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SOLAR SYSTEM
- Our solar system is the only planetary system that is known to us at present though there may be numerous such systems scattered in space.
- The earth is a member planet of our solar system.
- Planets are non – luminous bodies whereas stars are luminous bodies of the universe around us.
- The planets do not have their own light, rather they reflect the light of the stars while the stars have their own light and energy due to thermonuclear reactions wherein hydrogen nuclei combine under intense temperature and pressure to form helium nuclei which release vast amounts of energy.
- The congregation of stars and planets is known as the solar system.
- Like shape consists of 8 planets (e.g. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune) and one star (the sun).
- Besides, there are numerous minor planets (Planetoids or asteroids). All these bodies revolve around the sun almost in the same plane and in the same direction along the near-circular elliptical orbits.
- Most of the satellites of the planets also revolve in the same direction.
- The planetoids with some exceptions have their orbits between the orbits of Mars and Jupiter.
- The rotatory motion of the planets (except Venus and Uranus) is in the same direction as their revolution around the sun i.e. anticlockwise for one who looks at the earth from the North Pole to the South Pole.
- The diameter of the whole solar system is about 1,173 crore kilometers.
- The earth is about 149,600,000 Km (1.496 away from the sun.
- The diameter and average density of the earth are 12,742km and 5.52 respectively.
- Average distances from the sun, period of orbital revolution, period of rotation, diameter, average density, and the number of satellites of the member planets of our solar system are presented.
PLANETS
THE INNER PLANETS
1. MERCURY
MERCURY is the smallest planet and closest to the Sun.
It has the longest period of rotation and the shortest “year” taking only 88 Earth-days to orbit the sun.
For a long time, astronomers thought that Mercury always kept the same face toward the Sun. But new observations show that the planet rotates once every 58 or 59 days.
It has a very thin atmosphere that cannot support life.
2. VENUS
VENUS is the brightest of all planets because it reflects more of the sun’s light which falls upon it than other planets do.
As its orbit is within the earth, it never gets very far from the sun and it is easily seen after sunset.
It is called the “Evening Star” when it appears in the western sky and the “Morning Star” when it appears in the eastern sky.
The thick atmosphere that hangs over Venus traps the Sun’s energy and helps build up the most furnace-like heat yet found on any planet.
So, with its very high surface temperatures, and its atmosphere consisting largely of carbon dioxide, Venus certainly cannot support life as it exists on earth.
In general, the planets and their satellites rotate from west to east, but Venus rotates on its axis from east to west.
3. THE EARTH
THE EARTH appears as a large greenish-blue disc with its blue oceans and sparkling white polar ice caps.
Our earth’s orbit lies between Mars and Venus.
Its average distance from the Sun is 150 million km.
It takes 23 hours, 56 minutes, and 4 seconds to complete one rotation and 362 days, 5 hours, 48 minutes, and 46 seconds (i.e. approximately 365 ¼ days) to complete its orbit around the Sun. This revolves around the Sun gives us our year.
For convenience, one-quarter of a day is ignored for three years and then an extra day is added to every fourth year to give us our Leap Year of 366 days.
The Earth’s circumference is about 40,000 km and its diameter is 12,756.8 km across the equator and 12,713.8 km across the poles.
Its surface area is about 510 million sq km.
The size of the earth is therefore great but not vast in comparison with other planets such as Jupiter or Saturn.
Our planet has one satellite, the Moon.
4. MARS
MARS is “the Red Planet”, is smaller than the earth, and has a very thin atmosphere and a very small amount of oxygen.
It is farther away from the Sun than the earth and so it is much colder.
It takes 24 hours and 37 minutes to rotate on its axis and 687 days to complete one revolution.
Mars presents its poles alternately to the Sun in the same way that the earth does because its axis is tilted in a similar manner.
Temperatures on Mars range from 2.670C to a low of -700C.
About three-quarters of the planet’s surface is covered with bright reddish or yellowish patches.
THE ASTEROIDS (OR PLANETOIDS)
There is a gap of more than 550 million km between the two (Mars & Jupiter). This gap is filled by millions of tiny planets known as Planetoids or Asteroids.
They are mostly tiny lumps of rocks and altogether about 6,000 of them have been discovered.
