anyone read in class 8th if read than science note chapter 17 give me plzz
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Phases of the Moon
Moon and it’s different phases
– The various shapes of the illuminated part of the moon as seen from the earth are called as the phases of the moon. The cycle is about 29 days, where it goes from a full moon to a new moon to a full moon.
Phases of the moon
Understanding phases of moon
– The moon does not produce its own light but reflects the light of the Sun. As the moon revolves around the earth, different parts of its surface get illuminated and we see a different shape every day.
Phases of the moon
The Dark Side of the Moon
The part of the moon that always faces away from the earth is called the dark side of the moon.
The moon’s time period for rotation on its axis and revolution around the earth is approximately the same. (≈ 27.3 days). Therefore an observer always sees the same face of the moon from earth.
Surface of the Moon
The surface of the moon is barren and dusty and devoid of water. It has many large craters and high mountains.
The moon’s gravity is 6 times weaker than earth’s. It is so weak that it does not have any atmosphere. That is why we cannot hear on the surface of the moon.
Stars are celestial bodies that emit their own light and heat. Our sun is an example of a star.
Although stars are always present in the sky but are only visible at night due to the absence of sunlight.
They appear as points as they are millions of kilometres away from us. Stars twinkle as their light gets refracted in our atmosphere.
The position of stars keeps changing as seen from the earth’s surface, apart from the Polestar whose position is fixed.
Pole star
The Pole star (or Polaris) is one star whose position seems to be fixed. All other stars seem to move around the Pole Star.
It can be traced using the constellation Ursa Major.
Pole star
Light year
The distance travelled by light in one year is called a light year. It is a measure of distance for celestial objects.
Speed of light \(= 3 \times 108 m/s\)
1 light year \(= 9.46 \times 1012 km\)
The sun is 8 light minutes away from earth.
The distance of Alpha Centauri is 4.3 light years away.
To know more about Light year, visit here.
Constellations
A group of stars that form a recognisable shape in the night sky is called as a constellation. They were devised by ancient men for navigation purposes.
Examples: Ursa major (Great bear), Orion, Leo major
Constellations
To know more about Constellations, visit here.
Introduction to the Solar System
Celestial Objects
– A naturally occurring physical object in the cosmos, outside earth’s atmosphere, is called a celestial body. E.g: Sun, moon