The big bang theory explains the origin of our universe. According to this theory, 15 billion years ago, cosmic matter was in a compressed state from which expansion started by a primordial explosion. The super-dense ball broke to form galaxies, which again broke to form stars and finally stars broke to form planets including earth.
Since the outer space is limitless, conventional units for measuring distances are not suitable. Hence new units as follows are used:
- Light Year: Distance covered by light in one year in vacuum at a speed of 3×108 m/s. One light year is equal to 9.46 × 1012 kilometers.
- Astronomical Unit: The Mean distance between the Sun and the Earth (1.49 x 108 km). One light year is equal to 60,000 AU.
- Cosmic Year: Sun’s period of revolution around the galactic centre (250 million years). Also called as ‘galactic year’
- Parsec: Distance at which the mean ra- dius of the Earth’s orbit subtends an angle of one second of an arc. It is equal to 3.26 light years.GalaxiesThese are huge congregation of stars that hold together by force of gravity e.g. the Milky Way, Andromeda galaxy, large and small magellanic cloud, Ursa Minor system, sculptor system, etc. Milky Way or Akashganga is our home galaxy. Our solar system is located in this galaxy.
Stars are self luminous bodies that account for 98 percent of the matter in a galaxy. In the universe, some stars appear small but emit more energy than the other stars of the Milky Way. Such stars are called ‘Quasars’. When the dense galactic nucleus is compressing to form a star, this stage in star formation is called a ‘protostar’ stage. Due to high temperature hydrogen converts to
helium and heat and light is emitted. Thus a star is formed. When the hydrogen of a star is depleted, its outer regions swell and redden. This stage of a star is called a ‘Red Giant’. Our sun will turn into a ‘Red Giant’ in 5 billion years. ‘Novae Stars’ are stars whose brightness increases suddenly by 10 to 20 magnitudes due to explosion and then the stars again fade into normal brightness. ‘Super Novae’ are stars whose brightness suddenly increases by more than 20 magnitudes. After the explosion, the dense core of comparatively smaller stars is called the ‘white dwarf’. The dense core of the comparatively larger stars is called the ‘Neutron star’. The neutron star rotates at a high speed emitting radio waves. Such stars are called ‘Pulsar’. ‘Black hole’ stage of the star occurs when the ancient star collapses. Gravity becomes so intense in the hole that nothing escapes, even light.
In the sky at night there are various patterns formed by different groups of stars. These are called constellations. Ursa Major or Big Bear is one such constellation. One of the most easily recognizable constellations is the small bear or Saptarishi (Sapta-seven, Rishi-sages). It is a group of seven stars that forms a part of the large Ursa Major Constellation.
The sun along with its eight planets, asteroids and comets comprise the ‘solar system’. The planets are divided into inner or terrestrial planets which have higher densities e.g. Mercury, Venus, Earth and Mars and outer planets which have lower densities e.g. Jupiter, Saturn, Uranus and Neptune.
• • •
The sun is in the center of the solar system.
It is made up of extremely hot gases par- ticularly hydrogen.
The sun is 109 times bigger than the earth and weighs 2 × 1027 tonnes.
- The sun is about 150 million km away from the earth. The light from the sunreaches earth in about 8 minutes.
- The glowing surface of the sun is called ‘Photosphere’. Above the ‘Photosphere’ is red coloured ‘Chromosphere’. Beyond the Chromosphere is the ‘Corona’, visible during eclipses.
- The temperature of the photosphere isabout 6000°C and that of the Chromo- sphere is 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 Kelvin. But that tremen- dous heat is not felt so much by us be- cause despite being our nearest star, it is far away from us.
- It takes 250 million years to complete one revolution round its centre. This period is called ‘Cosmic year’.
- 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 ‘Aurora Borealis’ or northern lights are multicoloured lights that sweep across the sky in waves and are visible in the arctic region. The ‘Aurora Aus- tralis’ or southern lights are similarly visible near the Antarctica region.The Moon
- The moon is the only satellite of the earth.