The largest, Ceres, has a diameter of 768 km.
In spite of their great numbers, their combined mass is only a fraction (about 1/1000) of the Earth’s mass.
All of them revolve around the sun in the same direction as the planets and their mean period of revolution is 4.5 years.
The orbits of some of the asteroids come within the orbits of all the inner planets.
Hermes, one of the small asteroids has come within 7,76,000 km of the earth
THE OUTER PLANETS
5. JUPITER
JUPITER is the largest planet in the Solar System.
If it were hollow there would be room for thirteen hundred earth inside it.
It is only about 300 times as heavy as the earth, indicating that it must be much less dense. However, its mass is more than twice that of the eight other planets combined.
Jupiter is nearly 780 million km from the Sun.
One special feature of this planet is the Great Red Spot, 30,000 km long and 13,000 km wide.
Jupiter’s upper cloud layers seem to have ammonia and methane, both poisonous gases.
Hydrogen and helium are also probably present.
It is the fastest rotating planet, taking less than 10 hours for rotation.
6. SATURN
SATURN is the sixth planet from the Sun and the second-largest in the solar system.
It is 9 times as large as the earth and is visible to the naked eye.
Scientists say that the rings around Saturn are made up of millions of small bits of rocks and dust moving together around the planet.
Outside the rings there are ten satellites, one of them, called Titan, is the largest known satellite of any planet.
Saturn’s specific gravity is less than 1.0. (If a large ocean were available, Saturn would float in it).
7. URANUS
URANUS has 5 known satellites; one of them is very large.
Uranus is tilted 980 as compared to only 23 1/20 for the earth.
It takes 84 years for revolution so that its south polar regions receive sunlight for 42 years and then the North Pole gets its turn.
8. NEPTUNE
Neptune appears blue in color, has two satellites, and takes nearly 165 years to travel once around the sun.
It has no air and is very cold, dark, and desolate.
HEAVENLY BODIES
COMETS
Comets are the most exciting of the heavenly bodies.
They are quite different from stars or from any of the planets but they are also a part of the Solar System.
They are made up of small icy particles of gas and meteoric fragments.
A well-developed comet has a tail that is always turned away from the Sun.
The head forms the brightest portion of the comet.
The tail which may extend millions of kilometers, even more than the distance of the Earth from the Sun, is made of gases blown out of the comet by the Sun’s rays.
Comets move around the Sun in regular orbits but their orbits are very long oval paths (elongated ellipses).
The orbits of many of the comets are so greatly elongated that it takes them hundreds and sometimes thousands of years to complete one revolution around the Sun.
Halley’s Comet is one of the important comets which visit the earth regularly. It is visible once in 76 years.
METEORS
Meteors enter the earth’s atmosphere with such speed that the heat generated from friction with the air causes them to vaporize with a brief flash of brilliantly glowing gas.
This is very fortunate for they could cause great damage if they fell directly on the earth.
METEORITES
Meteors fragments that reach the ground are known as Meteorites.
They consist of rock, iron, or both combined.
Most of them are quite small but a few weigh many tonnes.
The Great Siberian Meteor of 1908, on reaching the earth, exploded so violently that trees were laid flat out to 50 kilometers from the area of impact.
WHY PLUTO IS NOT A PLANET?
Pluto is called a “dwarf planet”. A dwarf planet orbits the sun just like other planets, but it is smaller. A dwarf planet is so small it cannot clear other objects out of its path.
DWARF PLANET
There are 5 officially recognized dwarf planets in our solar system, they are Ceres, Pluto, Haumea, and Eris.
With the exception of Ceres, which is located in the asteroid belt, the other dwarf planets are found in the outer solar system.
Dwarf planets share many of the same characteristics as planets though there is one significant difference.
- A “dwarf planet” is a celestial body that is in orbit around the Sun,
- has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,
- Has not cleared the neighborhood around its orbit, and
- Is not a satellite.
SHOOTING STARS
A shooting star is a common name for the visible path of a meteoroid as it enters the atmosphere, becoming a meteor. These are not stars at all. They are believed to come from different sources. The majority of them are small fragments like those in the belt of asteroids between Mars and Jupiter.
