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class 8 Stars and Solar system

Stars and Solar System

  • Universe – the vast space that includes everything on the 🌎 Earth and around it is called Universe.
  • Universe includes celestial or heavenly bodies such as Stars, Planets, Satellites, Meteors Comets, Asteroids.
  • Astronomy the branch of science that deals with the study of heavenly bodies is called Astronomy.
  • People who study about the universe are called Astronomers.
  • Satellite a celestial body revolving around the planet is known as Satellite.
  • All the planets except Mercury and Venus have Natural satellites.
  • Moon is the Earth’s only natural satellite.
  • Moon has no light on its own.
  • The distance of the moon from the Earth is 384,000Km.
  • The time taken by the moon to complete one revolution around the earth is 27 days and 8 hours.
  • Moon’s diameter is 3474 km.
  • Moon surface is made up of mountains and craters.
  • Craters are saucer shaped holes formed when asteroid or a comet hits the surface of the moon.
  • Moon has no air and no atmosphere. So sound cannot travel and we cannot hear.
  • No life exist on the moon due to the absence of atmosphere.
  • Lunar day has a surface temperature -1230 Celsius.
  • Lunar night has a surface temperature -2330 Celsius

We are not able to see the back side of the moon? Why?

  • We never see the back side of the moon from the Earth.
  • This is because moon rotates about its axis in about the same time that it takes to orbit the earth.
  • This result on the same face turned  towards the earth all the times.
  • The side of the moon that faces the earth is called near side, and the opposite side is called far side.

Phases of the Moon:

The day today changes in the shape of the moon as seen from the earth is called as phases of the moon.

There are 6 Phases

1. New moon

2. Waxing crescent moon

3. First quarter

4. Waxing gibbous moon

5. Full moon

6. Waning moon

New Moon:

  • When the moon is in between the Earth and the Sun, then the side of the moon facing the sun is in the opposite direction.
  • The side of the moon facing the earth is dark.
  • This is called as new moon night or amavasya.
  • There is no moonlight during the New moon.

Waxing Crescent Moon:

  • Small sunlit portion seen  on the moon surface is called as crescent moon.
  • The increasing size of the lighted portion of the moon is known as waxing.

First quarter:

  • The sunlit portion of the moon facing the earth becomes bigger.
  • Within a week we can see half of the moon that is called as first quarter.

Waxing Gibbous Moon:

When you are able to see more than half of the moon it is called as Gibbous moon.

Full Moon:

  • The whole sunlit side of the moon is towards the earth during the full moon.
  • Full moon night is called Purnima.
  • It is very bright as you have the maximum moonlight on that day.

Waning Moon:

  • After the full moon sun le portion of the moon facing the earth becomes smaller and smaller. The decreasing size of the lighted part of the moon is called waning.
  • After the full moon during waning we see waning Gibbous moon, third quarter, waning crescent moon and moon complete the revolution around the earth.
  • During a month we see one New moon and one full moon.
  • The time period from one full moon to the next full moon is 29.5 days.
  • And lunar calendar one month is 29.5 days

Stars

Define Stars?

  • Stars are the huge ball of glowing gases held by gravity.
  • Stars consist of hydrogen and helium gas.
  • Heat and light of the star is by nuclear reactions that takes place inside where hydrogen is converted to helium.
  • Stars appear to move from East to West  because the Earth rotates about its Axis from West to East.

Why do sun rise in the East and set in the West??

Earth rotates about its Axis from West to East, so Sun appears to rise in the East and set in the West.

Solar system:

  • It consist of Sun 8 planets their satellites thousands of other heavenly bodies such as asteroids, Meteors, Comets.
  • Sun is the centre of the solar system and all of them revolve around the sun.
  • The sun holds all of them by a gravitational pull.
  • Eight  planets are mercury Venus Earth Mars Jupiter Saturn Uranus and Neptune.

Sun

  • Sun is the nearest star in the solar system.
  • Sun is the glowing ball of gases.
  • Major gases are hydrogen and helium.
  • Nuclear fusion reaction takes place and that releases large amount of energy.
  • Sun is the main source of heat and light of all the objects.
  • Light from the sun reaches the earth 8 minutes 20 seconds.

Characteristic feature of the Sun:

  • The distance of the sun from the earth – 149.60 million km
  • Mass – About 333,000 times heavier than Earth.
  • Size: 109 times bigger than Earth.
  • Diameter – 14 × 10 power 5 Km.
  • Temperature – Surface Temperature – 5500 degree Celsius.
  • Core Temperature -15 million degree Celsius.
  • Life – Sun was formed 4.6 billion years ago. Total life of Sun is 10 billion years.

Planets

  • Planets are the solid heavenly bodies that revolves around the sun in an elliptical orbit.

