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GEOGRAPHY : UNIVERSE & THE SOLAR SYSTEM
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Monday, 03 September 2012 06:49

 


UNIVERSE & THE SOLAR SYSTEM


THEORIES OF ORIGIN

  • Various theories have been proposed to explain the way the Universe was possibly formed. Some such theories are the astronomical phenomenon called the Red Shift or the Doppler Effect, The Big Bang Theory, etc.


DOPPLER EFFECT AND RED SHIFT

  • The shifting of light coming from the galaxies to the red end of the sectrum is known as the Red Shift. The red colour band has the lowest frequency and the longest wavelength in the visible spectrum.

  • This proportionate increase shows that matter in the Universe is in a state of rapid expansion and this idea of rapid expansion is the basis of all the modern theories about the origin of the Universe.

 

BIG BANG THEORY

  • According to the Big Bang Theory, about 10 to 20 billion years ago, cosmic matter (universe) was confined in a super dense ball in a state of extremely high temperature and pressure.

  • A primordial explosion hurled the broken material far into outer space, where the fragmented material is still travelling around at thousands of miles per second.

  • The sudden cooling which accompanied the expansion led to the transformation of atomic particles into atoms of higher elements, which then condensed into gaseous clouds.

  • Eventually, galaxies and other celestial bodies were formed, without disrupting the expansion of the universe.


GALAXIES

  • Galaxy is a huge congregation of millions of stars held together by their own gravitational fields.

  • There are three types of galaxies, as follows:


(i) Spiral Galaxies;


(ii) Elliptical Galaxies; and


(iii) Irregular Galaxies.



LOCAL GROUP

  • A cluster of 23 known galaxies is known as a local group. Milky Way and Andromeda are the two largest known galaxies.


CELESTIAL BODIES MEASUREMENTS UNITS OF SPACE

UNIT

DISTANCE

LIGHT YEAR

It is the distance covered by light in one year in vacuum, at a speed of 3 x 105 km/s This is equal to 5.88 x 106 miles.

Astronomical Units (A.U.)

It is the mean distance between the Earth and the Sun (1.49 x 108 km). One light year is equal to 60,000 A.U.

Parsec

It represents the distance at which the mean radius of the Earth’s orbit subtends an angle of one second of an arc. It is equal to 3.26 light years.

Cosmic/Galactic Year

Sun’s period of revolution around the galactic, which is 250 million years.

  • Distance of the Earth from the Sun = 8 light minutes = 1 A.U.

  • Distance of the Earth from the Moon = 1.25 light seconds.

  • Distance of the Earth from Proxima Centauri = 4.3 light years.


NEBULAE

  • Nebulae are distant stellar systems of luminous bodies (made up of gas and dust particles) e.g. the Orion Nebulae.


CONSTELLATIONS

  • Constellations are clusters of stars, organized into distinct shapes and figures, and named accordingly e.g. Hydra which is the largest constellation.


COMETS

  • Comets are huge clouds of frozen gases and dust which have their home in the cold outer fringes of the solar system.

  • A comet’s head is formed by the evaporation of solid ice particles when the comet approaches the sun.

  • Comets have an extremely eccentric orbit but a definite periodicity, such as the Hailey’s Comet which is seen every 76 years. The tail of a comet always faces away from the sun.

 

METEORS (SHOOTING STARS)

  • Meteors are made up of a small solid matter which, when coming into atmosphere of the earth, burns out due to friction. While burning, they emit light e.g. Leonid shower is a meteor storm (originated in the constellation Leo).


THE WORLD OF STARS

  • Stars account for 98 per cent of the matter in a galaxy. A star is formed by gravitational contraction (from vast clouds of galactic gas and dust).

  • Star-forming matter is richer in hydrogen and helium.


OUR SOLAR SYSTEM

  • The solar system constitutes a collection of heavenly bodies that revolve around the Sun. It includes: (i) The Sun, (ii) The Eight Planets and their satellites, (iii) Asteroids, (iv) Meteors, (v) Comets, and (vi) Drifting particles called inter-planetarydust electrically-charged gases called plasma.


THE SUN

  • One of more than 100 billion stars of the Milky Way.

  • Accounts for 99.85 per cent mass of the solar system.


SOLAR PROFILE

DISTANCE FROM THE EARTH

149.8 million km

DIAMETER

1384000 km

MASS

2 x 1027 tonnes (98.85% of solar system)

SURFACE TEMPERATURE (PHOTOSPHERE)

60000 C

CORE TEMPERATURE

15 million degree

REVOLUTION PERIOD

250 million years

ROTATION TIME

25 days

COMPOSITION

H2 (71 per cent)

He (26.5 per cent)

Others (2.5 per cent)

AGE

5 billion years

EXPECTED LIFE

10 billion years

 

AURORA BOREALIS / AUSTRALIS

  • Aurora Borealis – northern lights (visible in the Arctic region).

