Planets of our Solar system , All details in English.
Planets of our Solar system .
Written by Manohar Avinash
The name planet has been given to all those (bright) heavenly bodies that revolve round the sun. They look like stars but they do not twinkle. We now know that planets do not have any light of their own. Their observed brightness is only due to the light of the sun reflected by them. 
There are eight planets in our solar system. They move in elliptical-shaped paths called orbits, around the sun. The eight planets of our solar system, in increasing order of distances from the sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
The planets, relatively 'nearer' to the sun have features that are quite different from those which are 'far-off'. We, therefore, find it convenient to divide the planets into two categories:
1. The Terrestrial planets
2. The Jovian planets
Mercury, Venus, Earth and Mars are the Terrestrial planets. They have solid and rocky surfaces.
The Jovian planets are Jupiter, Saturn, Uranus and Neptune. These planets are very large in size and are made up largely of gases.
We now talk about all these planets in some detail.
1) Mercury ( Budh)
Mercury lies closer to the sun than any other planet. It is a dry, hot and virtually airless planet. It has craters like the moon, but its interior is similar to that of the earth. Like the earth, its interior contains iron and other heavy elements. 
Mercury is much smaller in size than the earth. It is occasionally visible just before sunrise, or immediately after sunset. Hence, it is also known as the morning or evening star. Being close to the sun, it takes only 88 earth days to go once around the sun.
Do you know?
A day, for a planet, equals the time taken by it to complete one rotation around its own axis. A year, on the other hand, equals the time taken by it to complete one revolution (in its orbit) around the Sun!
A 'day' on mercury equals nearly 59 earth days. The 'year' for this planet is 88 earth days. The Mercury Year is, thus, only (nearly) 1.5 times its day.
2) Venus ( Shukra)
Venus is the brightest object in our sky after the sun and the moon. Its bright appearance is due to its cloudy atmosphere which reflects almost three-fourth of the sunlight falling on it. Venus is almost the same size as the earth but rotates relatively slowly around its axis. It rotates from east to west while the earth rotates from west to east. It has no moon or satellite of its own.
Venus is even hotter than mercury though it is relatively farther away from the sun. This is because of the high percentage of carbon dioxide in its atmosphere. This gas traps most of the sun's heat falling on it. This is due to the greenhouse effect. Venus is also known as a morning or evening star as it is usually visible only during these times. It also shows phases like the moon.
Do you know?
A 'day' on Venus equals about 243 earth days. However, the 'year' for Venus is only 224.7 earth days. The day on Venus is, therefore, longer than its year!
The earth is a very unique and special planet of our solar system, Like the other planets, the earth not only revolves round the sun but also rotates about an axis of its own. The portion of the earth facing the sun at any time, has day; the other portion, facing away has night. As the earth rotates on its axis, 'day and night' follow one another. The axis of rotation of the earth is known to be tilted with respect to its orbit. It completes one revolution around the sun in nearly 365¼ days. When the northern hemisphere is tilted towards the sun, View of Earth from Moon it is summer there. At that time, it is winter in the southern hemisphere. The reverse happens when the northern hemisphere is tilted away from the sun.
Autumn and spring occur when the earth is in between these two extreme positions in its orbit.
From outer space, the earth appears blue and green due to the reflection of light from the water and landmasses on its surface. It has a thin atmosphere. Though thin, this atmosphere plays a very vital role in protecting and preserving life on the earth. It protects us from being hit by smaller bodies of the solar system. It has an ozone layer, which absorbs the ultraviolet radiation from the sun and protects us from its harmful biological effects. The atmosphere also acts like a natural greenhouse. This keeps the temperature of the earth in the range suitable for the continuation of life.
 |
| Change of seasons |
It is no wonder that earth is the only planet in the solar system that can sustain life on its surface. It fulfills and meets the conditions needed for development and sustenance of life. We can summerise these conditions as:
1. the right size and right distance from the sun so that it has the optimum temperature range and gravity.
2. presence of water on its surface.
3. suitable atmosphere and a blanket of ozone layer.
4) Mars (Mangal)
Mars usually appears reddish in colour, hence, it is also often known as the red planet. Its surface resembles a cold, high altitude desert. Its atmosphere consists primarily of carbon dioxide, along with small amounts of nitrogen, oxygen, water vapour and other gases. Its surface temperature and surface pressure both are very low. These conditions make it unlikely for water to exist in a liquid state on this planet.
The diameter of Mars is only a little more than half of that of earth. Its mass is, however, only one-tenth of that of the earth. Mars, therefore, has a low average density as compared to the earth.
Mars has two natural satellites, or moons named Phobos and Deimos.
Do you know?
NASA's mission of Mars has recently given evidence of presence of water and some elementary form of life on it, long ago. Further investigations are still on. There are plans of having a manned mission on Mars around the year, 2020.
5) Jupiter ( brihaspati)
Jupiter is the largest of all planets. Its volume is 1,300 times more than that of the earth. It shows its own colourful bands. These are believed to be due to its strong atmospheric currents and the dense cloud-cover around it.
Jupiter consists mainly of hydrogen and helium in gaseous form. Its cloud-cover is made up of methane, in gaseous form, with
some ammonia in crystalline form. Till date, Jupiter is known to have 79* moons or satellites. Further investigation may reveal it to have even more moons.
Do you know?
Days go by quickly on Jupiter. They last just 9 hours 50 minutes as it rotates very fast on its axis. But it takes a long time to go round the Sun. Hence, a year on Jupiter is much longer than that on the earth. One 'Jupiter Year' equals nearly twelve earth years.
But for the Sun, Jupiter is the biggest and the heaviest member of the solar family. Its mass, in fact, is more than double (nearly 2.5 times) of the sum total of the masses of all the other planets taken together.
6) Saturn ( shani)
 
Saturn is quite similar to Jupiter in size, mass and composition. It is the second largest planet of the solar family. It is distinguished by its very unique and special system of rings. These rings give it a beautiful appearance. These rings can be seen clearly only with the help of a telescope. Saturn is known to have 82* natural satellites or moons of its own.
7) Uranus (Arun)
This planet is observed to have blue-green colours. This is believed to be because of the presence of Uranus methane gas in its cold, clear atmosphere. Its northern hemisphere remains in a four-decade long period of darkness because of the way the planet rotates. So far 27* satellites or moons of Uranus have been discovered.
8) Neptune (Varun)
Neptune is very far away from the sun and is visible only through a telescope. It has been named after the Roman sea god Neptune. Neptune has 14* satellites revolving around it.
We do not have much detailed information about this planet. This is mainly because of its very large distance from the earth as well as from the sun.
*The number of moons of the Jovian planets keeps on changing. With the improvement in observing techniques, many new moons may be discovered.
Thank you for read.