Difference between Inner planets and Outer planets

Inner planet  Outer Planets  
These are also called as Terrestrial planets.  These are called as a Jovian planets or Gas giants  
Mercury, Venus, Earth Mars are Inner planets  Jupiter Saturn Uranus Neptune are Outer Planets.  
These planets are dense and Rocky surface with no or few moons in it.  This planets have large amount of gases and more moon’s compared to outer planets  

Characteristic features of the Planet:

  1. Planets have no light on its own. They reflect the light from the Sun.
  2. Planets have a definite path in which it revolves around the sun. This path is called orbit.
  3. Time taken by the planet to complete one revolution around the sun is called a period of revolution.
  4. Period of revolution increases as the distance of the planet increases from the Sun.
  5. Period of rotation- time taken by the planet to complete one rotation about it success.
  6. Some planets have one or more natural satellites.

Mercury

  1. The smallest and the nearest planet to the sun.
  2. It takes 88 days to complete one revolution around the sun.
  3. The surface temperature of the Mercury facing the sun 427 degree Celsius and the opposite side is – 173 degree Celsius
  4. It has no satellite
  5. It has negligible atmosphere
  6. It can be seen with the naked eye before the sun rise in the east of sky and after the sunset in the Western sky.

Venus

  1. Venus is the brightest planet.
  2. It is due to the presence of the cloudy atmosphere around it reflect about 3/4th of the sunlight falling on it.
  3. It is closest to the earth and called as Earth’s twin due to the same size of the earth
  4. It is a hot planet.
  5. It has high percentage of carbon dioxide and causes greenhouse effect.
  6. It can be seen with naked eyes.
  7. It has no satellite.
  8. It shows Phases like moon.
  9. In Venus the sun rises in the West and sets in the East because Venus rotates from East to West.
  10. It is called as morning and evening star. Visible for 1 -3 hours before the sun rise in the eastern sky and after sunset in the Western sky.

Earth

  1. Earth is the only planet where life exist.
  2. Earth is at right a distance from the Sun. It has a right temperature, water, atmosphere, and the blanket of ozone.
  3. Earth appears as blue green in colour from the space. It is due to the reflection of the water from the oceans and the land mass on its  surface.
  4. Moon is the natural satellite of the earth.
  5. Axis of rotation is tilted at an angle of 23.5°c to plane of its orbit.
  6. Earth takes 365 half days for rotation around the sun and 24 hours to rotate on its axis.

How rotation causes Day and Night?

  • Earth rotates about honours own axis from West to East
  • The part of the earth that faces the sun move away from it.
  • So rotation causes Day and Night.

Mars

  1. Mars is a red planet. It is due to the presence of the iron oxide in its soil.
  2. It has been atmosphere and traces of Carbon dioxide ,Hydrogen, Nitrogen and Oxygen.
  3. It is colder than Earth.
  4. It has two satellite – Phobos, Deimos.
  5. It can be seen with naked eye.

Jupiter:

  1. It is the largest planet
  2. Mass of Jupiter is about 318 times mass of the earth.
  3. Ganymede is the  largest moon in the solar system.
  4. Jupiter has a thick atmosphere and reflect most of the sunlight and appears bright.
  5. Jupiter has a giant red spot due to the giants from that has been for more years.
  6. It has faint rings around it.

Saturn:

  1. Saturn has rings surrounded due to the eyes and rock particles.
  2. Satellites 82
  3. Yellowish in colour.
  4. It is less dense than water.

Uranus

  1. It also has ring system
  2. It has 27 natural satellites
  3. It rotates from east to west.
  4. Uranus has axis of rotation inclined at 97.8 degrees.

Neptune

  1. It also has ring system
  2. It has 13 satellite.
  3. It as far away from the Sun. It is the coldest planet.
  4. It takes maximum time to revolve around the sun.

Dwarf Planet Pluto

  1. Pluto discovered in 1930.
  2. Average temperature is – 230 degree Celsius
  3. It has five satellite
  4. It takes 248 years to complete one revolution around the sun.
  5. It is  5.9 billion km away from the Sun.
  6. International astronomical union have said that dwarf planets that orbit Sun beyond the Neptune is plutoids.
  7. Eris – a dwarf planet that orbit beyond an Neptune is the plutoid.
  8. Ceres – the main asteroid belt between the mass and Jupiter is also a dwarf planet.

When is Celestial body considered as a Planet??

  • It must orbit around the sun
  • It should have sufficient mass so that it’s gravity can hold it in a spherical shape.
  • It should have clear neighbourhood around its orbit.

Asteroids:

  1. They are small irregular shape heavenly bodies.
  2. They are made up of rocks and metals and revolve around the sun in the gap between orbit of the mass and Jupiter.
  3. They appear as a asteroid belt in this region
  4. Asteroids are pieces of material that are failed to come together to form planets when solar system is formed.
  5. Some say that asteroids are pieces of large planet that went close to Jupiter and break by its gravitational pull
  6. There are 100,000 asteroids.
  7. Asteroids are full of craters indicating that they are because of meteoroids.