  • Aurora Australis – southern lights (visible in the Antarctic region).


PLANETARY WORLD

  • Under the impact of the Sun’s gravitational force, all the eight planets revolve around the Sun, in an elliptical orbit. The planets, in order from the Sun, are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

  • The planets, except Venus and Uranus, rotate anti-clockwise at their axis.

  • The planets on the basis of their characteristics may be classified into: (i) Terrestrial (earth-like) planets or inner planets which have denser material. Planets in this category are Mercury, Venus, Earth and Mars, (ii) Jovian planets (Jupiter-like) or outer planets which are gaseous, gigantic with large satellite families and high rotational velocities. These are Jupiter, Saturn, Uranus, and Neptune
  • The largest terrestrial planet is Earth while the smallest jovian planet is Neptune.

  • The planets in the descending order of their sizes are: Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury.

  • Planets Mercury and Venus have no satellite.

  • Planet closest to the Earth is Venus. After that come Mars, Mercury and Jupiter.


MERCURY

  • Mercury, the innermost planet, has the fastest orbital motion (48 km/s) and the shortest period of revolution, i.e. 88 days.

  • This fast speed keeps it from being drawn into the Sun’s gravitational field.

  • The planet is characterized by the maximum diurnal range of temperature.


VENUS (THE VEILED PLANET)

  • Venus is the closest planet to the Earth. It is also called Earth’s twin because of its similar size, density, and mass.

  • The planet is considered as the hottest planet in the solar system. It has the slowest rotational velocity.



PLANETARY FACTS

PLANET

MEAN DISTANCE

DIAMETER FROM SUN (MILLIONS IN Kms)

PERIOD OF (Kms)

PERIOD OF REVOLUTION ROTATION

AVERAGE DENSITY

Mercury

58

4868

88d

59 d

5.10

Venus

108

12,112

225 d

243 d

5.30

Earth

150

12,742

165.25 d

23 56 d

5.52

Mars

228

6800

687 d

24 37 m

3.94

Jupiter

178

1,43,000

12 yr

9 50 m

1.34

Saturn

1427

1,21,000

29.5 yr

10.25 m

0.70

Uranus

2869

47,000

84 yr

10 45 m

1.55

Neptune

4498

45,000

165 yr

16 7 m

2.27

NOTE: d= days, yr= year, h= hour, m= minutes


EARTH (THE BLUE PLANET)

  • The earth is the fifth largest planet of the solar system. It is the densest planet of the solar sytem.

  • It has such temperature ranges that water can exist here in solid, liquid and gaseous forms. This feature has made possible the existence of life forms on this planet.

 

MARS (THE RED PLANET)

  • The angle of inclination and period of rotation of Mars is nearly the same as that of Earth. Hence Mars has seasons much like the Earth.

  • There is evidence on the surface of Mars of not only stream action, but of catastrophic flooding too. Recently, the European Union’s space missions Beagle-2 and NASA’s Spirit were undertaking for the exploration of Mars.


JUPITER (THE GIANT PLANET)

  • Jupiter is composed mostly of gas and liquid swirling in complex patterns.

  • It has the fastest rotational velocity among planets.

  • Its satellites are, however, solid bodies. The four largest of its sixteen known satellities are: Lo, Europa, Ganemede, and Callisto which are called Galilean satellites. Ganemede is the largest satellite of the solar system.

 

SATRUN (THE RINGED PLANET)

  • Saturn has a spectacular system of seven rings (discovered by Galileo), identified by the letter ‘A’ to ‘G’ (though not in alphabetical order) the rings are made up of individual moonlets of varing sizes.

  • Saturn has the largest number of satellites; a total of eighteen or more. Titan, the largest satellite, is the only one in the solar system with an atmosphere of its own.

 

URANUS (THE GREEN PLANET or THE METHANE PLANET)

  • Its rotational motion has the appearance of rolling, unlike other planets which spin on their axis.

  • Uranus has coldest atmosphere in the solar system.

 

NEPTUNE

  • Uranus and Neptune can be considered twins because of smaller size, colour (pale-greenish), attributable to the methane in their atmospheres.

  • Neptune’s atmosphere contains an earth-sized blemish called the Great Dark Spot.

  • Neptune has eight tiny satellites. Triton is the largest satellite.

 

OUR PLANET: THE EARTH

  • Our earth is a member of the solar family.

  • It has been able to develop and retain an atmosphere, a hydrosphere and, a biosphere, because of its appropriate size and distance from the sun.

