General Awareness Solar System | Questions & Answers | Notes
The sun, moon, stars, planets and other objects in the sky are called heavenly bodies.
The universe is everthing that exists— stars, planets, moons, other heavenly bodies, everything that exists on these heavenly bodies, such as animals and plants on the earth, and the vast empty space in between.
Origin of the Universe (Big Bang Theory.)
Astronomers believe that about 15 billon years ago, all the matter in the universe was gathered into a single mass. Suddenly the mass exploded, sending particles flying in all directions. These particles formed the galaxies with their stars and planets. These galaxies are still flying away from each other because of the explosion. This is called Big Bang theory.
Stars are present in the sky in groups. Each group has billions of stars in it. Such a group of stars is called a galaxy.
The sun, the earth and other planets and all the stars that are seen in the sky belong to a galaxy called the Milky Way, It is a spiral-shaped galaxy with a bulge in the centre. The sun is situated on one of the arms of the spiral.
• Stars are huge spinning balls of hot luminous gases.
• All stars give out their own light.
• Most stars are made up almost entirely of two gases- hydrogen and helium.
• In the centre of the stars, hydrogen atoms combine to form helium atoms.
• The sun is a medium sized star.
• There are about 100 billion (1011) galaxies in the universe, containing an average of 100 billion stars each. Thus total number of stars in the universe is 1022. This number is so large that it is difficult to even imagine it.
• Planets are heavenly bodies that revolve around the sun.
• Thy do not have light of their own. Their surface reflects the light of the sun.
• They are smaller than stars.
Differences between Stars and Planets
|1. Emit their own light
2. Made up of hot gasse
3. When seen from the earth, they twinkle
4. Massive in size
|1. Do not emit their own light
2. Made up of rocks
3. Do not twinkle
4. Smaller then stars
Distances in the Universe
• Sun is 150000000 km away.
• The next nearest star is Proximo Centauri. It is 4.3 light years away.
• Special units are used to measure distances in space called light year.
• A light year is the distance that light travels in one year.
Light travels at speed of about 300000 km/s.
So, 1 light year = speed of light in km/s
x number of seconds in a year = 300000 x 365 x 24x 60 x 60 km = 9500000000000 km. =9.5 x 1012 km
• Astronomers divided the stars into groups and drew imaginary pictures around them, such as that of a hunter or a bear. This made it easier for them to remember the star patterns. Such a group of stars is called a constellation.
• The shape of a constellation alway remains the same.
• Constellations appear to move from east to west.
• Today 88 constellations are recognized by astronomers.
(1) Ursa Major (Great Bear):
It contains seven bright stars arranged in the form of a big spoon. It is called Big Dipper. It is also called the Great Bear. The Pole Star (Dhruv Tara) is visible towards the north and remains stationary in the sky with respect to the earth. The Pole Star was used by sailors to find the north direction.
(2) Ursa Minor (Little Bear):
This is also a group of seven bright stars similar to the Uras Major.
The Pole Star is a part of this constellation.
(3) Orion :
Orion is also The Hunter. It has seven bright stars and several faint ones. Four bright stars mark the shoulder and legs of the hunter and three stars mark it belt.
This constellation is visible in the winter season and its easy to locate.
This constellation contains seven bright stars. Along with other faint stars, it forms the shape of
a scorpion. It is visible during the summer season.
• Sun is a shining spherical heavenly body around which the planets rotate.
• It is one of some 10,000,000 stars which constitute our galaxy.
• A rather ordinary, middle-age star, the gaseous Sun may reach a temperature of 15.4 million degree Celsius at its core.
• Just 1 square meter of Sun’s surface shines as brightly as 1 million 60 watts bulbs.
• Sun’s hydrogen core converts Hydrogen to Helium at a rate of 600 m tones/second. In doing so it loses 4m tones of its mass/second.
Distance from the Earth –
|149.8 million km|
|Diameter –||1,384,000 km|
|Core temperature –||15,000,000 K|
|Photosphere temperature –||5770 K|
|Rotation as seen from Earth|
|(at the Equator) –||25.38 days|
|(near the Poles) –||33 days|
|Other elements –||2.5%|
|Age –||About 5 billion|
|Expected lifetime of a||About 10 billion|
|normal star –||years|
Above the Photosphere is the Chromosphere, so called because of its reddish colour.
