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Stars And The Solar System Class 8 Notes - Chapter 17 Notes



On this page, you will find notes, questions, and answers to class 8 science chapter 17 Stars and The Solar System. These notes, explanations, examples, and questions and answers are according to CBSE and the NCERT textbook. If you like the study material, feel free to share the link as much as possible.

Stars and the Solar System

  • All the objects in the sky (the sun, stars, planets, the moon, and other objects) are called celestial objects.
  • The sun and its solar system are part of a huge cluster of billions of stars referred to as a galaxy.
  • The galaxy to which we belong is the Milky Way galaxy. The name given to this galaxy is because it appears as a milk split across the sky.
  • The study of celestial objects and associated phenomena is called astronomy.
  • The Moon is the celestial body closest to us.
  • Celestial bodies are separated from each other by very large distances. So these large distances are measured in units of light-years. 1 light-year is the distance covered by light in one year.

Stars

  • Stars are luminous, heavenly, celestial objects or bodies that emit heat and light of their own as they are very hot.
  • Sun is our nearest star and the nearest star next to Sun is Alpha Centauri.
  • Stars are held together by gravity. Stars are also present in the sky during the daytime but are not visible to us due to the bright light of the sun.
  • Sirius is the brightest star in the sky.
  • The stars appear to be moving from east to west.

  • The Pole star, also called Dhruvtara, appears stationary from the earth as it is situated in the direction of the earth's axis. It is also known as a stationary star. This makes the pole star useful for navigation purposes. That’s why stars are important.

What is special about Pole Star?

Pole stars appear stationary from any location on the planet. This is due to its location along the earth's axis of rotation. In the north, the pole star is located above the Earth.

Why do stars seem to twinkle?

Because of their large distance from the Earth and atmospheric disturbances, the stars appear to sparkle. It takes years for light from the stars to reach Earth.

The distance between Alpha Centauri (the next closest star after the sun) and the earth is approximately 40,000 billion kilometers, implying that stars are further distant from the planet than the sun.

The Sun

  • The sun is both a celestial body and a star, emitting its own light.
  • It is the main source of light and energy for all the planets of the Solar system.
  • It is the closest star and the center of our solar system.
  • Now the question arises, why do stars look small to us and the sun look bigger as if they are both stars?
  • The stars look small to us as they are far from us and, from a long-distance, they appear as small dots and the sun looks bigger as the sun is closest to the earth.

The distance between the Sun and Earth

The distance from the sun to the earth is approximately 150,000,000km or 150 million km.

Constellations

A group of stars form a recognizable shape or pattern in the sky and are usually named after mythological characters, people, animals, and objects. There are 88 known constellations, of which only a few, like Ursa Major, Ursa Minor, Orion, Cassiopeia, and Leo Major can be identified with the naked eye.

Ursa Major

  • This constellation is also known as Saptrishi in Hindi as it consists of seven prominent stars.
  • This constellation is also referred to as the Big Dipper as they are arranged in the shape of a big dipper.
  • This constellation is also referred to as the Great Bear, as the seven stars, along with less prominent stars, form the outline of a big bear.

Ursa Major and Ursa minor constellations (clip source canva.com)

Ursa Minor

  • This constellation is also known as the Little Dipper and consists of seven stars.
  • This constellation is also known as the Little Dipper.

Cassiopeia

Cassiopeia Constellation
Cassiopeia Constellation (source canva.com)
  • It is a constellation that can be seen in the Northern sky.
  • It resembles the shape of a W or M.

Orion

Orion Constellation
Orion Constellation (Source Canva.com)
  • A major constellation that is visible throughout the world.
  • Orion helps in locating Sirius, the brightest star in the sky.
  • The shape of Orion resembles that of a hunter as the eight bright stars make that pattern.
  • The three central stars depict the hunter's belt. The four bright stars resemble a quadrilateral.

Moon

The Moon revolves around the earth and doesn’t have its own light. It reflects the light of the sun. That's why we are able to see the moon.

The surface of the moon

  • The surface of the moon has many craters of different sizes and also a large number of steep and high mountains.
  • Life is not possible on the Moon as there is an absence of air and water.
  • Neil Armstrong was the first man to land on the Moon, followed by Edwin Aldrin.

Phases of the Moon

Phases of Moon
  • We always see the same side of the Moon because the Moon completes one rotation on its axis at the same time as it takes to complete one revolution around the earth.
  • Phases of the Moon can be defined as the different shapes or appearance of the visible part of the Moon as seen from the Earth.
  • The phases of the moon occur due to its continuously changing positions with respect to the Earth and the Sun.

The solar system


Solar System (clip source canva.com)
  • The sun and its eight planets, along with comets, asteroids, and meteors which revolve around the sun, form the solar system.
  • The sun is also a star and is closest to earth.
  • The sun is at the center of our solar system.
  • The sun emits heat and light. So it is a major source of heat and light for all the planets in the solar system.
  • The constellation is not a member of the solar system.

Planets

  • A celestial body that moves around the sun.
  • Planets are smaller than stars and don’t have light of their own like stars.
  • The stars twinkle whereas the planets do not, making it simple to identify planets in the night sky.
  • Planets reflect the sunlight that falls on them.
  • The planet has a definite path in which it revolves around the sun, and this path is known as orbit. It is important to note here that planets orbit around the sun in elliptical orbits.
  • The period of revolution of each planet rises as the distance between the sun and the planets increases.
  • Planets are different from other objects, such as comets, asteroids, and meteors.
  • Some planets have their own satellites.
  • The Moon is a natural satellite that revolves around the earth in just the same way the earth revolves around the sun.

There are eight planets in our solar system.

