Solar System
Solar System : The sun, nine planets, moons of the planets, meteors, meteorites, comets, etc. are all the members of solar system. All the members of the solar system revolve round the sun.
Some Facts about Solar System
(a) The sun is the centre of the solar system. It is a star and nearest to the earth.
(b) It gives heat, light and energy to the earth.
(c) The sun consists of hot burning gases—hydrogen and helium.
(d) The surface temperature of the sun is 6000oC and its core temperature is 1,40,000,00oC.
(e) Energy produced by the sun is by nuclear fusion process in which hydrogen is converted into helium.
(f) The diameter of the sun is about 109 times that of the earth.
(g) The distance of the sun is about 150 million km. from the earth. Light takes about 8.5 minutes to reach the earth from the sun.
(h) The sun is a medium sized star.
Planets
There are nine planets—
1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn
7. Uranus
8. Neptune
9. Pluto
An easy way to remember nine planets is to remember the following sentence :
“My Very Elegent Mother Just Showed Us Nine Planets.”
First alphabet of each word stands for the planets e.g.
My—M—Mercury
Very—V—Venus
Elegent—E—Earth
Mother—M—Mars
Just—J—Jupiter
Showed—S—Saturn
Us—U—Uranus
Nine—N—Neptune
Planets—P—Pluto.
A brief description of each planet is given below.
1. Mercury
The Innermost Planet
Mercury is the closest planet to the sun. Its extreme surface temperatures are—180oC to 400oC.
The days on mercury are 58 days, 15 hours, 30 minutes long.
Mercury completes one rotation in about 58 days.
Length of the year is 87.97 days. Mercury is 58 million km from the sun (39% of that of the earth).
Mercury does not have any satellite.
2. Venus
The Veiled Planet
As per the distance, Venus is the second planet from the sun. The earth is closer to Venus. Its size and mass is similar to earth. It is known as ‘earth’s twin.’
Next to moon, it is the brightest object in the night sky. It is easy to locate it in the night sky.
It is covered with thick clouds, so it is called veiled planet. The atmosphere mainly consists of carbondioxide which traps sun’s heat and make the temperature of the surface as high as 450oC.
It is also called evening star because it is to be seen first in the western night sky. It is also seen in the morning in eastern sky that is why it is known as morning star.
Average temperature of the surface of the Venus is 450oC.
The day on Venus lasts for 243 days, 14 minutes. It spins opposite to earth i.e. clockwise.
Year lasts for 224.7 days. Its distance from the sun is 108 million km.
It does not have any satellite.
3. Earth
The Blue Planet
In all the inner planets, earth is the largest. It is the fifth largest planet in the solar system and third in distance from the sun. It is known as blue planet because it has lot of water.
Earth is the only planet which has life on it. Earth has more than one million different kinds of animals and more than 350,000 types of plants. Air, water and vegetation makes life possible on earth.
Average temperature of the surface—14oC.
Length of the year—365.25 days.
Length of the day—23 hours, 56 minutes, 4 seconds.
Distance from the Sun—150 million km.
Satellites—One (Moon).
Earth has water which is an important substance for the life to exist on earth. Life began on earth in oceans some 3000 million years ago.
Earth has large quantities of oxygen in combined and free state. This gas is essential to support all forms of life.
Earth has a blanket of air called atmosphere. Air is essential for the existence of life. It prevents extremes of temperature.
Atmosphere cuts off sun’s radiations mainly ozone, which is a dangerous gas for living beings.
Water and air present on earth support life.
Moon
Earth has only one satellite called moon.
Size of the moon is 3476 km in diameter.
It is about 384,000 km away from the earth.
Surface temperature of moon—extremes (–173oC to 127oC).
Moon takes 29 days, 5 hours for the rotation around the earth.
Eclipse of Moon (Lunar Eclipse)
Lunar eclipse takes place when earth comes in between the sun and the moon and sun, earth and moon are in a straight line with the earth in between the sun and the moon.
The shadow of the earth falls on the moon.
Eclipse of Sun (Solar Eclipse)
A solar eclipse occurs when the sun, earth and moon are in a straight line with the moon positioned in between the sun and the moon.
The shadow of the moon is cast on the earth.
Phases of the moon
Phases of the moon means changing of size of the moon.
(a) New Moon : On this day the moon is between the earth and the sun, the part of the moon facing the earth is in darkness.
(b) Waxing Crescent : After three days of new moon, a thin bright surface of the moon is visible from the earth.
(c) First Quarter : After seven days of the new moon, half of the moon appears luminious.
(d) Waxing Gibbous : On 10th day moon appears more than half luminious.
