Chapter 17

Stars and The Solar System

In this article, we shall discuss NCERT Class 8 Science chapter 17 – Stars and the Solar System. Celestial bodies comprise planets, the moon, stars and other heavenly bodies. Astronomy is a discipline of science concerned with the study of celestial bodies and their occurrence. One of the celestial body observations that we may make is the change in the moon's shape every day. The full moon day is when the entire circle of the moon is visible. The moon's phases are the several shapes of the luminous part of the moon observed for a month.

Phases of the Moon

Moon and its different phases

The moon’s phases  are the changing shapes of the elucidated part of the moon as seen from Earth. It takes around 29 days to cycle from a full moon to a new moon to another full moon.

Understanding the Moon's Phases

The moon does not emit its own light, instead reflects the Sun's light. Distinct areas of the moon's surface are illuminated as it rotates around the earth, giving us a different form every day. The side of the moon that faces the sun will be illuminated as it circles around the planet Earth. Due to the sun's brightness, the moon will be illuminated. The moon phases are the various shapes of the lit part of the moon that can be seen from our planet, Earth. Furthermore, each of these stages occurs every 29.5 days.

The Dark Side of the Moon

The moon's rotation on its axis and revolution around the Earth takes about the same amount of time. (It takes 27.3 days). The dark side of the moon is the side of the moon that always faces away from the earth. As a result, a viewer always sees the same face of the moon from Earth.

The Moon's Surface

  • The moon's surface is dry, dusty, and devoid of water. It has a lot of big craters and tall mountains.
  • The gravity on the moon is six times lower than on Earth. 
  • It does not have any atmosphere. That is why humans cannot hear on the moon's surface.

Even though they are millions of kilometres away from us, they look like points. As their light is refracted by our atmosphere, stars sparkle.

Apart from the Polestar, whose position is fixed, the position of the stars changes as seen from the earth's surface.

Star at the North Pole

The Pole Star (or Polaris) is a star that appears to have a stable position. 

The constellation Ursa Major can be used to locate it.

Light year

A light year is the distance travelled by light in one year. It is a distance measurement for celestial objects.

(= 3 times 108 m/s) is the speed of light.

1 light year (= 9.46 x 1012 km) is the distance between two points in space.

The earth is 8 light minutes from the sun.

The distance between Alpha Centauri and Earth is 4.3 light years.

Constellations

A constellation is a group of stars that form a recognisable shape in the night sky. Ancient men created them for the purpose of navigation.

Ursa Major (Great Bear), Orion, and Leo major are some examples.

Celestial Objects

A celestial body is a naturally occurring physical object in the universe outside of the earth's atmosphere. For example, the sun, planets, moon, stars, etc.
They are a part of the vast cosmos we live in, usually rather far from us. Such objects abound in the majestic night sky, and when viewed through a telescope, they reveal intriguing worlds of their own. We cannot see them all with our naked eyes since they are so far away, so we use telescopes to study them. The term celestial body encompasses both known and unknown celestial bodies.

Classification of Celestial Bodies.

  1. Stars
  2. Planets
  3. Satellites
  4. Comets
  5. Asteroids
  6. Meteor and Meteorites
  7. Galaxies

The Solar System

Our solar system is made up of the sun and all of the planets and celestial bodies that rotate around it. There are eight planets in our solar system, as well as an asteroid belt. Pluto is classified as a dwarf planet by the International Astronomical Union.
All planets in the solar system spin in a constant orbit around the sun. Planets that are closer to the sun revolve faster than planets that are farther away.

 

The sun is the closest star to our planet. It produces heat and light on a constant basis.

It is the primary source of heat and light energy for all planets in our solar system.

The Planetary System

Planets are celestial planets that do not produce their own heat or light.

They orbit a star in defined trajectories termed orbits, and the period of revolution is the time it takes to go around the sun once.

A planet also rotates on its own axis, a process known as rotation.

Orbit

A planet's orbit is the fixed path it travels to revolve around the sun.

Mercury

Mercury is our solar system's tiniest planet and the planet closest to the sun.

Due to the brightness of the sun, it is generally covered, however, it can be seen early morning or during dusk.

Venus

In the night sky, Venus is the blazing planet.

It is the planet that is nearest to Earth.

It is called the morning star or evening star because it can be seen before sunrise in the eastern sky and after sunset in the western sky, despite the fact that it is not a star.

The Earth

In our solar system, the Earth is the sole habitable planet. The existence of life on Earth is due to a number of ideal conditions, including the existence of an atmosphere and water, as well as the correct distance from the sun.

As light is reflected off of the landmass and water bodies, the planet appears blue-green from space.

The Moon is the only natural satellite of the Earth.

