Class 7 Unit-11 (The Earth & Space)

 

Unit-11

The Earth & Space

Exercise

 

D. Differentiate between:

  1. Stars and planets
    • Stars have their own light; planets do not have their own light.
    • Stars are hot and glow; planets reflect sunlight.
  2. Inner planets and outer planets
    • Inner planets are closer to the Sun and are rocky (like Mercury, Venus, Earth, Mars).
    • Outer planets are farther and are gaseous (like Jupiter, Saturn, Uranus, Neptune).
  3. Planets and minor planets
    • Planets are large celestial bodies revolving around the Sun in clear orbits.
    • Minor planets (like asteroids) are small and irregular.

E. Give reasons:

  1. The planets nearer to the Sun are hotter than that of farther ones.
    • Because they receive more heat and light from the Sun.
  2. Pluto is not considered a planet.
    • Because it does not clear its orbit and is too small; it is now called a dwarf planet.
  3. Even though many comets and asteroids revolve around the Sun, they are not considered as planets.
    • Because they are too small and have irregular shapes.

F. Very short answer type questions:

  1. What is solar system?
    • The Sun and all celestial bodies (planets, moons, asteroids, etc.) revolving around it.
  2. Which is red planet?
    • Mars.
  3. Which planet was withdrawn from the class of planet?
    • Pluto.
  4. Which planet has the shortest revolution time around the Sun?
    • Mercury.
  5. Which planet is called the twin planet of the Earth?
    • Venus.

G. Short answer type questions:

  1. Why Pluto was withdrawn from the class of planet?
    • Because it is too small and does not clear its orbit; it is now called a dwarf planet.
  2. What is there in the ring of Saturn?
    • Ice, rocks, and dust particles.
  3. What are dwarf planets? Name any three dwarf planets.
    • Small celestial bodies that revolve around the Sun but do not clear their orbit.
    • Examples: Pluto, Ceres, Eris.
  4. Name the largest and smallest planet in solar system.
    • Largest: Jupiter.
    • Smallest: Mercury.

H. Long answer type questions:

  1. What is solar system? How many planets are there in solar system?
    • The solar system consists of the Sun and all celestial bodies revolving around it.
    • There are 8 planets in the solar system.
  2. Write any three significances of the earth.
    • It has life-supporting air and water.
    • It has suitable temperature.
    • It has fertile land for growing food.
  3. Why Pluto was excluded from the class of planets? Which organization is responsible to decide the issues of celestial bodies?
    • Pluto was excluded because it does not clear its orbit and is small.
    • The International Astronomical Union (IAU) is responsible for deciding.

 

 

Next Exercise

 

D. Differentiate between:

1. Full moon and new moon

  • Full moon: The whole face of the moon is fully bright and visible from Earth.
  • New moon: The moon is not visible from Earth because its dark side faces us.

2. Sidereal month and synodic month

  • Sidereal month: Time taken by the moon to complete one revolution around Earth with respect to stars (about 27.3 days).
  • Synodic month: Time taken to complete one cycle of phases (new moon to new moon), about 29.5 days.

3. Bright half and dark half

  • Bright half (Shukla Paksha): Period when the moon is increasing from new moon to full moon.
  • Dark half (Krishna Paksha): Period when the moon is decreasing from full moon to new moon.

4. Waxing Crescent moon and Waning Crescent moon

  • Waxing Crescent: The moon is increasing in brightness after the new moon; a small bright part is seen.
  • Waning Crescent: The moon is decreasing in brightness before the new moon; only a small part remains bright.

5. Waxing Gibbous moon and Waning Gibbous moon

  • Waxing Gibbous: The moon is more than half bright and is increasing towards full moon.
  • Waning Gibbous: The moon is more than half bright but is decreasing after full moon.

 

E. Give reasons

  1. Initial and final position of the moon is not same in one complete revolution.
    → Because Earth also moves around the Sun while the moon revolves around Earth, so the moon’s final position changes.
  2. Moon does not appear on new moon night.
    → Because the side facing Earth does not get sunlight and it cannot be seen.
  3. Moon appears luminous, although it does not emit light.
    → Because it reflects sunlight falling on it.

F. Very short answer type questions

  1. What time does a moon take to revolve around the Earth?
    → About 27.3 days (sidereal month).
  2. What is the surface area of the moon?
    → About 3.8 crore square kilometers (38 million sq. km).
  3. What is the average distance between the moon and the earth?
    → About 3,84,400 km.
  4. What is the time interval of bright half?
    → About 15 days.
  5. How many phases are there in moon cycle?
    → Eight phases.
  6. What is the time difference between sidereal month and synodic month?
    → Sidereal month: 27.3 days, Synodic month: 29.5 days → difference about 2.2 days.