- Its size is approximately one-fourth that of the earth. It has a diameter of 3475 km.
- Its orbit is elliptical. The maximum dis-tance (apogee) of the moon from the earth is 406,000 km and the minimum distance (perigee) is 364,000 km.
- The moon moves around the earth in about 27 days. It takes exactly the same time to complete one spin. As a result, only one side of the moon is visible to us on the earth.
- The bright parts of the moon are moun- tains whereas the dark patches are low- lying plains.Asteroids
45,000. ‘Ceres’ whose length is about 1000km is the largest one. They revolve around the sun in the same way as the planets.
Meteors and Meteorites
The meteors are the remains of comets which are scattered in the interplanetary space of the solar system. On contact with the earth’s atmosphere, they burn due to friction. Those which completely burn out into ash are called meteors or ‘shooting star.’ Those which do not burn completely and strike the earth in the form of rocks are called ‘meteorites’.
There are eight planets in our solar system. They are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Earlier, Pluto was considered as a planet. But recently it has lost this status. All the eight planets of the solar system move around the sun in fixed paths. These paths are elongated. They are called orbits. A new planet 2003 UB 313 has been discovered recently in our solar system. It is bigger than Pluto and farthest from the Sun.
- Mercury is the smallest and the nearest planet to the Sun.
- It takes only about 88 days to complete one round along its orbit.
- It has no atmosphere and no satellite.
- Its days are scorching hot and nights are frigid.
It is also called the ‘morning’ or ‘evening star’.
It is probably the hottest planet because its atmosphere contains 90-95% of carbon dioxide. The day and night temperatures are almost the same.
The atmospheric pressure is 100 times that of the earth.
It has no satellite.
Asteroids are a series of very small planets or fragments of planets lying between the orbit of Mars and that of Jupiter. They number about
C. The Earth
- The earth is the third nearest planet to the Sun.
- In size, it is the fifth largest planet.
- It is slightly flattened at the poles. That is why its shape is described as a Geoid.
- From the outer space, the earth appears blue because its two-thirds surface is covered by water. It is, therefore, called a blue planet.
- It is marked with dormant volcanoes and deep chasms where once water flowed.
- It has a thin atmosphere comprising of Nitrogen and Argon.
- Beneath its atmosphere, Mars is barren, covered with pink soil and boulder. Because of this it is known as ‘red planet’.
- It has two satellites namely ‘Phobos’ and ‘Demos’.
- The highest mountain here is Nix Olympia which is three times higher than Mount Everest.
- Recent explorations have thrown light on the possibility of existence of life here.
- It is the largest planet of the solar system.
- Its atmosphere contains hydrogen, helium, methane and ammonia.
- It contains two and a half times the mass of all the other planets combined.
- It reflects more than three times the energy it receives from the sun.
- It has the great red spot which is an enormous eddy in the turbulent cloud cover. It also contains dusty rings and volcanoes.
- It has 16 satellites like Ganymede, Aayo, Europa, Callisto etc.
270,000 km in diameter.
- It has 21 known satellites. Among them Titan, Phobe, Tethys and Mimas are important.
- Its moon, Titan has nitrogen atmosphere and hydrocarbons, the necessity of life but no life exists.
- It is the only planet that lies on its side. Hence, one pole or the other faces the sun as it orbits.
- It is one of the coldest planets because of having an average temperature of -223?C.
- Its atmosphere is made of mainly hydrogen. The landscape is barren and there is frozen methane cloud.
- There are 9 dark compact rings around the planet and a corkscrew shaped magnetic field.
- It has 15 satellites; prominent ones are Aerial, Ambrial, Titania, Miranda etc.
- It rotates north to south.
- It is the most distant planet from the sun.
- There are five rings of Neptune. The outer ring seems to be studded with icy moonlets while the inner ring appears narrow and nearly solid.
