Chapter 12: Beyond Earth

Bhupendra Rawat -

 

Chapter 12: Beyond Earth


1. Stars and Constellations

  • Stars are huge, very hot objects that produce their own light.
  • Some stars appear bright while others appear dim.
  • A constellation is a defined region of the sky containing a group of stars that appears to form a recognizable pattern.
  • In ancient times, constellations helped travellers and sailors find directions.
  • There are 88 officially recognised constellations, as defined by the International Astronomical Union (IAU).
  • Important constellations mentioned in the chapter:
    • Orion – often imagined as a hunter.
    • Ursa Major – contains the Big Dipper.
    • Ursa Minor – contains the Little Dipper.
    • Canis Major – contains Sirius.
    • Taurus – contains the Pleiades.

2. Pole Star

  • The Pole Star (Polaris/Dhruva Tara) appears nearly stationary in the North direction.
  • It helps us locate the North direction in the Northern Hemisphere.
  • The Big Dipper belongs to Ursa Major.
  • The Little Dipper belongs to Ursa Minor. 

Finding the Pole Star

The two stars at the end of the Big Dipper's cup can be used as pointer stars. An imaginary line through them, extended towards the north by about five times their separation, leads to the Pole Star. 

3. Night Sky Watching

A clear, dark and open place is best for observing stars.

Light Pollution

  • Excessive artificial light at night is called light pollution.
  • Smoke and dust also reduce visibility.
  • Cities generally have more light pollution, so fewer stars are visible.
  • Dark Sky Reserves and parks help preserve dark skies for observation and research. 

Safe Night-Sky Observation

  • Go with an adult to a dark open area.
  • Stay away from bright lights, tall buildings and trees.
  • Choose a suitable date and time using a sky map/app.
  • A moonless, clear night is useful for observing faint objects.
  • Allow your eyes about 30 minutes to adjust to darkness. 

4. The Sun

  • The Sun is a star and is the star closest to Earth.
  • It is a very hot spherical ball of gases.
  • It provides heat and light and is the main source of energy for Earth.
  • Sunlight is essential for plants to grow and therefore supports food chains.
  • The Sun influences climate, seasons, weather, water cycle and winds.
  • The average distance between the Sun and Earth is about 150 million km.
  • This distance is approximately 1 astronomical unit (AU).
  • The Sun is about 100 times larger than Earth in diameter. 

5. Planets

  • A planet is a large, nearly spherical object that revolves around the Sun.
  • Earth takes nearly one year to complete one revolution around the Sun.
  • The eight planets, in order from the Sun, are:

Mercury → Venus → Earth → Mars → Jupiter → Saturn → Uranus → Neptune 

Inner Planets

Mercury, Venus, Earth and Mars

  • Smaller than the outer planets.
  • Have solid, rocky surfaces.

Outer Planets

Jupiter, Saturn, Uranus and Neptune

  • Much larger than Earth.
  • Mostly made of gases and ice.
  • Have ring-like structures made of dust and rocky material. 

6. Interesting Facts About Planets

PlanetImportant Fact
MercuryClosest planet to the Sun
VenusOften called Morning Star or Evening Star
EarthCalled the Blue Planet
MarsCalled the Red Planet
JupiterLargest planet
SaturnFamous for its prominent rings
UranusOuter giant planet
NeptuneFarthest of the eight planets from the Sun
  • Venus is the brightest planet visible in the sky.
  • Mars looks red because its soil is reddish.
  • Earth appears blue from space because much of its surface is covered with water.
  • Pluto is a dwarf planet, not one of the eight planets. 

7. Planets and Stars – How Are They Different?

  • Stars produce their own light.
  • Planets do not produce their own light; they are visible because they reflect sunlight.
  • Stars generally appear to twinkle.
  • Planets usually appear as steadier points of light.
  • Some planets, such as Venus, Mercury, Mars, Jupiter and Saturn, can be seen with the naked eye under suitable conditions. 

8. Satellites and the Moon

  • Objects that move around planets are called satellites.
  • A planet's naturally occurring satellite is called a natural satellite or moon.
  • Earth has one Moon.
  • Mars has two moons.
  • Some outer planets have many moons.

The Moon

  • The Moon is Earth's natural satellite.
  • It takes about 27 days to complete one revolution around Earth.
  • It is Earth's nearest neighbour in space.
  • The Moon has very little atmosphere.
  • Its diameter is about one-fourth that of Earth.
  • The Moon's surface has bowl-shaped structures called craters.
  • Many craters were formed by impacts of asteroids or other space rocks.
  • The Moon is about 3,84,000 km from Earth. 

9. India's Chandrayaan Missions

  • Chandrayaan-1 – launched in 2008.
  • Chandrayaan-2 – launched in 2019.
  • Chandrayaan-3 – launched in July 2023.
  • Chandrayaan-3's Vikram lander successfully soft-landed near the Moon's south pole on 23 August 2023.
  • India became the first country to achieve a landing near the Moon's south pole.
  • 23 August is celebrated in India as National Space Day.
  • Chandrayaan-4 is being planned to bring back lunar soil and rock samples. 

10. Asteroids

  • Asteroids are small, rocky and irregularly shaped objects in the Solar System.
  • Many asteroids revolve around the Sun between the orbits of Mars and Jupiter.
  • This region is called the asteroid belt.
  • Some asteroids can pass close to Earth. 

11. Comets

  • Comets are objects made mainly of dust, gases, rocks and ice.
  • They come from the outer regions of the Solar System.
  • They may develop a long tail when they approach the Sun.
  • The frozen material begins to evaporate near the Sun, helping form the tail.
  • Halley's Comet appears approximately every 76 years. 