 

ORIGIN OF THE EARTH

  • A number of theories have been put forward to explain the origin of the earth and solar system.

  • These theories can be classified into two categories: (i) evolutionary or natural or monistic hypothesis which suppose that the system of planets have evolved from one star or stars; and (ii) the cataclysmic or catastrophic dualistic which believe in some sudden and violent event in space, like the collision or close approach of two stars.

 

SHAPE OF THE EARTH

  • Equatorial diameter – 12,757 km (7,927 miles).

  • Polar diameter – 12,714 km (7,900 miles), less by 43 km (27 miles).

  • The earth is not a perfect sphere. Its shape is like the shape of an orange which is a little flattened on both ends and made to bulge slightly around the centre. The earth too is flattened at the poles and bulges slightly at the equator. This shape is an oblate spheroid. It is also called a ‘geoid’ meaning earth-shaped.

 

MOVEMENT OF THE EARTH

The earth has the following important movements:

(I) ROTATION

  • It is the spinning movement of the earth from west to east on its axis once in 24 hours. The axis is an imaginary line joining the two poles.

  • The phenomenon of day and night is the most important consequence of rotation. The one half of the earth facing the Sun experiences day light, while the other half away from the Sun experiences night.

  • The axis of the earth is tilted at an angle of 23.5o to the vertical. The velocity of the rotation varies, from about 1,700 km per hour at the equator, its half at 60o parallel (850 km/hour) to nearly zero at the poles.

(II) REVOLUTION

  • The movement of the earth around the sun is a fixed elliptical path or orbit. It is called revolution, completed by the earth in 365-1/4 days. This one-fourth day of four consecutive years is added as an extra day on the fourth year as 29thFebruary, making that year a ‘leap year’.

  • Due to the elliptical shapes of the orbit, the earth is closest to the sun on January 3 (at a distance of about 197 million Km) and is said to be at Perihelion.

  • Around July 4 the earth is at farthest from the sun (152 million km away) and is known to be at Apehelion.

  • Average speed of the earth’s revolution is 107,000 km/hour (29.72 km/second).

  • The revolution of the earth coupled with the tilt of the earth’s axis causes the different seasons to occur on the earth.


(III) ECCENTRICITY

  • The shape of the earth’s orbit changes in a cyclic period between 90,000 and 100,000 years. Thus, the orbit of the earth may become more elliptical sometimes, and form a more circular path around the sun at other times.

  • Scholars propose that the Ice Age and Global Warming are effects of such eccentricity of the earth’s orbit.

 

INCLINATION OF THE EARTH’S AXIS

  • The imaginary axis of the earth has a constant angle of inclination of 66-1/2o with the plane of the ecliptic, i.e. the plane in which the earth orbits around the sun.

  • Parallelism is another characteristic of the earth’s axis. As the earth revolves around the sun, the earth’s axis remains parallel to its preceding position.

  • This leads to changes in the altitude of the mid-day sun at different times of the year, in varying lengths of day and night at different times of the year, and in the four seasons.


VARYING LENGTHS OF DAY AND NIGHT

  • Owing to revolution and constant angle of inclination of earth’s axis, the sun is vertically overhead at the tropic of Cancer on 21 June each year.

  • Towards the North Pole, the length of daytime increases, and beyond 66-1/2o N the region has 24 hours light for six months.

  • On 21st June, the Northern Heisphere has its longest day and shortest night. This is known as Summer Solstice.

  • By 22nd December, exactly the same conditions prevail in the Southern Hemisphere when the Sun is vertically overhead at the tropic of Capricorn. This is Winter Solistice, when the Southern Hemisphere experiences its longest day and shortest night.

  • On 21st March and 23rd September, the sun is directly over the equator and all parts of the world have equal days and nights. Hence 21st March and 23rd September are called Vernal and Autumnal Equinoxes respectively.

 

LATITUDE

  • Some important parallels are:

(i)  0o latitude – Equator.

(ii)  23-1/2 o N – Tropic of Cancer.

(iii) 23-1/2 o S – Tropic of Capricorn.

(iv) 66-1/2 o N – Arctic Circle.

(v)  66-1/2 o S – Antarctic Circle.

  • The parallel of 600 is half of the Equator in length and 750 is 1/4th of the Equator.

 

LONGITUDE

  • It is the angular distance measured in degrees along the equator, east or west of the Prime Meridian.

  • The Prime Meridian (00) is that meridian which passes through Greenwich, near London, and from which all other meridians radiate eastwards and westwards upto 180 o.

  • 1o of latitude or longitude represents approximately 111 km. This distance is true for the longitudes along the equator only, since the distance between the longitudes gradually decreases towards the poles to 0 km.