- It has 8 satellites like Titron, Merid, N-1, N-2, N-3 etc.
- Its atmosphere mostly contains hydrocarbon compounds. The atmosphere appear blue, with quickly changing white icy methane clouds often suspended high above an apparent surface.
Pluto from Planet to Plutoid
Pluto, demoted from planet status in 2006, got a consolation prize – it and other dwarf planets like it will be called plutoids. Plutoids are celestial bodies in orbit around the Sun at a distance greater than that of Neptune that have sufficient mass for their hydrostatic equilibrium (near- spherical) shape. The two known plutoids are Pluto and Eris. It is expected that more plutoids will be named as science progresses and new discoveries are made.
It is the second largest planet of the solar system.
It has a celebrated rings composed of thousands of rippling, spiraling bands of icy rock and dust just 200 feet thick and Motions of the Earth
The earth has two main motions: (i) Rotation and (ii) Revolution.
The axis of the earth, which is an imaginary line, makes an angle of 661⁄2° with its orbital plane.
The plane formed by the orbit is known as the orbital plane. The earth receives light from the sun. Due to the spherical shape of the earth, only half of it gets light from the sun at a time. The portion facing the sun experiences day while the other half away from the sun experiences night. The circle that divides the day from night on the globe is called the circle of illumination. This circle does not coincide with the axis as you see in the given figure.
Rotation: The earth rotates around its axis. The axis is an imaginary line passing through the centre of the earth. The earth completes one rotation in 23 hours, 56 minutes, 4.09 seconds to be exact. The earth rotates from west to east. The period of rotation is known as the earthday.
Effects of the Rotation of the Earth
(i) Causation of day and night
(ii) A difference of 1 hour between two meridians which are 15°apart.
(iii) Deflection of ocean currents and winds. (iv) Rise and fall of tides every day
Revolution: It is earth’s motion in its elliptical orbit around the sun. One revolution is completed in 365 1/4 days, resulting in one extra day every fourth year. The year, consisting of 366 days is called a “leap year” having 29 days in the month of February.
A year is usually divided into summer, winter, spring and autumn seasons. Seasons change due to the change in the position of the earth around the sun.
On 21st June, the Northern Hemisphere is tilted towards the sun. The rays of the sun fall directly on the Tropic of Cancer. As a result, these areas receive more heat. The areas near the poles receive less heat as the rays of the sun are slanting. The North Pole is inclined towards the sun and the places beyond the Arctic Circle experience continuous daylight for about six months. Since a large portion of the Northern Hemisphere is getting light from the sun, it is summer in the regions north of the equator. The longest day and the shortest night at these places occur on 21st June. At this time in the Southern Hemisphere all these conditions are reversed. It is winter season there. The nights are longer than the days. This position of the earth is called the Summer Solstice.
On 22nd December, the Tropic of Capricorn receives direct rays of the sun as the South Pole tilts towards it. As the sun’s rays fall vertically at the Tropic of Capricorn (231⁄2° S), a larger portion of the Southern Hemisphere gets light. Therefore,
it is summer in the Southern Hemisphere with longer days and shorter nights. The reverse happens in the Northern Hemisphere. This position of the earth is called the Winter Solstice.
On 21st March and September 23rd, direct rays of the sun fall on the equator. At this position, neither of the poles is tilted towards the sun; so, the whole earth experiences equal days and equal nights. This is called an equinox.
On 23rd September, it is autumn season in the Northern Hemisphere and spring season in the Southern Hemisphere. The opposite is the case on 21st March, when it is spring in the Northern Hemisphere and autumn in the Southern Hemisphere. Thus, we find that there are days and nights and changes in the seasons because of the rotation and revolution of the earth respectively.
Some terminologies related to revolution are:
• Perihelion: The position of the earth when it is at its nearest point to the sun. The earth reaches its perihelion on about 3rd January at a distance of about 147 million km from the sun.