12. Solar System

The Solar System consists of:

  • The Sun
  • Eight planets
  • Their moons
  • Asteroids
  • Comets
  • Other smaller objects

The Sun is the largest and heaviest object in the Solar System and produces almost all its energy. Other objects are visible mainly because they reflect sunlight. 

13. Milky Way Galaxy

  • Our Solar System is part of the Milky Way Galaxy, also called Ākāśa Gaṅgā.
  • A galaxy contains millions to billions of stars.
  • From a dark location, the Milky Way can appear as a faint band of light across the night sky. 

14. The Universe

  • The Milky Way is only one galaxy among many galaxies in space.
  • The vast collection of galaxies, stars, planets and other matter and space is called the Universe.
  • Scientists continue to study the Universe and search for answers about life beyond Earth.
  • Scientists have not yet found evidence of life elsewhere in the Universe.
  • The search especially includes exoplanets, which are planets revolving around stars other than our Sun. 

Quick Revision Points

  1. Sun → a star
  2. Earth → a planet
  3. Moon → Earth's natural satellite
  4. Pole Star → helps locate North
  5. Big Dipper → Ursa Major
  6. Little Dipper → Ursa Minor
  7. Orion → constellation
  8. Sirius → brightest star in the night sky
  9. Venus → Morning/Evening Star
  10. Mars → Red Planet
  11. Earth → Blue Planet
  12. Eight planets → Mercury to Neptune
  13. Pluto → dwarf planet
  14. Asteroids → rocky objects; many lie between Mars and Jupiter
  15. Comets → icy, rocky objects that may develop tails
  16. Solar System → part of Milky Way
  17. Milky Way → our home galaxy
  18. Universe → contains many galaxies
  19. 23 August → National Space Day in India
  20. Light pollution → excessive artificial light at night
NCERT QUESTIONS/ANSWERS

1. Match the Column

  • (i) Satellite of Earth  (d) Moon

  • (ii) Red planet  (c) Mars

  • (iii) Constellation  (a) Orion

  • (iv) Planet which is commonly called an evening star  (b) Venus

2. Riddles

(i) Solve the riddle:

  • 1st letter: in MAN, not in CAN -  M

  • 2nd letter: in ACE and FAN - A

  • 3rd letter: in RAT, not in CAT - R

  • 4th letter: in SUN, not in FUN - S

Answer: MARS

(ii) Two similar riddles:

Riddle 1:

  • My first letter is in SUN, but not in RUN.

  • My second letter is in CAT, and also in RAT.

  • My third letter is in TOP, but not in POP.

  • My fourth letter is in SUN, and also in RUN.

  • My fifth letter is in RED, and also in BED.

  • My sixth letter is in NET, but not in PET.

  • What am I?

    • Answer: SATURN

Riddle 2:

  • My first letter is in EAT, but not in CAT.

  • My second letter is in ART, and also in RAT.

  • My third letter is in RED, but not in BED.

  • My fourth letter is in TAP, and also in MAP.

  • My fifth letter is in HAT, but not in CAT.

  • What am I?

    • Answer: EARTH

3. Which of the following is not a member of our Solar System?

(i) Sirius

(Note: Sirius is a star located outside our Solar System, whereas asteroids, comets, and dwarf planets like Pluto are part of it).

4. Which of the following is not a planet of the Sun?

(ii) Pluto

(Note: Pluto was reclassified as a dwarf planet in 2006).

5. Which is the brighter star, the Pole Star or Sirius?

Sirius is much brighter than the Pole Star. In fact, Sirius is the brightest star visible in the night sky.

6. Order of the planets from the Sun

The standard order of the planets starting from closest to the Sun outward is:

  1. Mercury

  2. Venus

  3. Earth

  4. Mars

  5. Jupiter

  6. Saturn

  7. Uranus

  8. Neptune

7. Identifying patterns in the sky (Big Dipper, Little Dipper, Pole Star)

  • Big Dipper (Saptarishi): Connect the 7 brightest stars that form a bowl with a handle (resembling a large ladle).

  • Pole Star (Dhruva Tara): Locate the two "pointer stars" at the end of the Big Dipper’s bowl. Imagine a straight line extended through them toward the north—it points directly to the Pole Star.

  • Little Dipper: The Pole Star is the star at the very tip of the handle of the Little Dipper.

8. Identifying Orion and Sirius

  • Orion: Connect the stars forming the central "Belt" (3 bright stars in a line), surrounded by four outer stars forming a quadrilateral body (representing a hunter).

  • Sirius: Follow the line formed by the three belt stars of Orion downward/southeastward. The bright star that line leads to is Sirius.

9. Why do stars disappear during the day?

During the day, the Sun shines extremely brightly. Its intense glare scatters throughout the Earth's atmosphere, overwhelming the faint light coming from distant stars and making them invisible to us.

10. Observation of the Big Dipper over time

  • Does it appear to move? Yes.

  • Explanation: As the Earth rotates on its axis from west to east during the night, the Big Dipper appears to revolve slowly around the Pole Star in a counter-clockwise direction. The Pole Star itself remains in a fixed position in the northern sky.

11. Poem on the Night Sky

The Night Canopy

When the glowing Sun goes down to sleep,

Out from the darkness the bright stars peep.

Silver beams on a canvas of night,

A thousand distant suns burning bright.

The Big Dipper traces its gentle arc,

Guiding the travelers through the dark.

And standing constant, calm and clear,

The Pole Star whispers, "I am here."


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