 

LONGITUDE AND TIME

  • Places on the same meridian have the same local (sun) time. Since the earth makes one complete revolution in 24 hours, it passes through 15 degrees in one hour (360 ÷ 24 = 15) or 1o in 4 minutes. The earth rotates from west to east, hence places east of Greenwich see the sun earlier and gain time; whereas places west of Greenwich see the sun later and lose time.

  • A suitable memory acronym is: ‘East –Gain-Add’ (E.G.A.) and ‘West-Lose-Subtract’ (W.L.S.). So, if it is noon in London (near 0o), at a place loacated at 15o E, the time will be one hour ahead of London and the time will be 1 pm. Whereas, at Chennai located on 80o E, the time will be 5 hours 20 minutes ahead of Greenwich. (80 x 4 = 320 ÷ 60 = 5.20 hours) i.e. 5.20 p.m.

  • To avoid confusion of having many local times within one country, usually a country chooses a particular meridian to determine the time for the entire country. This meridian represents the ‘standard time’ followed in that country.

  • Generally, the standard meridians are chosen to differ from the Greenwich meridian by multiples of 15 degrees or seven and a half degrees, i.e. by exact number of hours or half-hours.

  • Thus, the world is divided into a number of time zones.

  • Both U.S.A. and Canada have five time zones each. India has adopted only one time zone, selecting the meridian of 82.5oE for standard time which is 5 hours 30 minutes ahead of G.M.T.

 

EARTH’S SATELLITE : THE MOON

Our moon, the only satellite of the earth, is a fascinating object for the poets as it appears as a beautiful celestial body in the sky. It is a very distinct celestial body in the satellite system, for all other satellites are very small in relation to their mother planets. Whereas, our moon is about ¼ of the size of the earth. Hence moon is referred to by some as a sub-planet. Another interesting fact is that the period it takes for rotation and for revolution are the same (27-1/2 days). As a result, the same lunar hemisphere is always seen from the earth.

  • The moon has no atmosphere as its gravitational power is too weak to hold gases (1/6th of the Earth).

  • The front side of the moon shows (i) the bright parts which are mountains and highlands; and (ii) the darker patches of lowlands which were once thought to be seas and named accordingly as Marias, though the moon has no water at all.

  • The moon has a cratered surface produced by the bombardment of meteors.

  • The different phases of the moon are produced by the changing position of the moon vis-à-vis the sun and the earth.

  • A rare celestial event, the Blue Moon, is said to occur when the second full moon appears within the same month. Still unusual is the occurrence of two blue moons in the same year (as in January and March, 1999).

  • The ocean of tranquillity is the name given to the area where Neil Armstrong and Edwin Aldrin landed on the moon in 1969, to become the first and only humans to set foot on the moon’s surface.

 

LUNAR ECLLIPSE

  • It occurs when the earth comes between the sun and the moon, and the moon is not able to get sunlight due to the shadow of earth cast on it.

  • Lunar eclipse occurs always on full moon, but not on every full moon, since the orbital planes of the earth and moon are cinclined at 5o to each other.

 

SOLAR ECLIPSE

It occurs when the moon comes between the sun and the earth and its shadow is cast on the earth thereby inhibiting the sunlight properly reaching the earth’s surface.

A smaller area in which the moon inhibits all direct sunlight is called the Moon’s Umbra. Here total solar eclipse occurs. In a larger area the sun is covered partially by the moon and the area gets diffused sunlight. This is the Penumbra which experiences partial solar eclipse.

The solar eclipse always occurs on new moon but not on every new moon due to the inclination of the orbital plane of the moon and the earth.

During the final moment of solar eclipse a magnificent flare of sunlight coming through the uneven marginal surface of moon is called the ‘Diamond Ring’.

In a calendar year a maximum of seven eclipses can occur (combining the solare and lunar eclipses). Solar eclipses are more frequent than lunar the ratio being 3:2.

 

INTERNATIONAL DATE LINE

  • A person who travels east of Greenwich gains time till he reaches 180o E where he will be 12 hours ahead of Greenwich and he loses 12 hours when he reaches 180o W. Hence, there is a difference of 24 hours or one day between the two sides of 180o.

  • So, 180o meridian is called the International Date Line which, when crossed, results in change of the date by exactly one day.

  • A traveler crossing this date line from east to west will lose a day, while going from west to east he will gain a day.

  • Thus, when it is midnight on Monday on the Asiatic side, it is Sunday midnight on the American side (as one gains a day going eastward).

To avoid such confusion of day and date in some of the island groups that are cut through by this meridian, the International Date Line has been curved from the normal 180 degree meridian at Berring Strait, Fiji, Tonga, and other islands.

Last Updated on Tuesday, 04 September 2012 02:47
 

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