the objects on it.
➤ Light year and Parsec are the units of measuring distances in the Universe.
➤ One Light year is the distance travelled by light in one year. 1 Light Year = 9.46 × 1012 kilometers.
➤ The nearest star to the earth ‘Alpha Centuari’ is about 4.3 light years away from the earth.
➤ Parsec is an astronomical unit of distance which is equal to 3.26 light years. 1 Parsec = 3.26 light years.
➤ The science dealing with the nature and origin of the Universe is known as Cosmology.
➤ A galaxy is a vast collection of billion of stars, dust and hydrogen gas, isolated in space from similar system.
➤ The two most important galaxies in the Universe are Milky Way Galaxy and Andromeda Galaxy.
➤ Our own Sun and its family of planets belong to the Milky Way Galaxy.
➤ Three basic shapes of galaxies are :
(i) Spiral Galaxy, (ii) Elliptical Galaxy, (iii) Regular Galaxy
➤ Milky Way galaxy is spiral type of galaxy.
➤ Indian name of Milky Way galaxy is ‘Akash Ganga’.
➤ Some of the brightest galaxies are elliptical galaxies.
➤ The stars which appear in the form of closed groups and form recognizable shapes are known as constellations.
➤ The Indian name for constellation is ‘Nakshatras’. About 80 constellations are known.
➤ Some of the important constellations are : Ursa Major : ‘Saptarishi’ Ursa Minor : ‘Laghu Saptarishi’ Orion : ‘Mirga’ Scorpio : ‘Vrischika’ Pleides : Kruttika Cassiopeia : ‘Sarmistha’ Stars
➤ Stars are the heavenly bodies like the Sun that are extremely hot and have light of their own.
➤ Stars are made up of vast clouds of hydrogen gas, helium and dust.
➤ The star which lies immediately above the earth’s North Pole and around which all other stars seem to revolve is called Pole Star.
Life of Stars : Stars pass through a definite evolutionary sequence. The first step in the formation of a star from gases is the Protostar.
(a) A Protostar : It is formed by the gravitational contraction of gases present in the Galaxy. A Protostar is a highly condensed cloud of gases mainly hydrogen and helium.
(b) Red Giants : The continued Nuclear fusion upset the overall equilibrium of the star and to readjust it star’s outer region expands while the core shrinks. Due to the large expansion of the outer shell, the star becomes very big, and its colour changes to red.
(c) Novae and Supernovae : A giant star phase may end in a Novae/ Supernovae stage. These are stars whose brightness increase suddenly by ten to twenty magnitudes or more due to a partial or outright explosion in the star. When brightness increases to 20 magnitudes or more, it is called a Supernovae.
(d) White dwarfs : A Novae/Supernovae explosion in a small star like our Sun (stars lighter than 1.2 solar mass) may leave behind a very dense core of that state. A star of this size cools and contracts to become a White Dwarf.
(e) Neutron star : A supernovae explosion in a star bigger than the Sun but not more than twice as big, may leave behind an extremely dense, residual core of that star, reaching a density of 1014 grams/ cm3, known as Neutron Star.
(f) Pulsar : A spinning neutron star emits radio waves and is called a
(g) Black Holes : A black hole is an object with such a strong gravitational field that even light cannot escape from its surface. Black holes are formed from neutron stars after the Supernoval explosions of big stars. Protostar Red Giants Black Holes Pulsar Neutron Star White dwarf Novae/ Supernovae
Big Bang Theory
➤ The Big Bang Theory formed in 1972, according to this theory every thing in the universe emerged from a point known as singularity, 15 billion years ago.
➤ This theory explains the origin of universe and every thing in it including ourselves on the premise that the universe contained many million of galaxies each one having thousand of millions of stars and each star having numerous planets around them.
➤ The galaxies moved apart from one another as the empty space between them expanded.
➤ In the beginning the universe was much smaller as there was less space between the galaxies.
➤ All the matter in the universe was created in one instant a fixed moment in time.
➤ “As universe expanded for 15 billion years, the hot radiation in the original fireball also expanded with it, and cooled as a result”.