• Aphelion: The position of the earth when it is at its greatest distance from the sun. The earth reaches its aphelion on 4th July when it is at a distance of 152 million km from the sun.
- Perigee: The point in the orbit of the moon when it is nearest to the earth.
- Apogee: The point in the orbit of the moon when it is farthest from the earth.Effects of the Revolution of the Earth
- (i) Change of seasons.
- (ii) Variation in the lengths of day and night at different times of the year.
- (iii) Shifting of wind belts.
- (iv) Determination of latitudes.Lattitude and Longitude
Latitude of a place on the earth is the angular distance of the place from the equator. 1° of latitude is approximately equal to 111 km.
Parallels of Latitude: They are circles drawn on the globe parallel to the equator. All the places on a parallel of latitude will have the same latitudinal angle.
Important Parallels of Latitude
Tropic of Cancer Tropic of Capricorn Arctic circle
23 1⁄2°N 231⁄2°S 661⁄2°N 661⁄2°S
Heat Zones of the Earth
The mid-day sun is exactly overhead at least once a year on all latitudes in between the Tropic of Cancer and the Tropic of Capricorn. This area, therefore, receives the maximum heat and is called the Torrid Zone.
The mid-day sun never shines overhead on any latitude beyond the Tropic of Cancer and the Tropic of Capricorn. The angle of the sun’s rays goes on decreasing towards the poles. As such, the areas bounded by the Tropic of Cancer and the Arctic Circle in the Northern Hemisphere, and the Tropic of Capricorn and the Antarctic Circle in the Southern Hemisphere, have moderate temperatures. These are, therefore, called Temperate Zones.
Areas lying between the Arctic Circle and the North Pole in the Northern Hemisphere and the Antarctic Circle and the South Pole in the Southern Hemisphere, are very cold. It is because here the sun does not rise much above the horizon. Therefore, its rays are always slanting. These are, therefore, called Frigid Zones.
Great Circles: Any circle which divides a globe into hemispheres is a great circle. The equator is a great circle and Greenwich meridian together with meridian 180° make another great circle. The number of great circle is limitless. Great circle can extend in any direction: east to west, north to south, north east to south west, and so on. Great circles are of equal length.
The longitude shows the distance of a point east or west of the Prime Meridian which is at 0° and passes through Greenwich, near London. For each degree of longitude there is a difference of four minutes in time.
Longitude and Time: The best means of measuring time is by the movement of the earth and the moon. The sun regularly rises and sets every day, and naturally, it is the best time-keeper throughout the world.
When the Prime Meridian has the sun at the highest point in the sky, all the places along this meridian will have mid-day or noon. As the earth rotates from west to east, those places east of Greenwich will be ahead of Greenwich time and those to the west will be behind it. The rate of difference can be calculated as follows. The earth rotates 360° in about 24 hours, which means 15° an hour or 1° in four minutes. Thus, when it is 12 noon at Greenwich, the time at 15° east of Greenwich will be 15 × 4 = 60 minutes, i.e., 1 hour ahead of Greenwich time, which means 1 p.m. But at 15° west of Greenwich, the time will be behind Greenwich time by one hour, i.e., it will be 11.00 a.m. Similarly, at 180°, it will be midnight when it is 12 noon at Greenwich.
Greenwich Mean Time: The local time at Greenwich or any place on the Prime Meridian. All meridians to the east of Greenwich meridian have sunrise before that meridian. Local times along these meridians are therefore ahead of G.M.T. Meridians to the west of Greenwich meridian have sunrise after this meridian and therefore their local times are behind G.M.T.
Standard Time: A particular meridian of longitude passing through a country is chosen as the reference meridian. The local time along this meridian, calculated with respect to Greenwich Mean Time in terms of its longitude is taken as the Standard Time for that country.
Why do we have standard time?
