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Solar System

Solar System

The Earth is a planet. It is a member of the solar system. Nine planets and the sun are the main bodies of the ”Solar System”. The planets in the order of increasing distance from the sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Each planet moves around the sun and maintains an elliptical orbit. The orbits of all the planets are almost in the same plane which is close to the equatorial plane of the Sun. The planets also rotate about their axis. About 99.85% of the mass of the solar system is contained within the sun, while the planets collectively make up most of the remaining 0.15 %. On the basis of their location, the planets can be divided into two groups; (i) Inner Planets: Which include Mercury, Venus, Mars, and Earth, (ii) Outer Planets: Which include Jupiter, Saturn, Uranus, Neptune, and Pluto. The planets of the two groups differ markedly in size, density, composition, and rate of rotation.

  • Size: The members of the inner planet group are small in size. On the other hand, the members of the outer planet group are so large that they are often called giants.
  • Density: The inner planets are generally dense, their density being 4×10-3 km-3. or more. The density of outer planets is much lower. For example, Saturn has a density less than that of water.
  • Composition: The lower density of outer planets suggests that they consist mostly of substances like hydrogen, helium, water, ammonia, and methane. The higher density planets consist almost entirely of silicate and metals.
  • Rate of Rotation: The planet Mercury is nearest to the Sun. It has the fastest orbital motion (48 km/sec) and the shortest period of revolution (88 days). Pluto, the most distant planetary body, has an orbital speed of 5 km/sec and requires 248 earth-years to complete on revolution.

Planets in the Solar System

The Solar System comprises of the Sun and eight planets (excluding Pluto) which revolve around it in fixed orbits. The Sun is the center of the Solar system. Distanc-wise Mercury is closest to the Sun followed by Venus, Earth, Mars, Jupiter, Saturn, Neptune. Pluto was excluded from the Solar system by the Scientists and was declared a dwarf planet.

The Sun:
The Sun is a large bright star which forms the center of the Solar System. The speed of 285 km/s and 224 million years to complete one revolution. This period is called cosmic year. The Sun is 400,000 times brighter than the full Moon. At the core of Sun, temperature is about 36 million Fahrenheit (20 million degree Celcius) because the Hydrogen is converted into Helium at the rate of 600 million tons per second. The energy released by these nuclear reactions is in the form of x-rays which heats up the surrounding area extending over millions of miles. The surface temperature of the Sun is about 6000 degree Celsius. It is very large in size with a diameter of 865,400 miles.

The Planets of Solar System:


Mercury is the nearest planet to the Sun. It has a diameter of 4,880 km and revolves in 88 days. The temperature of its surface ranges between -346 degree Fahrenheit on dark side to 950 Fahrenheit on the side facing the Sun. Its surface is highly cratered.


Venus has a diameter of 12,100 km and is the second closest planet to the Sun. It completes a revolution in 224.7 days. Venus has an atmospheric pressure equal to 94.5 times that of Earth. American space craft Magellan reached Venus on 10th August, 1990 and explored its surface. A channel 1.8 km wide, 4,200 miles long was discovered on its surface.


Earth is the third closest planet to the Sun which maintains a distance of 149.6 million kilometer. It has a diameter of 12,756 km and completes a revolution in 365.2 days with a speed of 67 thousand miles per hour. Moreover, it rotates on its axis completing on revolution in 23 hours 56 minutes and 4.09 seconds. Earth has a mass of 6.6 sextillion tons. Atmosphere of Earth comprises of 78 % Nitrogen, 21 % Oxygen, and 1% other gases. The air blanket has a height of 60 miles. The atmosphere of Earth is divided into 5 zones. Troposphere (0-7 miles), Stratosphere (7-30 miles), Mesosphere (30-50 miles), Thermosphere (50-400 miles), Exosphere (above 400 miles). Main data of Earth is as given below.