Goldilocks Zone
➤ It is an area of space in which a planet is just the right distance from its home star so that its surface is neither too hot nor too cold. The conditions in the Goldilocks zone are just right so that liquid water remains on the surface of the planet without freezing or evaporating out into space.
Terrestrial planet are more likely to lie in the Goldilocks zone. It is also called as habitable zone or life Zone.
The Solar System
➤ The solar system consists of the Sun, the eight planets and their satellites and various other smaller heavenly bodies such as asteroids, comets and meteors.
The Sun
➤ The sun is a star. It is the star around which the earth and other planets revolve. It is the nearest star to the earth.
➤ Light travelling at a speed of 300,000 km. per second, takes about 8 minutes to reach us from the Sun.
➤ The next nearest star to earth is “Alpha Centuari”.
➤ The Sun is mainly composed of hydrogen. The glowing surface of the Sun which we see is called ‘Photosphere’.
➤ Above the photospheres is the red cloud ‘Chromosphere’. Beyond the chromospheres is the ‘Corona’, which is visible during eclipses.
➤ The temperature of the photospheres is about 6000°C, that of the chromosphere about 32400°C, and that of the corona about 2,700,000°C.
➤ The core of the Sun has a temperature about 15 million degrees C.
➤ The dark lines in the corona are called ‘Fraunhofer lines’. The emission of hydrogen in all directions is called ‘Prominences’.
➤ Sometimes they roll out of the atmosphere to be seen as ‘Solar flares’.
➤ The outward stream of protons flowing out from the corona are called ‘Solar winds’, which is made up of plasma.
➤ The earth’s Magnetosphere or Van Allen belts, as they were earlier called, acts as a shield and deflects the Solar winds.
➤ ‘Sun spots’ are dark patches notched on the surface of the Sun. They appear dark because they are cooler i.e. they have a temperature of about 1500°C.
The Moon
➤ The Moon’s diameter is onefourth of Earth diameter.
➤ Circumference : 11000 km. approximately.
➤ Gravitational Pull in 1/6th of the Earth.
➤ Its orbit around the earth in elliptical orbit.
➤ Distance between the Earth and the Moon is 3,82500 km. approx. (According to NASA)
➤ The distance varies because it revolves around the Earth is an elliptical orbit.
➤ At Perigee the point at which the moon is closest to the Earth, the distance is approximately 3,60000 km.
➤ At Epogee the point at which the moon is farthest to the earth, the distance is approximately 4,05,000 km. (According to NASA).
➤ The Moon is 1/4th size of the Earth.
➤ The Moon take 27 day, 7 hrs, 43 min. and 11.47 sec. to complete one revolution around the Earth.
➤ The Moon in the only satellite of the Earth.
➤ The Moon rotates on its axis in exactly the same time as that of its revolution. That’s why we see only one part of the moon.
➤ We can see only 59% of its surface.
➤ There is no atmosphere on the moon.
➤ The moon has no light of its own. It reflects sun light.
➤ The reflected light by the moon reaches on the Earth in 1.3 seconds.
➤ It has a low albedo (reflection).
➤ It reflects only 7% and the rest is absorbed by venus.
➤ Neil Armstrong and Aldrin reached the moon on 21, July 1969. Through Apollo × 1.
➤ Landing spot is called ‘sea of tranquility’
➤ The black spot on the moon is called ‘sea of tranquility.’
The Earth
➤ It is our planet.
➤ As per order in distance from the sun. It is at third position.
➤ It is at 5th position according to size.
➤ It takes 365 days and 6 hrs. for one rotation around the sun.
➤ It is similiar to venus in shape and size.
➤ It is the only planet where life exists.
➤ It is also called ‘Blue Planet’.
➤ It is the densest of all Planet.
➤ Perihelian is the nearest position of the Earth to the Sun.
➤ The Earth reaches its perihelion on January 3 every year at a distance of about 147 million km.
➤ Aphelian is the farthest position of the Earth from the Sun.
➤ The Earth reaches its aphelian on july 4, when the earth is at a distance of 152 million km.
