Universe
The universe is extremely large which includes everything that exists. The earth, sun, moon, planet, stars, matter, energy all are in the universe.
Light year and cosmic year
The distance that light travels in one year is known as light year. In one year the light travels 95 × 1011 km.
The time taken by the sun to revolve round the galactic centre is called cosmic year. The sun takes 25× 107 years to revolve the round the galactic centre.
Astronomical unit:
Light year is a very large unit of distance used in astronomy. One light year of distance is the distance traveled by light in one year.
One light year = 9.46×1015m= 9.46×1012 km.
Astronomical unit is defined as the mean distance between the sun and the earth.
Astronomical unit= 1.496×1011m=1.496×108km
The solar system:
Our solar system is situated in one corner of the Milky Way galaxy. Solar system is composed of the sun, all the planet, satellite, asteroids, comets and other interplanetary material.
The sun:
The sun lies at the centre of the solar system. Its mass is about 740 times greater than that of the sum of the masses of all the planets. It appears very large because it is near to the earth. Otherwise, it is an average sized star its average diameter is about 13, 82,400 km. Its distance from the earth is about 1.5×108km. Its density is 1.41 while it has been estimated that is average temperature is 10,000 0F. The temperature of core is about 35,000,000 OF. It is 12, 99,370 times bigger than the earth by volume and 3, 32,946 times by mass.
The sun is mainly composed of hydrogen. The nuclear fusion that takes place on the surface of sun is the main source of heat and light energy. Visible light, infra and ultraviolet rays, and other radiations are continuously emitted from the sun. Every matter is found in the stream of charged gaseous ions which produces the solar wind. This solar wind is called plasma. The velocity of solar wind is 500km per second. The age of the sun depends on the quantity of hydrogen.
Planets:
A planet has no light of its own. It shines on receiving the light from the star. As compared to the star these are extremely small. Planets are changing their relative position continuously.
There were nine planet named previously but Pluto is now excluded from the list of the planet. Therefore, there are eight planet in the solar system
Following are the planets in the order of their increasing distance from nearest to the farthest from the sun:
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Some information about the planet:
Mercury is the nearest and Neptune is the farthest from the sun.
Mercury and Venus don't have satellite.
Saturn has maximum number of satellite i,e. 18.
The mean surface temperature of the planet decreases as the distance increases from the sun.
The planets which are nearer to the sun are called inner planet, Mercury, Venus, Earth and Mars are inner planet.
The planets which are farther from the sun are called outer planets; Jupiter, Saturn, Uranus and Neptune are outer planets.
The planets within the orbit of the earth are called interior planet, Mercury and Venus are interior planets.
What are terrestrial planets?
The four inner most planets are mercury, venus, earth and Mars. The collective names for all these planets are called terrestrial planets. This is because all of these planets have some common features with earth. All are small bodies of relatively high density, composed of mainly rock, minerals and metals.
Mercury
Mercury is the closest planet to the sun. it s distance is 0.387 AU. from the sun. It completes revolution of the sun in 88 days. From the earth, it appears as a moving star towards the east in the morning and forwards the west in the evening. It can be seen with naked eye from the earth.
Mercury has no water and atmosphere. Mercury may be the most iron rich planet in the solar system.
Venus
It is the second nearest planet to the sun. It has almost same radius, density and mass as that of the earth. Thus, it is also called twin of the earth. It is the brightest of all the planet. It has atmosphere which consists 96 percent of carbon dioxide. Because of high concentration of carbon dioxide the green house effect is very high on this planet. Thus, it has highest surface temperature 342 OC.
Earth
Earth falls on the third position on the basis of distance from the sun and on the basis of its size it falls in fifth.
Mars
Mars is the fourth closet planet from the sun. Due to thin and transparent atmosphere it has been easier to study the mars than other planets. It makes complete rotation in its own axis in 24 hr, and 37 min.
The surface of mars is blood- red. Due to its red colour, it is given the name Mars. The red colour of the Mars is due to the iron oxide rust on the surface of the planet. It has long canal like structures. The canal like structures of mountains surface of Mars makes scientists for long period of time to find water and life here. Now it is found that they are the mountains ranges and no life exists there.