(e) Full Moon : On 14th day, the moon shows fully illuminated surface.
(f) Waning Gibbous : On 17th day after new moon the waning starts.
(g) Last Quarter : On 21st day after new moon, the moon again appears half circle.
(h) Waning Crescent : After 25th day after the new moon waning crescent starts.
On 28th day, again the new moon occurs. This cycle repeats every months.
4. Mars
The Red Planet
Mars has iron-rich red soil and pink sky which gives it the name, ‘Red Planet’.
Since rotation time on its axis and the inclination of its exis is very similar to that of the Earth, Mars has seasons similar to that of the Earth. But of its greater distance from the Sun, its seasons are cooler and twice as long as those on Earth.
Its white polar caps are visible through the telescope. They are made up of frozen water ice, and carbon dioxide ice. The size of the these polar caps shows seasonal changes.
With the onset of winter the polar cap expands, occasionally extending halfway to the Equator. They diminish in size in summer.
Average Surface temperature :–25oC.
Length of day : 24 hours, 37 minutes.
Length of year : 1 year and 321.73 days.
Distance from the Sun : 228 million km (1.5 times that of Earth)
Satellite : It has two satellites. These are Phobos and Deimos (Phobos, meaning terror. It was named after the mythical servant of the god Mars.)
Discovered : They were discovered in 1877.
5. Jupiter
The Giant Planet
Jupiter is the largest planet of the Solar System. About 1,300 Earth-sized spheres could fit within this planet.
Average Surface temperature :–148oC.
Length of day : 9 hours, 56 minutes.
Length of year : 11 years and 315 days.
Distance from the Sun : 778 million km (5.2 times that of Earth)
Satellites : 16 Satellites
Names : Ganymede, Callisto, lo and Europa (named after the mythological love partners of Jupiter). They are known as the Galilean moons because they were first observed by Galileo.
Size : Diameter ranges from 3000 km to 5000 km.
Discovered : Observed in 1610 by Galileo Galilei first.
6. Saturn
The Jewel Planet
Saturn is the second largest planet and the most beautiful in the Solar System mainly because of its spectacular rings which are made up of ice and ice-covered dust particles. The other giant planets also have rings, but Saturn’s rings are the brightest and most complex.
Saturn does not have a solid surface. It is made up of gases with a very low density. Placed in a large enough ocean it has 95 times the mass of the Earth.
Titan is the largest satellite of saturn in the Solar System. It is bigger than the planet Mercury!
Average Surface temperature :–178oC
Length of day : 10 hours, 41 minutes
Length of year : 29 years and 167.25 days.
Distance from the Sun : 1,400 million km (9.6 times that of Earth).
Satellites : 18 known (22 or more expected)
Satellites
Names : Titan, Rhea, Iapetus, Dione, Tethys (they are named after Greek giants of superhuman strength.
Size : Diameter ranges from 5000 km to 10,000 km.
Discovered : These were discovered between 1655 and 1684.
7. Uranus
A Planet on its Side
This planet is about four times the size of Earth. Like Jupiter and Saturn, this planet is made up of gases, has rings and many satellites that move round it. This planet looks greenish in colour because the methane gas present absorb the red colours from the sunlight.
Average Surface temperature :– 213oC.
Length of day : 16 hours, 48 minutes. It spins on its side, clockwise, opposite to that of Earth.
Length of year : 84 years and 3.65 days.
Distance from the Sun : 2,900 million km (19.2 times that of Earth).
Satellites : 15 (fifteen).
Satellites
Names : Titania, Oberon, Umbriel, Ariel, Miranda are the main satellites of the Uranus. These are named after characters from William Shakespeare’s plays who have names of Greek origin.
Size : Diameter ranges from 5000 km to 1000 km.
Discovered : These were discovered between 1787 and 1948.
8. Neptune
The Last Giant
Naptune is very similar to Uranus and almost of the the same size as Uranus, slightly smaller.
Like Uranus, its greenish colour is due to the presence of small amount of methane. It is also made up of gases. It has a system of rings. It is colder because it is farther from the Sun.
Average Surface temperature :– 216oC.
Length of day : 16 hours, 3 minutes.
Length of year : 164 years and 288.54 days.
Distance from the Sun : 4,500 million km (30.1 times that of Earth).
Satellites
Names : Triton (trumpeter of Neptune), Neried (nymph of the Mediterranean Sea).
Size : Diameter ranges from 300 km to 3000 km.
Discovered : These were discovered between 1787 and 1948.
9. Pluto
The Outermost Planet
It is the smallest, coldest and the outermost distant planet in the Solar System.