The local times of places which are on different meridians are bound to differ. For example, it will be difficult to prepare a time-table for trains which cross several longitudes. In India, for instance, there will be a difference of about 1 hour and 45 minutes in the local times of Dwarka in Gujarat and Dibrugarh in Assam. It is, therefore, necessary to adopt the local time of some central meridian of a country as the standard time for the country.
Indian Standard Time: Time along 82 1⁄2° E meridians, calculated with respect to G.M.T. India, for being a large country, is unusual in having a single time zone all over the country. It is 51⁄2 hours ahead of G.M.T.
International Date Line: An imaginary zigzag line on the globe, approximately along the 180° meridian of longitude. When a person crosses this line from East to West, he gains one day and when he crosses from West to East, he loses one day.
Solar Day: It is the time interval between successive crossings of the sun across the meridian of the celestial sphere of any fixed place in the same direction. This is equal to 24 hours.
Sidereal Day: The period of rotation of the earth about its axis. This is calculated with respect to any fixed star. It is 4 minutes less than 24 hours.
Solar Year (Tropical year): It is the average interval between successive returns of the sun in its apparent motion along the ecliptic to a fixed position on the celestial sphere of any fixed place. This is equal to 365.24 mean solar days.
Sidereal Year: The period of revolution of the earth around the sun. It is calculated with reference to any fixed star. It is approximately equal to 365.26 days.
To account for 1/4 of a day in a year, the leap year system is adopted in the Gregorian calendar. To account for the excess of 11 minutes in a year, the centurial year is considered a leap year only when it is divisible by 400.
Mean density Total Surface Area Land Area
Greatest Ocean Depth
Mean Equatorial Diameter
4,550 million years 5.976 × 1024 kg. 5.518 kg/litres. 510,000,000 km2. 29.2% of the total surface area. 70.8% of the total surface area.
11,033 m (Mariana Trench)
Earth in Figures
11. Equatorial circumference 40,076 km.
Theories of Origin of Earth
- Buffon-Hypothesis: Based on sun-comet collision.
- Kant-Gaseous Mass Theory: Based on Newton’s law of gravitation.
- Chamberlain-Moulton: Planetesimal Hypothesis.
- Jeans & Jeffery: Tidal Hypothesis: Based on sun-giant star attraction.
- Alfven: Electromagnetic Hypothesis.
- Russell and Littleton: Binary StarHypothesis.
- Ross-Gun-Fission Hypothesis: Rotational and Tidal hypothesis.
- F . Hoyle: Super Nova Hypothesis.
- Big Bang Theory: Latest idea.Major domains of the earthEarth is the only planet which has life.
Human beings can live here because the life sustaining elements of land, water and air are present on the earth. The surface of the earth is a complex zone in which three main components of the environment meet, overlap and interact. The solid portion of the earth on which we live is called the lithosphere. The gaseous layers that surround the earth, is the atmosphere, where oxygen, nitrogen, carbon dioxide and other gases are found. Water covers a very big area of the earth’s surface and this area is called the hydrosphere. The hydrosphere comprises water in all its forms, that is, ice, water and water vapour. The biosphere is the narrow zone where we find land, water and air together, which contains all forms of life.
The solid portion of the earth is called the lithosphere. It comprises the rocks of the earth’s crust and the thin layers of soil that contain nutrient elements which sustain organisms. There are two main divisions of the earth’s surface. The large landmasses are known as the continents and the huge water bodies are called the ocean basins. All the oceans of the world are connected with one another. The level of seawater remains
the same everywhere. Elevation of land is measured from the level of the sea, which is taken as zero.
The highest mountain peak Mt. Everest is 8,848 metres above the sea level. The greatest depth of 11,022 metres is recorded at Mariana Trench in the Pacific Ocean.
There are seven major continents. These are separated by large water bodies. These continents are – Asia, Europe, Africa, North America, South America, Australia and Antarctica.