Mars is the brightest planet in the sky. It is the fourth planet from the Sun with a distance of 227,9 km. It complets one revolution in 687 days. its surface comprises of many craters, volcanoes, chasms and a huge grand canyon. The canyon is 50 miles wide and 2.5 miles deeps and 3000 miles long. The highest elevation is Olympic Mons with a height of 78,000 ft. Mars has two small satellites names Deimos and Phobos. Out of these, Deimos (15 km long) completes a round in 30 30.35 hours whereas Phobos (27 km long) takes 7.6 hours for a revolution. Probing of Mars began in July, 1979 when a space craft Viking I landed on its surface. Later on many other missions provided data about this planet. These included Mars Pathfinder (1996), Mars Global Surveyor (2001), Mars Express (2003), Spirit and Opportunity (2004) and Mars Reconnaissance Orbiter (2005). According to the scientists Mars (Red Planet) is the only planet where chances of life exist due to its similarities with Earth.


It is the fifth closest planet to the Sun with a diameter of 778.3 million km. Jupiter is the largest planet of the Solar with a diameter of 142,000 km. It completes a revolution around the Sun 11.86 years. Its equatorial diameter is 88,786 miles. Jupiter also completes a revolution around its axis in 9 hours and 55 minutes. It is known as giant planet due to its size which is 1,300 times bigger than Earth. Surface of Jupiter has an oval red spot which is equal to the size of Earth. Spacecraft Galileo probed its surface on 7th December, 1995. Jupiter has 63 satellites, out of which the largest are Ganymede (diameter 3,275 miles), Europa (1,950 miles), Calllisto (2,400 miles) and Lo (2,262 miles).

Major Satellites of the Solar System

All the planets of Solar System except Venus and Mercury have satellites (moons). Out of these, Jupiter leads with 63 moons followed by Saturn (56) and Uranus (27). Notable moons of Solar System are as given in the table below.

Planets Total No. of Satellites Major satellites
Mars 2 Phobos, Deimos
Jupiter 63 Europa, Ganymede, Callisto, Sponde, Lo, Amalthea, Isonoe, Megaclite, Aitne, Autnoe, Kalyke.
Saturn 56 Titan, Tethys, Dione, Cassini-Huygens, Mimas, Lapetus, Enceladus, Phoebe, Pan, Dyperion.
Uranus 27 Prospero, Setebos, Sycorax, Puck, Ariel, Stephano, Titania, Umbrial, Oberon, Miranda, Calibon.
Neptune 12 Proteus, Triton, Nereid, Despina, Naiad, Galatea, Larissa.
Satellites of Different Planets of Our Solar System.

What is Universe?

Universe may be defined as the collective name of all the known and unknown celestial objects e.g, the solar system, the stars, the galaxies, constellations, and all the matter which lies in the space between these objects. According to an estimate, the universe is 10-20 thousand million years old and measures 1010 light years across. There are many theories about the origin of universe. Out of these, the Big-Bang Theory says that the universe flashed into existence from a very small agglomeration (mass or collection of things) of matter of extremely high density and temperature. Subsequently, it expanded a dense-hot globule of gas. After 200 million years, the first star came into being. Similarly, the Sun had been formed about 4.5 billion years ago. This process continued for millions of years till all the celestial bodies came into existence.

Theories about the Origin of the Universe

There have, so far, been presented three famous theories about the origin of the Universe.

  1. The Big-Bang Theory
  2. The Oscillating Universe Theory
  3. The Steady-State Theory

(1). The Big-Bang Theory:

According to this theory, the Universe originated as a result of a big explosion that took place about 10-20 thousand million years ago. The matter scattered around and condensed into lumps called galaxies. The Universe has been expanding during all this period. With the passage of time, it has been thinning out. The galaxies are still rushing out. This theory was born of the observation that other galaxies are moving away from our own at great speed in all directions as if they had all been propelled by ancient explosive force. This theory was suggested by a Belgian Priest in the 1020s. He theorized that Universe began from a single primordial atom. The idea was boosted further when Edwin Hubble observed that galaxies are speeding away from us in all directions.