• Beyond this layer is the magnificent corona of the Sun which is visible during eclipses. The, corona is the least dense of the Sun’s layers.
• These are transient dot markings on the visible
surface of SUN caused by a relatively cooler area and seen between 5°C-35° N and S of equator of SUN. •
• The sun spots are about 2000°C cooler than surrounding photosphere.
• The Sun spot have a cycle of 11 years.
• The last Sun spot maximum occurred in 1990, and in 2001.
• It is also called solar erruptions.
• These are powerful erruptions of radiation of SUN and one associated with Sun Spot.
• They occur in chromosphere of Sun.
• It emits intense shortwave radiations that interact with Ionosphere of earth.
• It is a huge gaseous erruption of Sun that is seen in corona of Sun.
• It is associated with Sun spot and effects long distance radio communication of earth.
• It is a persistent stream of charged particles growing out of corona and sweeping over whole solar system.
SUN travels at speed of 250 km/sec and makes one complete rotation about center of Milky way in about 250 million years. This period is called Galactic or cosmic year.
Polar Auroras are two Auroras.
1. Aurora Borealis or Northern Lights
2. Aurora Australias or Southern Lights.
• These are lights that sweep across the sky in waves or streamers or folds. They are very often multi¬coloured and provide one of the finest spectacles in nature.
They occur in the Arctic and the Antarctica regions respectively. But the Northern Lights can be seen as far south as New Orleans in America and the Southern lights as far north as Australia.
• The solar system is tucked away in a corner of the Milky Way at a distance of about 30,000 to 33,000 light years from the centre of the galaxy.
• The solar system originated in a primitive solar nebula – a rotating disc of gas and dust. It is from this rotating disc that planets and rest of the Solar System evolved.
|Planet||Average distance from sun (million km)||Diameter at equator (km)||Mass in relation to earth (Earth = 1)||Time to orbit sun||Time of rotation . on axis||Known number of moons*|
|Mercury||58||4880||0.06||88 days||58 days||0|
|Venus||108||12100||0.32||225 days||243 days||0|
|Earth||150||12800||1||365 days||24 hours||1|
|Mars||228||6800||0.11 •||687 days||24 h 37 m||2|
|Jupiter||778||142800||318||12 years||9 h 55 m||28|
|Saturn||1427||120000||95||29.5 years||10 h 39 m||30|
|Uranus||2871||50800||14.5||84 years||10 h 14 m||21|
|Neptune||4497||48500||17.||165 years||16 h 7 m||8|
|Pluto||5913||3000||0.002||248.5 years||6d9 h||1
Planets of the Solar system
• The solar system is centered on the Sun. It consists of a star called Sun and all the objects or heavenly- bodies revolves around it.
• The Solar System includes 9 planets along with the satellites (not less than 63 moons accompanying the planets) that revolves around most of them.
• The planets of our solar system in order of their distances from the sun are
|Diameter (in kms)||Period of revolution|
|Neptune||49,000||• 164.80 years|
Stars are Suns or self-luminous bodies, situated at enormous distance from the Solar System. The distances of stars are expressed in light years.
. Closest to sun
. Polar regions covered with ice
. No atmosphere and no moon.
. Closest to earth, also called sister planet of earth.
. It is almost of same size as earth.
. It is first planet to . probed by a satellite launched from earth called MARINER-2 by USA.
. Also called Morning Star and Evening Star and brightest apart from Sun and Moon.
. Venus has a atmosphere made up of CO2.
. The surface temperature is 600°C and estimated as hottest planet of the system.
. In Venus, period of revolution around the Sun is shorter than period of rotation about its axis, 243 days once on its axis and 227 days once around the sun.
. Rotates from East to West unlike other planets.
• It is the only planet that contains water, and free
• The internal structure has been determined on the basis of behaviour of earthquake waves that travel to the surface of earth.
• Earth structure is divided into :
Inner core is solid and made up of iron and Ni only. Outer core is molten made up of Iron and Ni. Mantle is mostly solid and made up of silicate minerals. Crust is only 6 to 60 km in thickness.
