8th Class Science Stars and the Solar System Stars

     Introduction

The space including, the celestial bodies and galaxies is called universe. There are millions of galaxies in this universe and each galaxy has billions of stars. Like living things, these stars also have life cycle, take birth and die. The name of our galaxy is Akash-Ganga. Each galaxy consist of stars, the planet, satellites, asteroid, comets, and meteoroids. They are also known as celestial bodies or heavenly bodies. In this chapter, we will discuss about these heavenly bodies.

         Stars

Starsarethe heavenly bodies having light of their own. They continuously emit heat and light. They mostly consist of hydrogen gas. Like Sun, they produce energy by the process of nuclear fusion. In this reaction, the hydrogen present inside the stars are converted into the helium molecules after fusion, with the release of large amount of energy in the form of heat and light. The Sun is also a star, which is nearest to us. It appears much bigger and brighter as compared to other stars. This is because, it is much nearer to us. The intensity of sunlight is very high during the day time. The stars are much bigger as compared to the Sun. Also they emit the light of much higher intensity than the Sun. The nearest star to the earth other than the Sun is Proximo centauri. There are about 10,000 billion stars in this universe. As the Earth moves from east to west, the stars seem to move from east to west too. But there is one star, which appears to be stationary when observed from the pole, it is known as Pole star or Dhruva tara. The pole star appears stationary, because it lies on the axis of rotation of the earth. As the pole star lies on the north pole, it is not visible from the south pole of the earth.

We know that the distance of these stars is very far from the earth, so they cannot be measured with the help of smaller units, such as km. We have to use the larger unit, i.e. light year. One light year is the distance traveled by the light in one year. One light year is equivalent to 9.46 x 10¹² km. It is obtained by multiplying the speed of light with the number of seconds in one year. The light from the Sun takes 8 minutes to reach the earth. The next nearest star, Proxima centauri is 4.3 light year away from the earth. Hence, if a star is n- light years from earth, means that the light takes n years to reach the earth.

      It is found that most of the stars and planets are made up of certain types of gases. These gases are found in large quantity and are lighter in nature, and helps in the formation of stars and planets. Which one of the following is the main gas that helps in the formation of stars and planets?

(a) Hydrogen

(b) Helium

(c) Carbon

(d) Nitrogen

(e) None of these

Answer: (a)

Explanation

Scientific research have shown that, the main gas which is present in almost all the stars is hydrogen.

       The stars are at very large distance from the earth. It takes many years even by the light to reach earth from the stars. Can you name the star which in nearest to the earth other than Sun?

(a) Sirius

(b) Canopus

(c) Arcturus

(d) Proxima-Centuari

(e) None of these

Answer: (d)

Explanation

The nearest star other than Sun, is Proxima centuari.

       Galaxy

Galaxy in which our earth lies is known as Milky Way. All the stars that we see at the night in the sky is just a small part of our milky way. The milkyway is a spiral galaxy and the Sun is located at about 30,000 light years, from the nucleus of the galaxy. It lies on Orion arm of the galaxy.

Like all galaxies, the milky way is held together by gravity. This gravity also holds the stars, gas and dust in orbit around the center of the galaxy. Just as the planets orbit around the Sun, the Sun orbits around the center of the milky way. It takes about 225 million years to complete one revolution around the Milky Way by the Sun.

       There are thousands of galaxies in this universe. Each galaxy has millions of stars, as well as, planets and other celestial bodies. What is the name of galaxy in which earth is present?

(a) Orion

(b) Epic

(c) Milky way

(d) Helene

(e) None of these

Answer: (c)

Explanation

The name of galaxy in which our solar system is Milky Way.

        As the planets revolve around Sun in a fixed orbit, the Sun also revolves around the centre of the Milky Way. The period of revolution of the planets and that of the Sun are different. They take certain fixed period of time to complete one revolution around its orbit. The time taken by the Sun to complete one revolution around the centre of the Milky Way is _______.

(a) 100 million years

(b) 155 million years

(c) 225 million years

(d) 275 million years

(e) None of these

Answer: (c)

Explanation

The time taken by the Sun to complete one revolution around the centre of Milky Way is 225 years..