(2). The Oscillating Universe Theory:

According to this theory, the expansion of the Universe will be followed by the contraction of the galaxies resulting in another Big Bang. The process of the Universe continues in an endless cycle of expansion and contraction. Each phase has its own laws of nature.

(3). The Steady-State Theory:

This theory states that the Universe never originated instantly and will continue for ever. With the expansion of the universe, new matter comes into existence and fill the spaces. This theory was put forwarded in 1948 by two Austrian Astrologers, Herman Bondi and Thomas Gold.

Statistics of Universes

  • Sun came into existence about 4.5 million years ago.
  • The Universe is 10-20 thousand million years old.
  • There are thousands of millions of galaxies.
  • Abell is the farthest located galaxy which is about 13,230 million light years away.
  • Diameter of milky way is about 105 light years.
  • The Solar System revolves around the center of Milky Way at a speed of 285 km/s and completes one revolution in 224(106) years.
  • Andromeda Nebule is the closest galaxy to the Milky Way and is 6.8 (105) light years away.
  • A constellation is a group of stars. There are 88 different constellation in the Universe.
  • Sun’s mass comprise of Hydrogen 71%, Helium 21% and other elements 2.5%.
  • Core of the Sun is a huge furnace which has temperature of 36 million degree Fahrenheit. It converts Hydrogen to Helium at a rate of 600 million tons/ second.
  • The Sunspots are patches of gas cooler than gas around them. These occur when lines of magnetic forces break through the Sun’s surface thus preventing some of the heat from reaching that part of the surface of the Sun.
  • Age of Earth is about 4.55 billion years.
  • Jupiter is the largest planet of the Solar system.
  • Venus is the hottest planet of the Solar System.
  • Mercury is the fastest planet of Solar System.
  • Mercury and Venus have no moons.
  • Jupiter has 63 moons, Saturn has 56 moons, Uranus has 27 moons and Neptune has 13 moons.
  • Asteroids are 10,000 small bodies which are circling around the Sun.

Other Celestial Bodies


A galaxy is defined as a huge congregation of stars which are held together by the force of gravity. Galaxies numbering millions lie scattered in the Universe like dots. The galaxies are the clusters of stars. These can be spiral galaxies, elliptical galaxies or irregular galaxies. Out of these, the spiral galaxies are large flattened systems with spiral arms extending outwards from a central nucleus. The Elliptical galaxies have not internal structure and are spherical. The largest ellipticals, exceeds from 1012 solar masses. The irregular galaxies have no particular shape but possess large amount of interstellar matters.

  • Milky Way is a spiral galaxy to which the Sun belongs. It comprises of hundred of thousand million stars. It has a flattened disc which is 120 light years across where as the distance of the Sun from the center is 3,300 light years. Two spiral arms wind out from bulging central nucleus. Black hole exist in the center of Galaxy. A black hole is a region of greatly distorted space, size of which increase with the mass of contracting material. In 2004, the Hubble Space Telescope discovered a new galaxy Abell which is about 13,230 million light years away from the Earth. We belong to galaxy Milky Way, which is a part of a cluster of three dozen galaxies called the local group. The Milky Way is the second largest galaxy of the local group followed by Andromeda Galaxy. The distance from Andromeda galaxy to Milky way is 2 million light years. Apart from Andromeda and Milky way the some of the galaxies of Local Group are:
  • Triangulum Galaxy

The Triangulum Galaxy is a spiral galaxy 2.73 million light-years from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC 598. The Triangulum Galaxy is the third-largest member of the Local Group of galaxies, behind the Milky Way and the Andromeda Galaxy.