• Crust is divided into :
Lithosphere, hydrosphere and Biosphere.Biosphere includes whereever life exist in atmosphere and Lithosphere.
• Earth is largest among the planets.
• It is also tilted on its axis by about 2ZlA.
• Nicknamed Red planet
• Longest planet, 70% of volume of 9 planets put together.
• It is the only planet that has own internal source – of energy and emits radio wave.
• Jupiter is largely made up of H2 and is also called Stellar planet
• It has ring like structures like saturn and Uranus.
• Jupiter is also known for huge red spot.
• It controls second largest number of moons which is about 20.
• Second largest planet.
• Density is only about 1/2 of water.
• Farthest planet that is visible to naked eye from earth.
• Glows with yellow light and is believed to contain large amount of NHr
• It has well established rings.
• It controls largest satellite (21).
• Discovered by Sir William Herschel (1781).
• It glows with blue light.
• It is tilted on axis by 19°, i.e. poles turns toward sun alternately.
• Controls 15 satellites.
• Discoverd by J.G. Galle in 1846.
• There are five rings for naptune.
• Neptune glows greenish blue light.
• Neptune controls largest satellite in Solar system called Triton.
Note : Uranus and Naptune are called twins
• It is believed that the Pluto originally was Neptune, but because of gravitational force, it was detached from orbit of Neptune and started revolving around Sun.
• Pluto traces a elongated elliptical orbit of the sun but other traces normal elliptical orbit.
• Pluto has two satellites; one of them Charon is Vi the size of Pluto. In proportion to pluto, the Charon is largest satellite in the solar system.
• Pluto is the only planet of solar system which have not been proved so for by a man made satellite.
• Farthest from the sun.
• Smallest and coldest planet.
Difference between Terrestrial Planets (TP) and Jovian Planets (JP)
1. T.P. are relatively small but J.P. are huge planets.
2.T.P. are dense and earth is densest of all 9 planets. But J.P. are light and Saturn is lightest of all planets.
3.T.P. consist of rocks i.e. rocky structure whereas, J.P. are gaseous planets.
4.T.P. are mostly made up of heavy elements, but J.P. of H2.
5.T.P. rotates slowly on their axis, but J.P. rotates furiously.
6.T.P. controls no or fewer moons, (Earth 1, Mars 2, moons.) but J.P. controls large moons or satellites.
• The international Astronomical Union (IAU) the
official scientific body for astronomical nomenclature, defines a dwarf planet as a celestial body within the Solar System that satisfies these four conditions : ■
(i) It is in orbit around the sun.
(ii) It has sufficient ma’ss for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (near-spherical shape.
(iii) It has not cleared the neighbourhood around its orbit
(iv) It is not a satellite.
• Ceres, Pluto and Eris are the three dwarf planets which are currently recognized by the IAU.
Ceres is the smallest dwarf planet in the Solar System and the only one discovered in the main asteroid belt.
Pluto is the second-largest known dwarf planet in the Solar System and the tenth-largest body observed directly orbiting the Sun.
Eris is the largest known dwarf planet in the solar systemt and the ninth largest body orbiting the Sun directly.
Eris was discovered in 2005 by a Mount Palmoar- based team led by Mike Brown.
• Bodies of dust and foreign gases are called comets.
• These are member of solar system that are usually found orbiting the sun beyond pluto.
• It is a luminous celestial body which moves about the Solar System in elliptical or hyperbolic orbits.
Hyperbolic comets are seen only once and they do not reappear.
Elliptical comets are periodic and their recurrence can be calculated, as in the case of Halley’s comet.
• These are orbiting sun in a region called oortscloud. Some of these comets are known to make periodic visit to centre of solar system and these comets are thought to come from Kuiper Belt that lies just beyond Neptune. So comets are believed to contains frozen ice crystals, dust particles and NH3.
• The comet has a body when it found outside the Jupiter orbit and when it crosses the Jupiter it is in form of head and tail that may stretch millions of km in space. The tail is made up of evaporated particle of frozen ice. The tail of comet is always directed always from sun due to solar winds.
1. Halley’s comet.
It is the most well known comet, which has periodicity of 76 years.