Jupiter
Jupiter is the largest planet of the solar system. As there is a dense cloud all around the Jupiter, the surface is not clearly visible. It is believed that cloud is formed of frozen methane and carbon dioxide. A red spot is seen in Jupiter's clouds. It is estimated that the spot has about 40,000 km length and 32,000 km breadth. It has been predicted that the red spot is formed due to disorder like atmospheric hurricane.
Saturn
Saturn is the second largest planet in the solar system after Jupiter. However, it is the lightest planet since density of the planet is lowest. Like Jupiter the atmosphere of the Saturn is torn by violent storms. The atmosphere is composed of hydrogen, helium, methane and ammonia.
Saturn is the fastest revolving planet in its axis after Jupiter. It completes one revolution in its axis in 10 hrs 3 min. The most distinguishing
Uranus
Uranus is next to the Saturn. Uranus is composed of gas and liquid. The surface of Uranus is very highly heated. The water on its surface is superheated. This planet is made up of cloud of methane crystals. It is supposed that under the cloud of methane crystals there is liquid water and ammonia.
Neptune
Neptune is a giant blue planet and it is named after its deep blue colour. Hydrogen, helium, neon, silicate and water have been found on its surface. It has a rocky core.
Pluto:
Pluto is excluded from the list of planet because of the following reasons:
- Its unusual revolution in the orbit that intersects the orbit of the Neptune.
- Due to its satellite, Charon with which it forms twin planet.
Asteroids:
Asteroids are very small planetary body made from rock and metal, which revolve round the sun mainly between mars and Jupiter. They are also called minor planet. The sizes of asteroid in diameter are from 900km (Ceres) to less than 1km, but very less are more than 100km diameter. Examples Ceres, Vesta, pallaus
Formation of star
Birth and death of star
Stars are made up of hydrogen, helium and small amounts of other elements. In the space, there is huge mass of hydrogen cloud and dust particles. This cloud of hydrogen gas and dust particles is called nebula. The gases in the nebula begin to contract due to the force of gravitation and this result in the formation of a protostar.
A protostar is the packed matter of hydrogen atoms. Due to gravity of protostar the temperature of its core increases. When temperature becomes hot enough, nuclear fusion takes place in its core. At the centre of the protostar, when temperature reaches at 107K, hydrogen nuclei combine to form a helium nucleus. In this process of nuclear fusion, sufficient heat and light energy is produced to glow brightly. This is a star.
Nebula Normal star
Protostar
Red giant star
White dwarf star
Black hole
Neutron star
The life of a star is determined by the amount of hydrogen it has and its consumption rate. The helium formed during nuclear fusion is collected at the core.
The helium core thus formed starts collapsing due to more gravity and at shell nuclear fusion of hydrogen continues. The average temperature of star is not sufficient to bring the nuclear fusion of helium. Thus, after a long period of time when the core of star is completely filled by the helium the nuclear fusion of hydrogen only takes place on the shell. Due to this, the surface of the star expands greatly and the size of the star increase. This is called red giant star.
The helium core becomes more and more compressed due to gravity until its temperature reaches 100 million degree Celsius. At this temperature, the nuclear fusion of helium takes place. This time helium nuclear fusion will begin producing carbon and oxygen nuclei and tremendous amount of energy. When the super giant star is three times bigger than the sun, the outer shell of the star starts to explode, this explosion is called supernova explosion. Due to supernova explosion the outer mass is scattered and only the core is left.
After supernova explosion, if the mass is less than three times the mass of the sun, the remaining mass forms a neutron star. Neutron stars are stars of extremely high densities. When density is extremely high due to decrease in size because of high gravity the electrons and protons all combine and form neutron. Thus, they are called neutron stars.
After supernova explosion, if the mass is more than three times the mass of the sun, the remaining mass forms black hole. Black holes are the regions of the space from which nothing even the light, can escape. If the original mass of the star becomes more than 5 solar mass (or after supernova remaining mass more than three time sun), the central core goes on contracting even beyond the neutron star. This produces a very strong gravity. Even the light radiation of its own cannot escape from its surface , therefore, it is called black hole.
