The solar system is made up of the sun and everything that orbits around the sun like planets, moons, comets and meteoroids. Every planet in solar system orbits around the sun in elliptical orbits due to gravitational force. The existence of a solar system in the universe is due to the influence of gravitational force between the members of the solar system. Planets are the heavenly bodies that revolve around the sun. Some of the examples of planets are earth, jupiter, mars, etc. Satellites are the heavenly bodies that revolve around the planets. Some of the examples of satellites are the moon, titan etc. Comets are the small irregular bodies in the solar system that are made up of ice and small amounts of dust and rocks. Asteroids are the small rocks that revolve around the sun.
The sun is the largest object in the solar system. It is a star. It is a ball of fire. Everything in the solar system revolves around the sun. The sun contains about 99.8% of solar system mass. The diameter of the sun is about 13,92,400 km. The mass of sun is about 1.988 \(\times\) 1030 kg. The sun is about 109 times as large as Earth and 333,000 times as massive. The sun is about 15 crore km far from the earth. The temperature of the surface of the sun is about 5400oC and the temperature of its core is about 1,50,00,000oC. The sun is about 4.5 billion years old.
Planets are the heavenly bodies that revolve around the sun. There are eight planets in our solar system, they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune (from order). Among them, Jupiter is the largest planet and Mercury is the smallest planet and Mercury is the nearest planet and Neptune is the farthest planet from the sun. Venus is the hottest planet whereas Neptune is the coldest planet. Pluto is not the planet but it is classified as a dwarf planet. There is an asteroid belt in the solar system that is located between Mars and Jupiter. It is made up of rocks. Those planets that lie inside the asteroid belt are the inner planet and those planets that lie outside the asteroid belt are the outer planet. Mercury, Venus, Earth and Mars are called inner planets and Jupiter, Saturn, Uranus and Neptune are called outer planets. In this note, we discuss the eight planets of solar system which are given below,
|Name of the Planet||Distance from the sun (in km)||Period of revolution(days/years)||Period of rotation(hour, days)||Average diameter(in km)||Mass (kg)||Temperature(K range or average)||Number of satellites|
|Mercury||5.76 \(\times\) 107||87.97 days||58.85 days||4851.2||3.3\(\times\) 1023||100- 700K||0|
|Venus||10.7 \(\times\) 107||224.7days||243.02 days||12035.2||4.87\(\times\) 1024||726K||0|
|Earth||14.88 \(\times\) 107||365.25days||23 hrs.56 min.||12672||5.98\(\times\) 1024||260- 310K||1|
|Mars||22.56 \(\times\) 107||286.98days||24 hrs. 37min. 22 sec||6742.4||6.42\(\times\) 1023||150- 310K||2|
|Jupiter||76.8 \(\times\) 107||12 years||9 hrs. 55 min. 30 sec||1139040||1.90\(\times\) 1027||120K||63|
|Saturn||144 \(\times\) 107||29.5years||10 hrs. 30 min.||115811.2||5.69\(\times\) 1026||88K||60|
|Neptune||288 \(\times\) 107||4years||17 hrs. 14 min. 24 sec||50441.6||8.68\(\times\) 1025||59K||27|
|Uranus||448 \(\times\) 107||164years||16 hrs. 6 min 36 sec.||48972.8||1.02\(\times\) 1026||48K||13|
We see numerous twinkling objects when we see in the clear sky at night. These twinkling objects are known as stars. They are very bright as they have their own sources of light. They are hot and bright luminous objects. Star are the masses of hot gases. There are different shape and sizes of stars. Some are big and some are small. But when we see the clear sky at night, those stars only looks big which are nearer to the earth and those stars looks small that are far away from the earth. The sun is also medium- sized star. It appears big because it is very near to the earth. We get light and heat from the sun. We do not get light and heat from the other star because they are very far from the earth.
Distance of Stars
As we know that, stars are located very far from each other. They are located millions of kilometers far from the earth. So, it is impossible to measure the distance in meter and kilometer. So, the distance between the star and the earth is measured in a light year. The total distance covered by light in one year is called light year. Light travels about 3 lakh kilometers in one second and it covers 9.5 \(\times\) 1012 kilometers in one year.