2. Tempel tuttle.
It was first recorded in 1366, and has periodicity in 33 years. It broke up in number of pieces and crashed on Jupiter in 1996.
It was first recorded in 1786, which has shortest known periodicity of 4.3 years.
4. Swift Tuttle Comet.
First recorded in 1862 and has periodicity of 132 years.
5. Shoemaker Levy Comet.
It crashed on Jupiter in 1994.
6. Hale-Bopp Comet.
It has periodicity of 1000 years. It came very close to earth in 1997.
It was first sighted 1996, also came very close to earth in 1998.
• These are minor planets of solar system and are mostly found orbiting sun between Mars and Jupiter and are believed to be fragments of large planet that orbited the sun between Mars and Jupiter.
» Asteroids are very small celestial body. Largest CERES is only 940 in diameter.
• VESTA is brightest as seen from earth.
It is any celestial body, travelling in the interplanetary space in solar system.
These become luminous by friction on entering the Earth’s atmosphere and are popularly called Shooting Stars.
• Meteorite when enters in earth atmosphere, then due to friction meteorite starts burning up and is called Meteorite or shooting star.
• Meteorites are the larger meteors that reach the Earth and become meteorites. All meteorites were meteors when in flight.
When large number of meteors enters the atmosphere and starts burning up, They give the impression of meteorite shower. Meteorite shower normally occurs in August.
When a partly burnt meteorite manages to reach surface of earth, it is called meteoroid. Meteorid may be stony or metallic objects.
The clouds of rarefied gas, which exists stars, glow due to the radiation of the light of the stars. The radiated clouds of rarefied gas are called ‘Nebulae’. Their visibility is hazy and faint.
Drifting particles called interplanetary dust and electrically charged gas called plasma that together make up the interplanetary medium.
• It is only satellite of the earth. Its size is approximately one-fourth of the earth; its weight is about one-eighth of the earth and its orbit is elliptical.
• Maximum distance (apogee) of the moon from the earth is 406,00 km and minimum distance (perigee) is 364,00 km.
• The moon has no atmosphere, no twilight and no sound.
• The light from moon takes 1.3 seconds to reach the earth.
• 1/4th mass of earth.
• 1/6th gravitation force.
Nearly vacuum atmosphere
• Takes 27 days, 7 hours and 43 minutes days to revolve around earth and also about its axis. Due to this only one side of moon can been seen from the earth (54% area).
• The moon contains large number of craters.
Eclipses are the obstruction of the celestial body and the latter casting its shadow on one celestial body are called eclipses.
It is cast when Sun, Moon, Earth are lying an same plane and are in a straight line. A solar eclipse occurs only on new moon day.
The observation of moon and earth casting its shadow on moon when they all are in same plane and lying in straight line. Lunar eclipse occurs only on a full moon day.
• Equinoxes or equal nights (and consequently equal days) are the times when the Sun is shining directly overhead at the Equator.
• March 21 is called the Vernal equinox and September 23 is called the Autumnal equinox.
On June 21, the earth is so located in its orbit that the Sun is overhead on the Tropic of cancer. The Northern hemisphere is tipped towards the Sun, having the longest day, while the Southern hemisphere is tipped away from the Sun, having the shortest day.
On 22 December the earth is in an equivalent position, on the opposite front point, in its orbit. So the Southern Hemisphere is tipped towards the Sun, and the Northern Hemisphere away from it. The Sun is overhead on the Tropic of Capricorn resulting in the shortest day in Northern hemisphere and Longest in Southern Hemisphere.
• Surface area- 510,100,500sq.km
‘ Land surface- 148,950,800 sq.km
• Water surface- 361,149,700 sq.km
‘ Equatorial circumference- 40,066km
‘ Polar circumference- 39,992km
• Equatorial diameter- 12,752km
• Equatorial radius- 6,376km
Mean distance from the Sun– 149,407,000 km
Time of rotation on its axis- 23h, 56m, 4.09 sec
• Period of revolution around the sun- 365 days, 5 hrs 48m, 45.51 sec
• Inclination of the axis from the plane of the ecliptic– 66° 50′
• Escape velocity – 11 km/sec
(i.e. speed necessary to break
away from the earth into outer space)
• Composition Aluminium (0.4%)