  • Large Megellanic Cloud

 It is 158,200 light years distant from the Earth.  Its diameter is 7,000 light years. Its apparent size is (V): 10.75° × 9.17°. The Large Magellanic Cloud is a satellite galaxy of the Milky Way. At a distance of around 50 kiloparsecs, the LMC is the second- or third-closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal and the possible dwarf irregular galaxy known as the Canis Major Overdensity.

  • Messier 32

Messier 32 is a dwarf “early-type” galaxy located about 2.65 million light-years from Earth, appearing in the constellation Andromeda. M32 is a satellite galaxy of the Andromeda Galaxy and was discovered by Guillaume Le Gentil in 1749. M32 measures 6.5 ± 0.2 thousand light-years in diameter at the widest point.Some other features are;

Radius: 3,250 light years

Distance to Earth: 2.489 million light years

Apparent mass: ~3 billion M☉

Magnitude: 8.1

Constellation: Andromeda

Apparent size (V): 8′.7 × 6′.5

  • Small Magellanic Cloud

The Small Magellanic Cloud, or Nubecula Minor, is a dwarf galaxy near the Milky Way. Classified as a dwarf irregular galaxy, the SMC has a diameter of about 7,000 light-years, contains several hundred million stars, and has a total mass of approximately 7 billion solar masses.

Distance to Earth: 199,000 light years

Radius: 3,500 light years

Apparent mass: ~6.5 billion M☉

Distance: 201±6 kly (61.7±2.0 kpc)

Apparent size (V): 5° 20′ × 3° 5′

Coordinates: RA 0h 52m 45s | Dec -72° 49′ 43″

  • Messier 110

Messier 110, or M110, also known as NGC 205, is a dwarf elliptical galaxy that is a satellite of the Andromeda Galaxy.

Distance to Earth: 2.674 million light years

Radius: 8,500 light years

Apparent mass: ~9.3 billion

Magnitude: 8.92

Stars: 10 billion

Apparent size (V): 21′.9 × 11′.0

Leo I

  • Dwarf galaxy

Leo I is a dwarf spheroidal galaxy in the constellation Leo. At about 820,000 light-years distant, it is a member of the Local Group of galaxies and is thought to be one of the most distant satellites of the Milky Way galaxy.

Apparent mass: ~0.02 billion Magnitude: 11.2

Constellation: LeoApparent size (V): 9′.8 × 7′.4

Apparent magnitude (V): 11.2

Distance: 820 ± 70 kly (250 ± 20 kpc)


Constellations are clusters of stars in recognizable patterns visible in the night sky. Major constellations include Big Bear (Ursa Major), Canis Major, Leo, etc. So far, 88 constellations have been discovered.

Constellations and asterisms: what's the difference?
Constellations sky view
  • Andromeda
  • Antila
  • Apus
  • Aquarius
  • Aquila
  • Aura
  • Aries
  • Auriga
  • Bootes
  • Caelum
  • Camelopardalis
  • Cancer
  • Canes Venatici
  • Canis Minor
  • Canis Major
  • Capricomus
  • Carina
  • Cassiopia
  • Centaurus
  • Cephus
  • Cetus
  • Chameleon
  • Circinos
  • Columba
  • Coma Berenices
  • Corona Australis
  • Corona Bonealis
  • Corvus
  • Crater
  • Crux
  • Cygnus
  • Delphinus
  • Dorada
  • Draco
  • Equleus
  • eridanus
  • Formax
  • Gemini
  • Grus
  • Hercules
  • Horologium
  • Hydra
  • Hydrus
  • indus
  • Laeerta
  • Leo
  • Leo Minor
  • Lepus
  • Libra
  • Lupus
  • Lynx
  • Lyra
  • Mensa
  • Microscopium
  • Monceros
  • Musca
  • Norma
  • Octans
  • Ophiuchus
  • Pavo
  • Pegasus
  • Perseus
  • Phoenix
  • Pictor
  • Pisces
  • Piscis
  • Puppis
  • Pyxis
  • Reticulum
  • Sagitta
  • Sagittarius
  • Scorpius
  • Sculptor
  • scutum
  • Serpens
  • Sextans
  • Taurus
  • Telescopium
  • Triangulum
  • triangulum astrale
  • Tucana
  • Ursa Major
  • Ursa Minor
  • Vela
  • Virgo
  • Volans
  • Valpecula
  • Orion