➤ It is also called ‘Green Planet’ because of ecology.
➤ Venus is the nearest planet to the Earth.
➤ The Earth revolves around the sun at a speed of 29.8 km/second.
➤ An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer.
Solar Eclipse
➤ As observed from the Earth, a solar eclipse occurs when the Moon passes in front of the Sun.
➤ The type of solar eclipse event depends on the distance of the Moon from the Earth during the event.
➤ A total solar eclipse occurs when the Earth intersects the umbra portion of the Moon’s shadow.
➤ When the umbra does not reach the surface of the Earth, the Sun is only partially occulted, resulting in an annular eclipse.
➤ Partial solar eclipses occur when the viewer is inside the penumbra.
➤ When observed at points in space other than from the Earth’s surface, the Sun can be eclipsed by bodies other than the Moon.
➤ Two examples are when the crew of Apollo 12 observed the Earth to eclipse the Sun in 1969 and when the Cassini probe observed Saturn to eclipse the Sun in 2006.
Lunar Eclipse
➤ Lunar eclipses occur when the Moon passes through the Earth’s shadow.
➤ Since this occurs only when the Moon is on the far side of the Earth from the Sun, lunar eclipses only occur when there is a full moon.
➤ There are three types of lunar eclipses : ● Penumbral, when the Moon crosses only the Earth’s penumbra; ● Partial, when the Moon crosses partially into the Earth’s umbra; ● Total, when the Moon crosses entirely into the Earth’s umbra.
➤ Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of the Earth.
➤ Two almost equal high tides and two low tides each day, is called a semi-diurnal tide.
➤ Only one high and one low tide each day, called a diurnal tide.
➤ Two uneven tides a day, or sometimes one high and one low each day; this is called a mixed tide.
➤ The time and amplitude of the tides at a location are influenced by the alignment of the Sun and Moon, by the pattern of tides in the deep ocean, by the amphidromic systems of the oceans, and by the shape of the coastline and near-shore bathymetry.
➤ Tide changes proceed via the following stages : ● Sea level rises over several hours, covering the intertidal zone; flood tide.
● The water rises to its highest level, reaching high tide.
● Sea level falls over several hours, revealing the intertidal zone; ebb tide.
● The water stops falling, reaching low tide, a tides produce oscillating currents known as tidal streams.
➤ The moment that the tidal current ceases is called slack water or slack tide. The tide then reverses direction and is said to be turning.
The Types of Tides : Springs and Neaps
➤ The semi-diurnal range (the difference in height between high and low waters over about half a day) varies in a two-week cycle.
➤ Approximately twice a month, around new moon and full moon when the Sun, Moon and Earth form a line the tidal force due to the sun reinforces that due to the Moon.
➤ The tide’s range is then at its maximum : this is called the spring tide, or just springs.
➤ When the Moon is at first quarter or third quarter, the sun and Moon are separated by 90° when viewed from the Earth, and the solar tidal force partially cancels the Moon’s.
➤ At these points in the lunar cycle, the tide’s range is at its minimum: this is called the neap tide,
➤ Planets are solid heavenly bodies which revolve around the Sun in closed
➤ A Planet is made up of rock and metal.
➤ The Planets move around the Sun from west to east.
➤ There are eight major Planets including earth.
The Eight Planets (Grahas)
(1) Mercury (Budha)
(2) Venus (Shukra)
(3) Earth (Prithvi)
(4) Mars (Mangal)
(5) Jupiter (Brihaspati)
(6) Saturn (Shani)
(7) Uranus (Indra)
(8) Neptune (Varun)
Pluto (Yama) is not a planet now, Pluto is considered as Dwarf planet : Pluto was discovered by Clyde Tombaugh in 1930. The redefinition of planet by the International Astronomical Union (IAU) on August 24, 2006 states that, in the Solar System, a planet is a celestial body that
➤ orbit around the Sun.
➤ has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape.
➤ has cleared the neighbourhood around its orbit.
➤ A non-satellite body fulfilling the first two rule is classified as a Dwarf planet. So, Pluto is considered as Dwarf planet.