Asia is the largest continent. It covers about one-third of the total land area of the earth. The continent lies in the Eastern Hemisphere. The Tropic of Cancer passes through this continent. Asia is separated from Europe by the Ural Mountains on the west. The combined landmass of Europe and Asia is called the Eurasia (Europe + Asia).
Europe is much smaller than Asia. The continent lies to the west of Asia. The Arctic Circle passes through it. It is bound by water bodies on three sides.
Africa is the second largest continent after Asia. The Equator or 0° latitude runs almost through the middle of the continent. A large part of Africa lies in the Northern Hemisphere. It is the only continent through which the Tropic of Cancer, the Equator and the Tropic of Capricorn pass. The Sahara Desert, the world’s largest hot desert, is located in Africa. The continent is bound on all sides by oceans and seas. The world’s longest river, the Nile, flows through Africa.
North America is the third largest continent of the world. It is linked to South America by a very narrow strip of land called the Isthmus of Panama. The continent lies completely in the Northern and Western Hemisphere. Three oceans surround this continent.
South America lies mostly in the Southern Hemisphere. The Andes, world’s longest mountain range, runs through its length from north to south. South America has the world’s largest river, the Amazon.
Australia is the smallest continent that lies entirely in the Southern Hemisphere. It is surrounded on all sides by the oceans and seas. It is called an island continent.
Antarctica, completely in the Southern Hemisphere, is a huge continent. It is larger than the combined area of Europe and Australia. The South Pole lies almost at the centre of this continent. As it is located in the South Polar Region, it is permanently covered with thick ice sheets. There are no permanent human settlements. Many countries have research stations in Antarctica. India also has research stations there. These are named as Maitri and Dakshin Gangotri.
The earth is called the blue planet. More than 71 per cent of the earth is covered with water and 29 per cent is with land. Hydrosphere consists of water in all its forms. As running water in oceans and rivers and in lakes, ice in glaciers, underground water and the water vapour in atmosphere, all comprise the hydrosphere. More than 97% of the Earth’s water is found in the oceans and is too salty for human use. A large proportion of the rest of the water is in the form of ice-sheets and glaciers or under the ground and a very small percentage is available as fresh water for human use.
Oceans are the major part of hydrosphere. They are all interconnected. The ocean waters are always moving. The three chief movements of ocean waters are the waves, the tides and the ocean currents. The four major oceans are the Pacific Ocean, the Atlantic Ocean, the Indian Ocean and the Arctic Ocean, in order of their size.
The Pacific Ocean is the largest ocean. It is spread over one-third of the earth. Mariana Trench, the deepest part of the earth, lies under the Pacific Ocean. The Pacific Ocean is circular in shape. Asia, Australia, North and South Americas surround it.
The Atlantic Ocean is the second largest Ocean in the world. It is ‘S’ shaped. It is flanked by the North and South Americas on the western side, and Europe and Africa on the eastern side. The coastline of Atlantic Ocean is highly indented. This irregular and indented coastline provides ideal location for natural harbours and ports. From the point of view of commerce, it is the busiest Ocean.
The Indian Ocean is the only ocean named after a country, that is, India. The shape of ocean is almost triangular. In the north, it is bound by Asia, in the west by Africa and in the east by Australia.
The Arctic Ocean is located within the Arctic Circle and surrounds the North Pole. It is connected with the Pacific Ocean by a narrow stretch of shallow water known as Bering Strait. It is bound by northern coasts of North America and Eurasia.
The earth is surrounded by a layer of gas called the atmosphere. This thin blanket of air is an integral and important aspect of the planet. It provides us with the air we breathe and protects us from the harmful effects of sun’s rays. The atmosphere extends up to a height of about 1,600 km.
The atmosphere is divided into five layers based on composition, temperature and other properties. These layers starting from earth’s surface are the troposphere, the stratosphere, the mesosphere, the thermosphere and the exosphere.
