Stars and the Solar System - Exemplar Solutions 3

CBSE Class 8 Science
NCERT Exemplar Solutions

15. A star is ten light years away from the earth. Suppose it brightens up suddenly today. After how much time shall we see this change ?
Ans: We will see the change after 10 years.

16. Meteors are not visible during the daytime. Explain the reason.
Ans: Meteors are very small, star-like objects that are revolving around the sun. They become visible only when, by some chance, they enter the earth's atmosphere. When a meteor enters the earth's atmosphere, it is travelling very fast . . . about 2 miles a second. At such high speeds, it gets heated due to friction with the molecules in the earth's atmosphere. The heat produced is so high that the meteor begins to burn. It glows and evaporate quickly. But its brightness is extremely small compared to that of the sun due to which it is not visible during day time.

17. Why does the moon change its shape daily ?
Ans: The moon changes its shape daily because we see only that part of the moon from which the light of the sun is reflected towards us.

18. Paheli saw the moon through a glass window at 8:00 p.m. She marked the position of the moon on the glass pane. She got up at 4 a.m. in the morning. Will the moon be visible at the same position ?
Ans: No, because the position of the moon keeps changing during the night.