Hello students, in this blog you can find important summary notes from the Chapter 17, Science , NCERT Book of Class 8. These notes can be used for preparation of various school Competitive Exams, Olympiads and also developing strong Fundamentals.
1. Celestial objects : The stars, the planets, the moon and many other objects in the sky are called celestial objects.
2. Astronomy : The study of celestial objects and associated phenomena is called astronomy.
3. Passage of the Sun, stars, moon and planets in the sky helped our ancestors to devise calenders and almanacs.
4. Full moon day : The day on which the whole disc of the moon is visible is known as the full moon day.
5. New moon day : After the full moon day, every night the size of the bright part of the moon appears to become thinner and thinner. On the fifteenth day the moon is not visible, this day is known as the new moon day.
6. Crescent moon : The next day of new moon day, only a small portion of the moon appears in the sky, this is known as the crescent moon.
7. Phases of the moon : The various shapes of the bright part of the moon seen during a month are called phases of the moon.
8. Diwali is celebrated on the new moon day; Budh Poornima and Guru Nanak’s birthday are celebrated on full moon day; Maha Shivratri
is celebrated on thirteenth night of waning moon; Eid- ul-Fitr is observed on the day following the sighting of crescent moon.
9. Month : The time period between one full moon to the next full moon is slightly longer than 29 days. In many calendars this period is called a month.
10. The moon does not produce its own light, whereas the Sun and other stars do.
11. We see the moon because the sunlight falling on it gets reflected towards us.
12. The Moon revolves around the Earth.
13. The Earth along with the moon, revolves around the Sun.
14. We never see the back side of the moon from the Earth.
15. The moon completes one rotation on its axis as it completes one revolution around the Earth.
16. The moon has no atmosphere. It has no water.
17. You cannot hear any sound on moon, as there is no atmosphere (medium).
18. On July 21, 1969 (Indian time) the American astronaut, Neil Armstrong, landed on the moon for the first time, followed by Edwin
19. The Sun is also a star.
20. The Sun is nearly 150 million km away from the Earth.
21. The next nearest star is Proxima Centauri.
22. Large distances are expressed in unit known as light year. It is the distance travelled by light in one year.
23. Speed of light is about 300,000 km per second.
24. The distance of the Sun from the Earth may be said to be about 8 light minutes.
25. The stars are present in the sky during the day-time also. However, they are not visible because of the bright sunlight during the day.
26. Stars appear to move from east to west, it means that the Earth, rotates from west to east.
27. Earth rotates from west to east on its axis.
28. There is a star, the pole star, which is situated in the direction of the earth’s axis. It does not appear to move.
29. Constellation : The stars forming a group that has a recognisable shape is called a constellation.
30. Ursa Major : One of the most famous constellations which you can see during summer time in the early part of the night is Ursa Major. It is also known as the Big Dipper, the Great Bear or the Saptarshi.
31. The constellation appears to move in the sky from east to west.
32. We can locate the Pole Star with the help of Ursa Major.
33. The Pole star is not visible from the southern hemisphere.
34. Some of the northern constellations like Ursa Major may also not be visible from some points in the southern hemisphere.
35. Orion is another well-known constellation that can be seen during
winter in the late evenings.
36. Orion is also called the Hunter.
37. The star Sirius, is the brightest star in the sky, located close to Orion.
38. Cassiopeia is another prominent constellation in the northern sky. It is visible during winter in the early part of the night. It looks like a distorted letter W or M.