  1. Mercury
  2. Venus
  3. Earth
  4. Mars
  5. Jupiter
  6. Saturn
  7. Uranus
  8. Neptune

The first four planets, such as Mercury, Venus, Earth, and Mars, are much nearer to the Sun and are called the inner planets. The inner planets are also known as terrestrial planets. The inner planets have very few moons.

The planets outside the orbit of Mars, namely Jupiter, Saturn, Uranus, and Neptune, are much farther off than the inner planets and are called the outer planets. The outer planets have a large number of moons.

Mercury-(Budh)

  • It is the smallest planet in our solar system as it is the nearest planet to the sun.
  • It has no satellite of its own.
  • Mercury is a rocky planet that has a solid surface covered with craters.
  • Life could not be possible on this planet due to extreme temperature variations and it has no atmosphere.

Venus (Shukra)

  • Brightest planet in the night sky.
  • Because of its close proximity to the sun, Venus is the hottest planet.
  • It is often called the morning or evening star.
  • Venus has no satellite of its own.
  • Venus rotates from east to west, whereas the Earth rotates from west to east.

Earth (Prithvi)

  • The planet on which we live.
  • The earth is the only planet on which we live.
  • The earth appears blue-green due to the reflection of light from water and landmass on its surface.
  • The earth has its own satellite called the Moon, which revolves around it.

Mars (Mangal)

  • It is also called the red planet.
  • It has two small natural satellites.
  • Life is not possible on this planet due to the availability of oxygen (0.16%)

Jupiter (Brihaspati)

  • It is the largest planet in our solar system.
  • The mass of Jupiter is about 318 times that of our Earth.
  • It has a large number of satellites.
  • It has faint rings around it.

Saturn (Shani)

  • It appears yellowish in color.
  • Saturn has beautiful rings around it.
  • These rings are not visible to the naked eye.
  • Saturn also has a large number of satellites.

Uranus and Neptune

  • The outermost planet of the solar system, which can be seen only with the help of telescopes.
  • Uranus also rotates from east to west.
  • Neptune is the farthest planet from the sun.
  • Neptune has 8 natural satellites of its own.

Asteroids

Small objects which revolve around the sun and are found in between the orbits of Mars and Jupiter. It can only be seen through large telescopes.

Comets

A comet appears generally as a bright head and a glowing gaseous outer cloud called the coma. The comet revolves around the earth and when it reaches the sun, the coma spreads out in the form of a long tail.

Meteors and Meteorites

A bright streak of light in the sky is commonly known as a shooting star. A small object that occasionally enters the earth’s atmosphere.

Meteorites

The small rocky pieces revolve around the sun. When a piece of the meteoroid survives the trip to earth and lands on earth, they are called meteoroids.

How do the days and nights occur?

Day and night occur due to the rotation of the earth. The Earth rotates on its own axis. It takes 24 hours to complete one rotation.

Satellites

A celestial object that revolves around a planet.

Satellites are divided into two categories.

  1. Natural satellite-The Moon is the natural satellite of the Earth.
  2. Artificial satellite – Satellites that are made by man and are placed in orbit around the Earth with the help of a rocket.

The artificial satellites which are man-made objects are much nearer to the Earth than its natural satellite.

Artificial satellites are used for a variety of purposes, including weather forecasting, the transmission of television and radio broadcasts, telecommunication, and remote sensing. Several artificial satellites have been created and launched by India.

The first artificial satellite launched by India was Aryabhatta in 1975.

Questions and Answers

Why are stars invisible during the daytime?

During the day and at night stars are present in the sky. During the day, however, the sunshine is so strong that it is difficult to see stars in the sky.

Why do stars appear moving from east to west?

The Earth spins in a west-to-east direction. The earth appears to be still to us, while the sky appears to be moving east to west. It is not, however, correct. The sun appears to rise in the east and set in the west for the same reason.

Can stars change their positions?

After observing a star or group of stars for a few hours, their location appears to change. This is due to the earth's motion. The earth is constantly revolving around the sun, thereby changing its position relative to the stars.

What is a lunar eclipse?

The lunar eclipse happens when the moon, Earth, and Sun are all very close to each other, with the Earth directly in the midst of the moon and the sun. As a result, the earth's shadow falls on the moon.

Thus, during a lunar eclipse, the moon does not reflect sunlight but rather the light it gets from the earth. During a lunar eclipse, the moon appears to be reddish in color.

What is the Moon Cycle?

The cycle is about 29 days, where it goes from a full moon to a new moon to a full moon.

What is Astronomy?

Astronomy is a branch of science that studies celestial bodies and their associated phenomena.

What are the different types of lunar phases?

Various shapes of the bright part of the moon seen during a month are known as the phases of the moon.

What is 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.

What is the difference between a star and a constellation?

Stars are one of the celestial bodies which emit light of their own whereas Constellations are the group of stars that appear to form some recognizable shape or pattern is known as a constellation.

What is a satellite?

Any celestial body revolving around another celestial body is called its satellite.

What is the temperature of the moon?

If we talk about the temperature of the moon during the daytime it is 100 degrees Celsius and at night it is 168 degrees Celsius because of such inhabitable conditions.

What is the Full Moon Day?

The Full Moon day is when the whole disc of the moon facing towards the earth is visible to us.

What is the constellation of Big Dipper?

Ursa Major One of the most famous constellations which you can see during summertime, in the early part of the night. The seven big bright stars comprise this constellation. These stars resemble the form of a large interrogatory mark or a ladle. The ladle handle is done by connecting the 3 stars into a row, with the four other stars in the shape of the ladle's bowl.

Where is Sirius?

Sirius is the brightest star in the sky and it is located close to Orion.



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