The name comet has been derived from the Greek word Kometes meaning ”Hair Like”. A comet is a large snowball of frozen gases with very little solid matter. it possesses a small nucleus of ice and dust surrounded by bright cloud of gas and dust. there are about 100,000 comets in our solar system. The comets can be classified into short period comets and log period comets. Out of these, the former such as Hailey’s Comet have orbital period of less than 150 years where as the latter have orbital periods of ten thousand years. Some important comets are detailed as under:

(1). Hailey’s Comet:

This comet was discovered by Edmund Hailey in 1682. This comet appears after 76 years period. In 1705, Edmund Hailey said that the comet appearing in the years 1531, 1607, 1682 was the same Hailey’s comet. according to Haiey’s prediction, this comet reappeared in 1758, 1910, 1986.

(2). Comet Smith Tuttle:

This comet was first sighted in 1862 and reappeared in 1992. comet ‘Smith Tuttle is a k kiometer huge ball traveling with a speed of 60 km/s.

(3). Comet Shoemaker Levy-9:

This comet was discovered by scientists Sheomaker, Carolyn andLevy. It is about 10 km long and weighs about 500 billion tons.

A comet can have a nucleus up to 1000 miles in diameter and a tail up to 20 million miles long. On 16th July, 1994, comet Shoemaker was broken into 21 pieces when it crashed in to the surface of Jupiter producing scars on the planet.


A star is gigantic ball of superheated has and keeps hot through nuclear reactions in its center. Sun is also a star in which heat and light is produced through fusion of hydrogen and fission of Helium. It is estimated that the temperature at the core of Sun is 36 million degree Fahrenheit. Thus Star is a luminous body in the sky. Large stars explode a supernovae and the surviving core forms Neutron Stars or Black Hole. Through their gravitational forces, the stars form galaxies by attracting millions of other smaller stars.

Brightest Stars of the Universe

Sr. No Name of Stars Constellations Mag Distance in Light years
1 Serius Canis Major -1.5 8
2 Canopus Carina -0.9 650
3 Alpha Centari Centaurus 0.1 4
4 Vega Lyra 0.1 23
5 Capella Auriga 0.2 42
6 Arcturiss Bootes 0.2 32
7 Rigel Orion 0.3 545
8 Procyon Canis Minor 0.5 10
9 Achemar Eridanus 0.6 70
10 Beta Centauri Centarius 0.9 130
11 Altair Aquita 0.9 18
12 Betelgewse Orion 0.9 600
13 Aldebaran Taurus 1.1 54
14 Spica Virgo 1.2 170
15 Pollux Gemini 1.2 90
16 Antares Scorpions 1.2 170
17 Fomalhunt Piscis 1.3 27
18 Deneb Cygnus 1.3 465
19 Regulus Leo 1.3 70
20 Beta Crucis Crux 1.5 465
21 Eta Carinae Carina 1.7 465
22 Alpha One Crux 1.6 150
23 Castor Gemini 1.6 44
24 Gamma Crucis Crux 1.6 44
25 Epsilon Canis Canis Major 1.6 325
26 Epsilon Ursae ursa Major 1.7 50
27 Bellatrix Orion 1.7 215
28 Lambde Scorpii Scorpion 1.7 325
29 Epsilon Carina Carina 1.7 325
30 Mira Cetus 2.1 250
Famous stars.


