The stars
Solar system of Class 8
The Stars
Stars are heavenly bodies that are extremely hot and giveout light of their own. Stars are mainly made up of hydrogen. Inside the stars hydrogen is continuously being converted into helium, by fusion reaction and this process releases a tremendous amount of energy which is given out as heat and light. Stars vary in colour depending on their temperatures. The colours are the same as one would observe when a piece of metal is heated. The metal first glows red-hot, then brighter and yellower until it is white-hot. The same happens in the stars but in the reverse order. For example, our sun is a yellow star with a surface temperature of about 6000°C. Stars appear to be moving in the sky from east to west due to the rotation of the earth on its axis from west to east.
Stars twinkle because we look up at the stars through air that is constantly blowing about, so we recieve their light as unsteady and thus they seem to twinkle.
WHY DO STARS APPEAR TO US LIKE POINT OBJECTS ?
The stars, much like our sun are celestial bodies, which continuously emit heat and light. Our sun is a medium size star. It appears bigger to us because it is nearest to the earth. The stars appear to us like points, because they are very far away from the earth. Most of the stars are so much far away, that the light from them takes millions of years to reach the earth.
Example- 1 Why does the distance between any two stars does not change when viewed from the earth ?
Answer: Stars are moving away from each other at a very high speed. However, when viewed from the earth, the distance between them does not seem to change because they are very far away from us. Hence, any change in the distance between them does not become perceptible in few years or few hundreds of years.
Example 2 Why do the stars appear to move from east to west ?
Answer: It is because the earth rotates about its north-south axis from west to east. Thus, due to relative motion, all heavenly bodies (stars, planets, moon) appear to move from east to west.
Example 3 Why does the pole star (polaris or dhruva tara) not change its position in the sky ?
Answer:The Pole star is situated in the direction which is directly above the geographic north-pole of the earth's axis. Thus, its position relative to the earth does not change and hence, it appears stationary.
Example 4 How does the pole star help travellers and sailors at night ?
Answer:The The pole star always points in the north direction. Thus, looking at the position of the pole star during the night, one can easily find the geographic directions and hence take the correct route.
Example 5 Which is the nearest star to the earth ?
Answer:The The star nearest to the earth is the sun itself. The next nearest star is the Alpha Centauri or Proxima Centauri.
Example 6 How far is the sun from the earth if the light from it reaches us in 8.3 light minutes ?
Answer:1 light minute = 300,000 × 60 km
so, 8.3 light minutes = 300,000 × 60 × 8.3 km
= 149,400,000 km
= 150,000,000 km (approx).
so,149.4 million km.