Pluto’s orbit is unusual. It is highly elongated and tilted at an angle of 17o as compared to the orbits of the rest of the planets. It moves closer to the Sun than Neptune. So for some time, Neptune is the most distant planet in the Solar System.
Its satellite is unusually large. Besides this, there are other peculiarities about Pluto that make some astronomers speculate that perhaps Pluto is an escaped satellite of Neptune.
Compared to Uranus and Neptune, Pluto seems to be made of solid rocky material. Pluto is a frozen and dark planet. The Sun would look just like a very bright star from it.
Average Surface temperature : –223oC.
Length of day : 6 days, 9 hours 17 minutes.
Length of year : 248 years and 182 days.
Distance from the Sun : 5,900 million km (39.4 times that of Earth)
Satellites : 1 Satellite
Name : Charon considered as son of Pluto.
Size : 1,160 km diameter
Discovered : 1978
Asteroids
Asteroids are the minor planets. They are rocky planetoids and revolve round the Sun, mostly between the orbits of Mars and Jupiter. This area is known as the asteroid belt. Till today more than 5000 asteroids have been identified and catalogued.
Asteroids appear in all sizes. The larger ones bodies are spherical in shape while the smaller ones are elongated and irregular.
Regardless of size and shape, all asteroids rotate on their axes every 5 to 20 hours. Certain asteroids have their satellites.
Asteroids also exist elsewhere in the Solar System. Trojan asteroids can be found in two clouds moving in the orbit of Jupiter, one moving ahead of it and the other moving behind it. In 1977, one asteroid Chiron was observed in an orbit between the orbits of Saturn and Uranus.
Meteors and Meteorites
It has been observed that when asteroids collide with one another, fragments of rocks may break off. These fragments fall towards the Earth. These objects are called meteors.
Meteors are usually small in size and burn up in the Earth’s atmosphere before they reach the Earth’s surface.
When meteors are quite large and do not burn up completely, they hit the Earth’s surface and are known as Meteorites.
All meteorites are believed to originate in the asteroid belt, and due to collisions they fall towards the Earth and the Earth’s gravity attracts them to its surface.
Comets
Comets are among the most spectacular and unpredictable heavenly objects of the Solar System.
Comets revolve round the Sun in different orbits but their orbits are big elongated ellipses that it takes them hundreds and sometimes thousands of years to complete one revolution around the Sun.
Comets consists of frozen gases having rocky and metallic material. They can be compared to large dirty snowballs.
The comet becomes visible when it travels close to the Sun. Its ice melts and the gas and dust is swept back into a tail. The tail always points away from the Sun.
Comet Features : A comet consists of a long, luminous tail. But this is visible only when the comet’s orbit passes close to the Sun. It also has a head. When the comet travels close to the Sun, the ice melts to a head of gas called a coma.
The Sun’s radiation sweeps this into a gas tail. Dust particles are also swept back to form a dust tail. Halleys comet is the biggest one and visible after every 76 years. It became visible in 1986, which was seen by thousands of experts all over the world.
Stars
Stars are the bright objects in the night sky. They vary in size.
They are heavenly bodies composed of hot burning gases, and thus shining by their own light.
Stars seem to be fixed with respect to each other, maintaining the same pattern in the sky year after year. In fact they are in constant motion but they are at such great distance that relative changes in position become noticable only over the centuries.
Alpha Centaury : It is the nearest star to the Earth after the Sun. It is about 4.3 light years away from the earth [also called Proxima Centauri].
If we watch night sky at regular intervals throughout the night and some prominent stars observed, it will be noticed that they seem to rise in the east and set in the west just like the Sun and Moon. That is because the Earth rotates from west to east. All stars except the Pole Star appear to move from east to west.
Star Facts
1. It is believed that there are 1022 stars in the Universe.
2. About 8000 stars are visible from the Earth by the naked eye.
3. Out of this, 4000 stars are visible in the Northern Hemisphere and 4000 in the Southern Hemisphere.
4. In either hemisphere, 2000 stars are visible at any given time. The other 2000 are located in the day-time sky and are not visible due to the brightness of the Sun.
The Celestial Sphere and the Pole Star : The celestial north and south poles are in the same line as the terrestrial north and south poles. The celestial north pole is very close to a bright star Polaris (pole star), also known as the North Star. It appears as if all the stars rotate around the North Star in the Northern Hemisphere. The North Star does not move because it, like the North Pole, is the centre around which the stars rotate. To the observer at the Equator, the North Star is on the horizon.
1. Finding the Northern Direction : For every 111 km of northward travel, the North Star appears 1 degree above the horizon, until it is 90 degrees over the North Pole. 2. Thus, the North Star can be used to find the north direction in the night.