➤ A non-satellite body fulfilling the first rule is termed as Small Solar System Body (SSSB).
➤ According to the definition, there are currently eight planets and five Dwarf planets known in the Solar System. The 5 Dwarf planets are Pluto, Ceres, Eris, Makemake and Haumea.
➤ Pluto has been given the number 134340.
Asteroids : Asteroids are very small planets of rock and metal which revolve around the Sun mainly between the orbits of Mars and Jupiter.
Comets : A comet is a collection of gas and dust which appears as a bright ball of light in the sky with a long glowing tail.
Meteors : Meteors are the heavenly bodies from the sky which are seen as a bright streak of light in the sky. The meteors are also called as shooting stars.
Meteorite : A meteor which does not burn completely on entering the earth’s atmosphere and lands on earth surface is known as Meteorite.
➤ Increasing order of planet of distance from the sun.
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
➤ Decreasing order of diameter of planet.
Jupiter Saturn Uranus Neptune Earth Venus Mars Mercury

VenusBrightest Planet, Evening Star, Morning Star, Hottest Planet, Nearest Planet to Earth, Earth’s twin, Slowest rotation in solar system, same period of rotation as revolution, rotates from East to West
EarthBlue Planet, Densest Planet
MarsRed Planet, length of the day is nearly same as that of the Earth
MercurySmallest Planet, Fastest revolution in Solar System, nearest planet to Sun, shortest year, maximum diurnal range of temperature
NeptuneSlowest revolution in Solar System, Coldest Planet
Plutoslowest revolving dwarf planet, coldest and smallest dwarf planet, Biplanet, longest year
Jupiterfastest rotating planet, Biggest Planet
UranusGreen Planet, rotates from North to South
TitanOnly satellite with an atmosphere like Earth
SaturnLeast dense Planet, has maximum number of satellites
Proxima centauriClosest star to the Sun
MarsRed Planet
GannymedeBiggest Satellite
DeimosSmallest satellite

➤ The length of the day is nearly same on the planet Mars as that of the Earth.
Jupiter, Saturn, Uranus and Neptune are the Jovian planets.
➤ The angle of inclination of Mars is nearly same as that of Earth.
Jupiter, Saturn, Uranus and Neptune are the outer planets.
Mercury, Venus, Earth and Mars are inner planets.
Geological Time Scale

Eons Era PeriodEpochYearAge/years Before Present
Cainozoic (From 65 million years to the present times)QuaternaryHolocene Pleistocene0 – 10,000 10,000 – 2 millionModern Man Homo Sapiens
TertiaryPliocene Miocene Oligocene Eocene Palaeocene2 – 5 million 5 – 24 million 24-37 Million 37 – 58 Million 57 – 65 MillionEarly Human Ancestor Ape : Flowering Plants and Treees Anthropoid Ape Rabbits and Hare Small Mannals : Rats – Mice
Mesozoic 65 – 245 Million MammalsCretaceous Jurassic TrjassicNo Epoch65 – 144 Million 144 – 208 Million 208 – 245 MillionExtinction of Dinosaurs Age of Dinosaurs Frogs and turtles
Palaeozolc 245-570 MillionPermian Carboniferous Devonian Silurian Ordovician CambrianNo Epoch245-286 Million 286-360 Million 360-408 Million 408-438 Million 438-505 Million 505-570 MillionReptile dominate-replace amphibians First Reptiles: Vertebrates : Coal beds Amphibians First trace of life on land: plants First Fish No terrestrial Life: Marine Invertebrate
Proterozolc Archean HadeanPre-Cambrian 570 Million 4,800 MillionNo Epoch570-2,500 Million 2,500-3,800 Million 3,800 – 4,800 MillionSoft-bodied arthropods Blue green Algae; Unicellular Bacteria Oceans and Continents form – Ocean and Atmosphere are rich in Carbon dioxide
Origin of Stars Supernova Big Bang5,000-13,700 MillionNo Epoch5,000 Million 12,000 Million 13,700 MillionOrigin of the sun Origin of the universe

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