DAV Class 8 Science Chapter 17 Notes – Stars and Solar System

These DAV Class 8 Science Notes and DAV Class 8 Science Chapter 17 Notes – Stars and Solar System act as excellent revision resources, particularly in preparation for board exams.

Stars and Solar System Class 8 DAV Notes

→ Star: A star is a huge heavenly body which is made up of very hot gases. Sun is the nearest star to the earth. The next nearest star from the earth is Alpha Centauri. It is at a distance of 4.3 light years from the earth.

→ Light year: The distance covered by light in one year is called a light year. One light year is equal to 9.4 x 1012 m.

→ Colour of Stars: The colour of a star depends on its surface temperature. Stars with lower temperature appear red, those with high temperature appear white and the stars with very high temperature appear blue.

→ Pole Star (Dhruv tara): The Pole Star is a star which is visible from the northern hemisphere only. This star is unique because it appears to be fixed at one position in the sky. All other stars appear to revolve around this.

→ Constellations: A group of stars appear to form some kind of pattern. Such groups of stars are called constellations. We can see certain recognizable patterns in different constellations. Examples: Scorpio, Great Bear, Orion, etc.

DAV Class 8 Science Chapter 17 Notes - Stars and Solar System

→ Orion: Orion is one of the prominent constellations. It is visible during summer right from evening till late night. It appears like a hunter. The three most prominent stars in the constellation form the belt of the hunter.

→ The Big Dipper: It is also known as Great Bear, Ursa Major, in Hindi, it is called Saptarishi. There are seven stars in this constellation. It makes the shape of a big ladle. The Pole Star is in line with this constellation.

→ Small Dipper: This is a miniature version of the Big Dipper. The Pole star lies at the handle tip of this constellation.

→ Cassiopeia: This is another prominent constellation in the northern sky. It appears like the English alphabet W or ‘M’. The Cassiopeia and the Big Dipper can never be seen together in the sky.

→ The Moon: The moon is the only natural satellite of the earth. There is no atmosphere on moon. The moon takes 29.5 solar days to make one revolution around the earth. Because of its revolution around the earth, the moon’s apparent shape keeps on changing every day. This is called waxing and waning of the moon.

No moon is visible on a new moon day. This slowly develops into a crescent, then to half moon and finally to the full moon on a full moon day. These are called phases of the moon.

→ Moon’s Surface: Moon’s surface is dusty and barren. There are huge crates on its surface. Many mountain ranges, valleys and lava plains are also present on the moon.
Because of absence of atmosphere, the temperature of moon ranges from 100°C (at noon) to -173°C during night.

→ The Solar System
The sun, various planets, satellites, and other celestial bodies form the solar system.

→ Sun: The sun is a sphere of hot gases. The temperature of the bright disc of the sun is about 6000 K. This is the portion which provides us energy. The radius of the sun is about 100 times the radius of the earth. The mass of the sun is about a million times the mass of the earth.

DAV Class 8 Science Chapter 17 Notes - Stars and Solar System

→ Planets: A celestial body which revolves around a star is called a planet. A planet does not have its own light rather it reflects the light of its parent star. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune are the eight planets in the solar system.

→ Planets can be divided into two categories:
(a) Terrestrial Planets: These are smaller in size and are made up of rocks. Mercury, Venus, Earth and Mars are terrestrial planets.
(b) Jovian Planets: These are very large in size and are mainly made up of gases. Jupiter, Saturn, Uranus and Neptune are the Jovian planets.

→ Mercury: In Hindi, this is known as Budh. Mercury is the nearest planet from the earth. It is a dry, hot and virtually airless planet. Its inner composition is similar to that of earth; as it is composed of iron and other heavy elements. Mercury is the smallest planet.

→ Venus: In Hindi, this is known as Shukra. It is the brightest object in the sky; after the sun and the moon. Venus is hotter than mercury although it is farther away from the sun. This is because of high percentage of carbon dioxide in its atmosphere. Venus appears in the evening sky (during summer) and in the morning sky (during winter). Due to this, it is also called the morning and evening star.

→ Earth: The earth is unique as life is known to exist only on the earth. This is possible because of just the right balance of various gases in the earth’s atmosphere. The earth takes 365.25 days to make one revolution around the sun.

→ Mars: Mars is also called red planet, because of its red appearance. The atmosphere of mars is mainly composed of carbon dioxide; with small amounts of nitrogen, oxygen, water vapour and other gases. The diameter of mars is a little more than half of the diameter of earth. Its mass is one-tenth the mass of the earth. There are two natural satellites of mars, viz. Phobos and Deimos.

→ Jupiter: This is the largest planet in the solar system. Its volume is 1300 times the volume of the earth. Jupiter is mainly composed of hydrogen and helium. Its cloud cover is made up of methane (in gaseous form) and some ammonia in crystalline form. There are 28 moons of Jupiter.

→ Saturn: This is the second largest planet in the solar system. The Saturn is distinguished by rings around it. There are 30 natural satellites of Saturn.

DAV Class 8 Science Chapter 17 Notes - Stars and Solar System

→ Uranus: This is the third largest planet in the solar system. Its diameter is about 4 times the diameter of the earth. The planet appears blue-green in colour because of the presence of methane gas. There are 21 natural satellites of Uranus.

→ Neptune: Neptune is so far from the sun that it is visible only through a telescope. There are 8 natural satellites of Neptune.

→ Minor Bodies in the Solar System

→ Asteroids: These are very small planets or planetoids which are found mainly in a belt between the orbits of Mars and Jupiter. Ceres is the largest asteroid discovered till date.

→ Comets: Comets are relatively small and icy celestial bodies. When a comet comes near the sun, some ice turns into gas. This leaves a long trail which appears as the tail of the comet. Halley’s comet is the best known comet. It appears after every 76 years. It was last seen in 1986 and is expected to pass by the earth again in 2062.

→Meteors and Meteorites: Meteors are relatively small solid bodies which revolve around the sun. Some of them may enter the earth’s atmosphere. When a meteor enters the earth’s atmosphere it burns off because of intense heat which is generated because c’ igh friction. Some meteors are so large that a part of them is able to reach the earth. They are called meteorites.

→ Artificial Satellites: Man-made satellites are called artificial satellites. Artificial satellites usually revolve around the earth in geosynchronous orbits. Artificial satellites perform various tasks; like transmitting radio, telephone and television signals. They send valuable information for weather forecasting, military surveillance and for locating mineral resources.

DAV Class 8 Science Chapter 17 Notes - Stars and Solar System

→ Star : A celestial body which is very large and is composed of very hot gases.

→ Planet : A celestial body which revolves around a star.

→ Satellite : A celestial body which revolves around a planet.

→ Artificial satellite : Man-made satellite.

→ Geosynchronous Orbit: The orbit around the earth in which an artificial satellite remains in a fixed position.

→ Constellation : A group of stars which resemble a familiar shape.

→ Meteor : Very small celestial bodies which revolve around the sun.