2. Finding the Latitude : The latitude of a place is the angle of elevation of the North Star. For example, if the elevation of the North Star is 35o at some place, it means that the latitude of that place is 35o North.
The North Star is mainly useful to find direction by sailors and travellers in deserts.
Red Giant Star : As fusion continues in the interior of the star, more and more hydrogen is converted into helium. After some time, therefore the matter in its core would consist mainly of helium. However, in the outer of the core has been converted into helium, fusion in that region stops. When this happens the pressure inside the core drops and the core begins to contract again under gravitational force. The fusion reactions in the shell, however, continue and the shell begins to expand thereby increasing its surface area and reducing the intensity of radiated energy. The star now beings to change colour and becomes red. This phase in the star’s life is called the red giant phase. The star is then called a red giant star.
White Dwarf Star : Those stars whose mass is equal to that of the sun. Such a star would lose its expanding shell. The core left behind would gradually condense into an extremely dense ball of matter. Thus resulting his temperatures in its interior would then begin to convert helium into elements, by fusion reactions. The energy liberated by the fusion would make this small core glow as a white dwarf star, as long as it lasts before fading into a dense lump.
Protostar : It is highly condensend cloud of gases (mainly hydrogen and helium) formed by the gravitational contraction of gases present in the galaxy.
Supernova : These are the super giant stars in which the rate of energy production has become high and these are on the verge of explosion. It is also called exploiding star.
Black Hole : It is an infinitely dense object with a strong gravitational field so that even light cannot escape from its surface.
Neutron Star : The extremely dense lump of mass left behind after Supernova explosion. It consists of matter mainly in the form of neutrons.
Pulsar : A spinning neutron star emits radio waves and is called a pulsar.
Constellations
The constellations enable astronomers to identify the position of the stars.
These constellations were named in honour of mythological characters. They hardly bear resemblance to the names they are given.
Today, 88 constellations are recognised.
Some well-known, with their Indian names are given below:
1. Ursa Major (Great Bear) Saptarishi
2. Ursa Minor (Little Bear) Dhruva Matsya
3. Orion (Hunter) Mirga
4. Draco (Dragon) Kaleya
5. Scorpio Vrishchika
Galaxy : A large cluster of stars, dust and light gases bound together by their own gravity is called a galaxy. It is a flattened system of different shapes and sizes. Several galaxies of the order make up the universe.
Earth’s Galaxy The Milky Way
The Milky Way or Akash Ganga is a large spiral-shaped galaxy. It spans about 100,000 light-years across and is about 10,000 light years thick at the centre.
It is called the Milky Way because it appears milky due to glowing light of billions of stars. With his telescope, Galileo discovered this band of light was produced by countless individual stars which the naked eye cannot resolve.
Light-Year : The big distances in outer space are measured in light years.
A light year is the distance light travels in one year at the speed of 300,000 km per second.
One light-year is equal to 9,461,000,000,000 km.
Andromeda : Earth’s Closest Galactic Neighbour
Andromeda is a spiral galaxy. In terms of the entire universe, it is our closest neighbour.
It appears as a diffuse patch of light and contains millions of stars. It is the farthest object that can be seen with the naked eye.
Along with the Milky Way, it belongs to a group of galaxies known as the Local Group, which in turn is part of the Virgo Cluster of groups.
They found that like stars, Galaxies are grouped into clusters. Some clusters contain thousands of galaxies.
About 30 galaxies, along with the Milky Way and the Andromeda are grouped together in one cluster called the Local Group.
Clusters are grouped together into superclusters, which are spread randomly throughout the universe.
Nebulae
Nebulae are very big interstellar clouds of gas and dust. They appear as faint, misty patches of light over the sky. They appear either as bright luminous clouds or as dark patches against a brighter background.
A nebula depends for its luminosity upon the presence of stars that are either close to it or are contained in it. If the stars are extremely hot, the hydrogen in the nebula is ionized and emits a certain amount of light of its own. If a star is less hot, the nebula shines only by reflection. If there are no suitable stars, the nebula does not shine at all. It remains dark and can be detected only because it blots out the light of the stars beyond.
Origin of Earth
The origin of earth has been explained by Big Bang theory. Earth came into existence some 4.6 billion years ago as a result of a big explosion called Big Bang. It took place some 15 billion years ago.
Almost a billion year after Big Bang, stars, dust and gases clustered together to form galaxies. The Milky Way galaxy which was formed after 5 billion years of the explosion gave birth to solar system. In solar system a planets, comets, moons etc. came into existence. Earth was one planet which has life.
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