Comet

  1. Comet is a small body of ice and dust that revolves around the sun in highly elliptical orbit.
  2. It has a bright head and a long tail.
  3. The tale of the comet always point the sun.
  4. The length of the tile grows as it near the sun.
  5. When comet reach the sun it gets heated up and leaves behind stream of hot glowing gases and dust particles.
  6. Halley comet appear every 76 years. It was last seen in 1986. Next it will be seen in 2061-2062.

Meteoroids:

  1. They are small Rocky irregular heavenly bodies that revolve around the sun.
  2. They do not burn completely on entering the earth atmosphere and lands on the earth surface.
  3. They create large creators and cause lot of damage on earth surface.
  4. It helps the scientist to know about the matter in the outer space.

Meteors

  1. Metors are burning meteoroids they are also called as shooting stars.
  2. It looks like a streak of a straight shooting across the night sky.
  3. Meteors burn completely before they reach the surface of Earth.

One light year if the distance travelled by the light in 1 year.

one Light year = 9.46 × 10 power of 12 Km.

The nearest star to the earth is alpha centauri

It is 40.67 × 10 power 12 Km away from Earth.

Galaxy

  • Large group of stars nebuli and other heavenly bodies bound together by their own gravity is called galaxy.
  • They are the building blocks of universe
  • Each galaxy has 10 to the power of 11 stars
  • Depending on the shape galaxy s can be spiral elliptical or irregular.

Milky way

  • Milky way also called as Akash Ganga
  • It is a spiral galaxy.
  • Sun is the member of the Milky way galaxy.
  • Extent of the milky way is about 100000 light years.

Constellations:

  • The stars that appeared in the form of a close to group and form a recognisable shapes and pattern are known as constellation.
  • Each constellation has been assigned the name, human, animal name or an object.
  • Constellation appear to move in the sky from east to west since Earth rotates from visit to East.
  • Constellation has a group of stars.

Ursa Major

  • It is also called as great dear constellation.
  • It can be seen clearly in the summer season in the Northern part of the sky at the night.
  • It is also known as a great dipper. It has a 7 prominent stars in the form of a dipper (long handled spoon)
  • It is also called as Saptarishi.
  • Ursa Major is also called as a great bear as it resembles the shape of a bear.

Ursa Minor:

  • It is clearly seen in the Northern part of the sky in the July during the summer.
  • It is also called as a little beard little dipper and Laghu Saptarishi.
  • There are 7 prominence stars.
  • At the end of A tale of the Ursa minor is the pole star.

Pole star:

  • Pole star is used to find the directions at the night by the sailors as it always point in the north  direction.
  • Pole star  is not visible in the southern hemisphere.
  • Pole star is also called as polaris or dhuruva Tara.

Orion

  • It is also called as hunter constellation.
  • It is visible during the winter season.
  • It is called as hunter or Mriga or Vyadha.
  • Star Sirius the brightest star in the sky located close to the Orion.

Scorpius:

  • It is visible in July and August.
  • It is known as vrishchika.
  • It has 7 prominent stars and resemble the shape of the scorpion.

Cassiopeia :

  • It is Visible in October than sky.
  • It has seen early to the pole star then called as Sharmishtha.
  • There are 5 stars and they are arranged in the shape of the W or inverted M.

Artificial satellite

  • Artificial satellites are  human made satellites.
  • It is placed in the orbit around the earth or other planets to perform specific function.
  • First artificial satellites Sputnik I launched by USSR on October 4, 1957.
  • The first Indian artificial satellites Aryabhatta launched in 19th April 1975
  • Samatha satellites are INSAT Indian national satellite
  • IRS Indian remote satellite, Kalpana I , EDUSAT

Uses of artificial satellite

  • It is used for forecasting the weather
  • It is used for transmitting the radio on the television signals.
  • It is used for tele communications.
  • It is used for remote sensing for locating the mineral resource underground water for land mapping.
  • It is used for collecting the information about the planets and about the outer space.
  • It is  used for navigation for providing the geographical location of an object on the surface of the earth.
  • GPS Global positioning system
  • Gnss Global navigation satellite system
  • GPS is used for finding the shop hospital land c yar navigation for emergency calls etc.

Our universe is  Expanding

  • Edwin Hubble astronomer ki stated that galaxy  are not stationery they move from each other.
  • The larger the distance between the two galaxy is faster they away from each other.

Big Bang theory

  • According to this theory all the matter in the universe was initially concentrated into the vast mass about 100 million light years.
  • About 15 million years super dense mass exploded.
  • They  flew in all the direction through the space  and lead to the formation of the galaxies

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