One light year = Speed of light \(\times\) One year
= 300000 km/s \(\times\) 365 days
= 300000 km/s \(\times\) 365 \(\times\) 24 hours
=300000 km/s \(\times\) 365 \(\times\) 24 hours \(\times\) 60 minutes
=300000 km/s \(\times\) 365 \(\times\) 24 hours \(\times\) 60 minutes \(\times\) 60 seconds
= 9.5 \(\times\) 1012km
Brilliance of Stars
When we see the clear sky at night, we can see stars twinkling. Some stars twinkles with very bright light whereas some stars twinkles with faint light. Different stars have different level of brightness. The brightness or brilliance of star depends on its surface temperature, size and distance from the earth. The distant stars have less brightness whereas the nearer stars have less brightness.
Colours of Stars
When we see in the clear sky at night, all the stars looks same. Some stars may look brighter than others but they all look white in colour. But when we see the sky through the telescope, the stars looks in a different colour. They may be red, orange, yellow, white and blue in colour. The colour of a star depends on its surface temperature and indirectly on its size. The stars with less surface temperature look red and stars with high-temperature looks blue.
|Colour of Star||Temperature|
Structure of Stars
Stars are giant luminous heavenly bodies that are made of hydrogen and helium gases. There are billions of stars in the sky. Stars produce heat and light due to the nuclear fusion that takes place inside the stars. Stars are not permanent because there is continuous change in the composition of stars.
Motion of Stars
Stars do not remain in the same position. One star is in a state of motion with respect to another. Stars change their relative position in the space.
Differences between Planets and Stars
Planets and stars are different from each other. Planets are non- luminous body and stars are the luminous bodies. Planets revolve around the sun whereas stars do not revolve around the sun. Some of the differences between planets and stars are discussed below,
|Planets are the luminous body.||Stars are non- luminous body.|
|Planets do not twinkle.||Stars twinkle at night.|
|Planets have a very low temperature ranging from -330oC to 865oC.||Stars have a very high temperature ranging from 3000oC to 25000oC.|
|They are made of rocks, dust particles, and water vapour.||They are made of hydrogen and helium gases.|
|There are only nine planets in the solar system.|| |
There are billions of stars in the celestial sphere.
|Their diameter ranges from 4851km to 1139040 km.||Most of the stars are big in size but only a few of them are smaller in size.l|
We see millions of stars in the sky. They are at different positions. Some stars are seen bright and some are seen dim. But when we join or arrange the bright stars, special identifiable shapes are formed. They may be shapes of some animals or some objects. These groups of stars, when arranged, form shapes of objects or some animals are known as constellations. Therefore, the constellation can be defined as the small groups of a star that form the pattern or shapes of some objects or animals. Till now, there are 88 constellations named by our astrologist. Out of them, 12 constellations are called zodiac. Some of the common examples of constellations are the Big dipper, Orion, Virgo, Ursa major, Sagittarius etc. These shapes are given names of gods, animals, zoidiac, virgo, heroes etc. by the astrologists. Some of the information about some famous constellations are discussed below,
Identification of Constellations
Since Nepal lies in the northern hemisphere, we can only see the constellations of the northern hemisphere. We cannot see the constellation of the southern hemisphere. The constellation seen in a particular season are not visible in another season as the earth revolves around the sun. For the identification of constellation, at first, we should find the position of two famous constellations of the north pole, Ursa major and Ursa minor. Ursa Major appears like the shape of a question mark. We can also identify other constellation by using sky map or chart of constellations.
Solar system is the family of the sun that includes the sun, eight planets, satellites, asteroids, comets, etc. The names of inner planets are given below,
Those planets which lies outside the asteroid belts are called outer planets. The names of outer planet are given below,
Any three differences between planets and stars are given below in table,
|Planets are non- luminous body.||Stars are luminous body.|
|Planets do not twinkle.||Stars twinkle.|
|Their number is uncountable.||There are eight planet in our solar system.|
Constellations are the groups of stars which do not change their location relative to each other but form a fixed shape. Any four names of constellations are given below,
The names of eight planets on the basis of their position or order is given below,