The atmosphere is composed mainly of nitrogen and oxygen, which make up about 99 per cent of clean, dry air. Nitrogen 78 per cent, oxygen 21 per cent and other gases like carbon dioxide, argon and others comprise 1% by volume.
The density of the atmosphere varies with height. It is maximum at the sea level and decreases rapidly as we go up. The climbers experience problems in breathing due to this decrease in the density of air. The temperature also decreases as we go upwards.
The atmosphere exerts pressure on the earth. This varies from place to place. Some areas experience high pressure and some areas low pressure. Air moves from high pressure to low pressure. Moving air is known as wind.
The biosphere is the narrow zone of contact between the land, water and air. It is in this zone that life exists. All the living organisms including humans are linked to each other and to the biosphere for survival. The organisms in the biosphere may broadly be divided into the plant kingdom and the animal kingdom.
The three domains of the earth interact with each other and affect each other in some way or the other. For example, cutting of forests for fulfilling our needs of wood, or clearing land for agriculture may lead to fast removal of soil from slopes. Similarly earth’s surface may be changed due to natural calamities like earthquakes or tsunamis.
Discharge of waste material into lakes and rivers makes the water unsuitable for human use. It also damages other forms of life. Emission from industries, thermal power plants and vehicles, pollute the air. Carbon dioxide (CO2) is an important constituent of air. But increase in the amount of CO2 leads to increase in global temperatures. This is termed as global warming. There is thus, a need to limit the use of resources of the earth to maintain the balance of nature between the domains of the lithosphere, the atmosphere and the hydrosphere.
Points to Remember
- Mercury, Venus, Earth and Mars are known as’ Inner Planets’ whereas Jupiter, Saturn, Uranus and Neptune are known as “Outer plants”.
- Planets bigger than the earth are Jupiter, Saturn, Uranus and Neptune.
- Earth and Venus have almost same size, hence these two are known as’ Twin planets”
- All planets rotate in the same direction in which they revolve except Venus and Uranus.
- Saturn is surrounded by three luminous, concentric rings.
- Earth has the maximum density of 5.52 in the solar system while the Saturn has the least density of 0.69.
- According to gravity Jupiter stands first followed by Neptune, Uranus, Saturn and Earth.
- Mercury and Venus have no satellite.
- Neptune’s atmosphere has poisonous gases like methane, ammonia, etc.
- Comets revolve around the Sun and when broken are converted into “Meteors”.
- Earth is spherical in shape with compression at the poles and a bulge at the equator. Hence earth is an oblate spheroid or called a Geoid.
A solar day is greater than a sidereal day by 4 minutes.
Each degree of latitude is equals to 111 km.
A person crossing International Date Line from the East to West loses one day.
Mercury is the nearest planet to Sun. Venus is the nearest planet to Earth.
Venus is the hottest planet; its atmosphere contains 97% CO2.
Jupiter is the biggest planet.
V enus is the brightest planet.
Earth is the blue planet.
Mars is the Red planet.
Venus is the Morning and Evening Star.
Pluto is the double planet.
Saturn and Uranus are known as the planets with rings.
Mercury has the maximum diurnal range of temperature.
Saturn has maximum no. of satellites.
Pluto has the most eccentric orbit.
Jupiter is the fastest rotating planet.
Venus is the slowest rotating planet.
Venus has the same period of rotation as revolution.
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 planet.
Mercury, Venus, Earth and Mars are the inner planets.
36.Venus rotates from East to West.
37.Uranus rotates from North to South.
Mercury is the fastest revolving planet.
Pluto is the slowest revolving planet.
Planet revolves around the sun in Anti- clockwise direction.
“Hydra” is the largest constellation.
The nearest galaxy. “Andromeda” is 22, 00,000 Light years away.
Existence of galaxies beyond Milky Way was first demonstrated by Edwin Hubble.
Galaxies are also called “Islands of universe”