A meteor is a small cosmic body which gives a streak of light when it burns up and entering the atmosphere of the Earth. This phenomenon also takes place when the Earth passes through a steam of meteors at the same time each year. An interplanetary rock may have a mass ranging from 10-7 gram to complete asteroid weighing several thousand tons. Due to the long streak of light, the meteor is called a shooting star. The largest meteorite weighing about 70 tons was found at Hoba in Namibia. The fragments of the Meteor fall on Earth creating craters in the surface of Earth.

A meteorite is a piece of cosmic debris weighing over 100 kg that falls on the earth. Thousands of Meteorites fall to the Earth each year. So far, the largest meteorite weighing 70 tons lies embedded near Grootfontein (South West Africa). Similarly another meteorite weighing 34 tons is in exhibition in New York.

Difference among Meteoroid, Meteor and Meteorite:

Meteor: When a small piece of cometary or asteroidal material enters into atmosphere of Earth, it blazes due to friction with atmospheric air and burns down. It is observed in the form of Light streak. It is called Meteor.

Meteoroid: Before entering into Earths’s atmosphere, a cometary material is floating in space near the planet. Now it is called Meteoroid.

Meteorite: Most meteoroids that enter the atmosphere burn up completely as meteors. In some cases, however, the meteoroid does not completely burn up, and the object actually makes it to Earth’s surface. The chunk that has survived its fiery journey and fallen on the surface of Earth is called a meteorite. Or the Unburnt pieces of a Meteor which all on the surface of Earth are called Meteorites.


These are the northern and the southern lights. Out of these, the northen lights are also called Aurora Borealis and the Southern lights are called Aurora Australis. These lights are luminous occurrence in high altitude in various shapes such as arcs, bands and patches. According to modern research, auroras take place due to leakage of electrons from the outer Van Allen layer.


Quasar is a quasi-stellar object which emits tremendous amount of light and microwave radiation. According to an estimate, the quasars emit 100 times as much light as an entire galaxy comprising of millions of stars. The Source of light produced by quasar is the billions of stars which are stuck up in the black holes.


Pulsar is a celestial body which emits radiations at regular interval. It is a rotating Neutron Star which is a star that has gone gravitational collapse and its atoms coalesce into neutrons. The radiation of Pulsar is generated by the electrons moving in the star’s magnetic field.

NASA continues to study pulsars, 50 years after their chance discovery


An eclipse takes place when an astronomical body during its revolution passes through the shadow of another body. The Solar eclipse, and lunar eclipse are its examples. The Solar eclipse takes place when the Moon comes between the Sun and the Earth. As a result, part or full part of the Sun looks black.In the Lunar eclipse, the Earth comes between the Sun and the Moon. Lunar eclipses occur when Earth’s shadow blocks the sun’s light, which otherwise reflects off the moon. There are three types — total, partial and penumbral — with the most dramatic being a total lunar eclipse, in which Earth’s shadow completely covers the moon.

Total Lunar Eclipse - Blood Moon
Lunar Eclips


Moon is a satellite of Earth which revolves around it at a distance 221,463 miles to 252,710 miles. It completes a revolution around the Earth in 27 days and 7 hours. Moon has a diameter of 2,160 miles. Moon is illuminated by the light taken from the Sun. Thus lunar eclipse takes place when The earth comes between Moon and the Sun. The moon revolves around its axis also in 27 days and 7 hours, thus it has only one side which is visible from Earth. It is about 1/4th the size of the Earth. Moon became the first planet to have been visited by man on July 21, 1969, when US astronauts, Neil Armstrong and Edwin Aldrin landed on its surface. Moon has no satellites of its own.


Space is the vast area, which lies between the planets and stars in the Universe. Space is without air and magnetic field. Thus a man becomes weightless in space. The astronauts wear a space suit which helps them survive in space. They travel in specially designed space stations.

Space Stations

The space station is a large spacecraft in which the astronauts remain in space for long period to conduct experiments. Soviet Union became the first country in 1971 to launch a space station named Salyut-I. Two years later, in 1973, USA followed by putting Skylab in the orbit of the Earth.




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