If the original mass of the star is less than 2 solar mass , after conversion of all the hydrogen into helium, the star soon runs out of hydrogen for the radiation of light and heat and converted into white dwarf star.
What is comet? Name one comet.
Comet is a frozen mass of gas, water and dust particles, which appears as a bright ball of light in the sky with long flowing tail. The most famous comet is the Haley's comet, which comes nearer the earth every 76 years.
What are the main compositions of the comets?
A comet consists of a compact nucleus, which is a lump of ice, no more than a few kilometers in diameter within which are embedded particles of silicate dust and larger rocky fragments. This compact nucleus is surrounded by a cloud of gas called coma from which a tail or tails emerge.
What causes the tail of comet when the comet passes close to the sun?
The tails of comet are made from the ice and the dust particles. When they come closer to the sun, the ice vaporizes and then the comet moves with the high velocity that makes them appear a long tail. When the comet is nearer to the sun, the solar wind blows the tail of comet away, which shines brightly due to sun light.
Some common comets:
Haley, Temple-tutle, Enke, Schwasman washman, Bennet, Shemaker Levy,
The tail of comet points opposite to the sun due to solar wind.
Constellations:
Constellation is defined as the group of stars having definite shape. All together, there are about 88 constellation and 12 out of them are considered as signs of zodiac. Some common constellations are:
Orion ( a hunter with a belt and sword)
Ursa Major (Great bear, saptarishi, contains seven stars making a pattern of plough)
Ursa Minor: (little bear)
Cassiopeia
Perseus
Draco
Cepheus
What is galaxy? How many types of galaxy are there based on shape? Name them.
The collection of thousand billions stars in the sky forming a compact is called galaxy. There are three types of galaxy based on the shape. These are
- Spiral galaxy
- Elliptical galaxy
- Irregular galaxy
In which galaxy does the solar system lie? What is the shape of this galaxy?
The solar system lies in the Milky Way galaxy. The shape of Milky Way galaxy is spiral.
Meteors and meteorites
A small celestial mass of stone or metal, which enter the earth's gravity, is called meteors. Meteors come from outer space as bright shooting stars with tremendous speed and mostly vanish when enter the earth's atmosphere. If the meteors reach the surface of the earth, they are called meteorites.
When meteors stars to fall under the gravity of the earth, they are heated due to friction provided by earth's atmospheric air. When heat is more they star to vaporized and glow brightly. They are also called shooting stars.
There are three types of meteors: Stony, Iron and Stony iron.
They meteorites are the cause of crater on the surface of planet. Especially, meteors fall in large number near the earth's pole.
Difference between galaxy and constellation:
No. | Constellation | No. | Galaxy |
1 | A small group of stars with unchangeable shape is called constellation. | 1 | The collection of thousand billion of stars in the sky forming a compact group is called galaxy. |
2 | There are altogether 88 constellations | 2 | On the basis of shape galaxy are of 3 types, but there are about 1011 galaxies |
Difference between stars and planet:
Star | Planet |
A star has its own light and emits it continuously | A planet has no light of its own. It shines on receiving light from star. |
Stars twinkle at night | Planets don't twinkle at all |
Stars are very big in size | Planets are very small in size. |
Stars don't change their relative position in the sky | Planets are changing their relative positions continuously |
Difference between comet and meteor:
Comet | Meteor |
Comet is a frozen mass of gas, water and dust particles, which revolve round the sun in its orbit | The pieces of stone or metal, which enter the earth's atmosphere are called meteors. |
A comet appears as a bright ball of light in the sky with long flowing tail as comes near the sun. | Meteors come from outer space as bright shooting star with tremendous speed and vanish mostly on earth's atmoshphere. |
It is also called tailed star | It is called shooting star. |
Comets, planets, constellations and satellite:
Comet | Planet | Constellation | Satellite |
Ceres, Vesta, Pallaus | Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune | Ursa Major, Ursa Minor Cassiopeia, Perseus, Draco, Cepheu | Phobo |