Seasonal variations are caused by the tilt of the earth's axis of rotation.

Mars

Mars is the fourth planet in the solar system. The reddish iron oxide that coats its surface gives it a reddish colour, giving it the name "Red Planet." There are two natural satellites orbiting Mars.

Jupiter

Jupiter is our solar system's largest planet. It's so large that it can hold 1300 earths. Despite the fact that it is just 318 times heavier than the earth.

There are at least 67 moons orbiting Jupiter.

Jupiter contains a large red spot, which represents a massive storm that has been spinning for years and is twice the size of the Earth.

Asteroids

Asteroids are a vast number of tiny astronomical objects that orbit between Mars and Jupiter's orbits.

In their orbit, they also spin around the sun.

A belt of asteroids is formed when many asteroids collide.

Saturn

Saturn is our solar system's second-largest planet. It is one-of-a-kind since it has thousands of stunning rings.

Saturn has a plethora of moons.

Uranus and Neptune

Uranus is a planet that revolves from west to east. Its axis has a significant tilt, giving the impression that it is spinning on its side.

Neptune is our solar system's eighth and farthest planet. It possesses extremely powerful winds, stronger than any other planet in the solar system.

Comets

Comets are celestial bodies that travel in long elliptical orbits around the sun. They are usually composed of ice, dust, and gases, and have a long tail that points away from the sun.

As a comet approaches the sun, it warms up, ejecting gas jets and forming a massive incandescent head.

Meteors and Meteorites

Meteors are small objects that enter the earth's atmosphere at high speeds. They are mostly remaining fractured asteroids.

The meteor burns and evaporates before it hits the ground due to friction between the atmosphere and the meteor. That's why they appear in the sky as dazzling streaks of light.

When a meteor is large enough to not dissolve in the atmosphere, it can hit the ground. A meteorite is what this is called.

Man-Made Satellites

Artificial satellites are man-made objects launched from Earth that orbit the planet at a considerably closer distance than natural satellites.

They're used for a variety of things, including remote sensing, weather forecasting, and signal transmission. INSAT, IRS, and Sputnik-1 are some examples.

NCERT Solutions for Class 8 Science Chapter 17 Stars and The Solar System

October 4, 2019 by Sastry CBSE

Choose the correct answer in Questions 1-3.

Question 1.

Which of the following is NOT a member of the solar system?

(a) An asteroid

(b) A satellite

(c) A constellation

(d) A comet

Answer:

(c) A constellation

NCERT Solutions for Class 8 Science Chapter 17 Stars and The Solar System

October 4, 2019 by Sastry CBSE

NCERT Solutions for Class 8 Science Chapter 17 Stars and The Solar System

Topics and Sub Topics in Class 8 Science Chapter 17 Stars and The Solar System:

Section Name Topic Name

17 Stars and The Solar System

17.1 The Moon

17.2 The Stars

17.3 Constellations

17.4 The Solar System

17.5 Some Other Members of the Solar System

Stars and The Solar System Class 8 Science NCERT Textbook Questions

Choose the correct answer in Questions 1-3.

Question 1.

Which of the following is NOT a member of the solar system?

(a) A satellite

(b) An asteroid

(c) A constellation

(d) A comet

Answer:

(c) A constellation

Question 2.

Which of the following is NOT a planet of the sun?

(a) Sirius

(b) Saturn

(c) Mercury 

(d) Earth

Answer:

(a) Sirius

Question 3: Why do the moon's phases occur? 

(a) We can only view the part of the moon that reflects light in our direction.

(b) the moon's distance from us changes over time.

(c) the Earth's shadow only covers a portion of the moon's surface.

(d) The moon's atmosphere does not have a constant thickness.

Answer: (a) We can only view the part of the moon that reflects light in our direction.

Question 4.

Fill in the blanks.

(a) The planet which is farthest from the Sun is _____

(b) The planet which appears reddish in colour is ______

(c) A group of stars that appear to form a pattern in the sky is known as a _____

(d) A celestial body that revolves around a planet is known as ______

(e) Shooting stars are actually not _____

(f) Asteroids are found between the orbits of and ______

Answer:

(a) Neptune

(b) Mars

(c) constellation

(d) satellite

(e) stars

(f) Mars, Jupiter

Question 5: Is it true (T) or false (F)? 

(a) A member of the solar system is a pole star.

(b) Mercury is the solar system's tiniest planet.

(c) Uranus is the solar system's furthest planet.

(d) INSAT refers to a man-made satellite.

(e) The solar system has nine planets.

(f) Only a telescope is needed to observe the constellation Orion.

Answer:

(a) False

(b) True

(c) False

(d) True

(e) False

(f) False

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