G. Short answer type questions

  1. What is full moon? What is the position of Earth during full moon?
    → When the moon is fully visible from Earth.
    → Earth is between Sun and moon.
  2. How is the phase of the moon changed during bright half?
    → The visible part of the moon increases from new moon to full moon.
  3. How is the phase of the moon changed during dark half?
    → The visible part of the moon decreases from full moon to new moon.
  4. What is sidereal month? What is the period of sidereal month?
    → Time taken by moon to orbit Earth with respect to stars.
    → About 27.3 days.
  5. Which calendar is used in Hindu festivals?
    → Lunar calendar (based on moon phases).

H. Long answer type questions

  1. What is moon? Where is it located?
    → The moon is the natural satellite of Earth.
    → It revolves around Earth at an average distance of 3,84,400 km.
  2. What does lunar month mean? What is its importance?
    → Time taken by moon to complete one full cycle of phases (about 29.5 days).
    → It is important for calendars, Hindu festivals, and tithis.
  3. Differentiate between dark half and bright half.
    • Bright half (Shukla Paksha): From new moon to full moon, moon’s visible part increases.
    • Dark half (Krishna Paksha): From full moon to new moon, moon’s visible part decreases.
  4. Discuss about Adhik maas.
    → An extra lunar month added every 3 years to match lunar calendar with solar year.
    → Called "extra month" or "Purushottam Maas"; considered holy.
  5. Discuss the conditions of sidereal month and synodic month. Which is longer?
    → Sidereal month: 27.3 days, moon revolves around Earth with respect to stars.
    → Synodic month: 29.5 days, moon returns to same phase (new moon to new moon).
    → Synodic month is longer.
  6. What do phases of moon mean? Describe the condition of crescent moon.
    → Phases mean changing shape of visible moon as it orbits Earth.
    → Crescent moon: Less than half of the moon is visible; it appears as a thin curved shape.

 

 

Next Exercise

 

D. Differentiate between

  1. Lunar eclipse and solar eclipse
    • Lunar eclipse: Earth comes between the Sun and Moon; moon is in Earth’s shadow.
    • Solar eclipse: Moon comes between the Sun and Earth; Sun is hidden.
  2. Umbra and penumbra
    • Umbra: Fully dark shadow where light is completely blocked.
    • Penumbra: Partial shadow where light is partly blocked.
  3. Total eclipse and partial eclipse
    • Total eclipse: The whole Sun or Moon is completely covered.
    • Partial eclipse: Only part of the Sun or Moon is covered.

E. Give reasons

  1. Lunar eclipse forms on full moon
    → Because only during full moon, Earth can come between Sun and Moon and block sunlight.
  2. Solar eclipse forms on new moon
    → Because only during new moon, Moon can come between Sun and Earth and block sunlight.

F. Very short answer type questions

  1. Define eclipse.
    → Blocking of light of a celestial body by another body.
  2. What are the basic types of shadow?
    → Umbra and penumbra.
  3. What we call the shadow that does not have any light?
    → Umbra.
  4. What lies in between in lunar eclipse?
    → Earth.
  5. What lies in between in solar eclipse?
    → Moon.

G. Short answer type questions

  1. How is lunar eclipse formed?
    → When Earth comes between Sun and Moon and blocks sunlight to the Moon.
  2. What are the causes of eclipse?
    → When three celestial bodies come in a straight line and one blocks light of another.
  3. How is penumbra formed?
    → When a light source is partly blocked, creating a partial shadow around the dark (umbra) part.
  4. What are the causes of lunar eclipse?
    → Earth’s shadow falls on the Moon when Earth is between Sun and Moon.
  5. What are the causes of solar eclipse?
    → Moon’s shadow falls on Earth when Moon is between Sun and Earth.
  6. How is solar eclipse formed?
    → When Moon comes in front of the Sun and blocks its light from reaching Earth.

 

 

H. Long answer type questions

1. What is shadow? How is it formed?

  • Shadow is a dark area formed when an object blocks light.
  • It is formed when an opaque object comes in the path of light and stops the light from passing behind it.

2. What are the necessary conditions of lunar eclipse? Draw a figure of lunar eclipse.

  • The Moon must be in full moon phase.
  • Earth must come exactly between Sun and Moon.
  • All three (Sun, Earth, and Moon) should be in a straight line.
 

 3. What are the necessary conditions of solar eclipse? Draw a figure of solar eclipse.

  • The Moon must be in new moon phase.
  • Moon should come exactly between Sun and Earth.
  • All three should be in a straight line.

 

 

4. What is eclipse? Why does total lunar eclipse appear long time than that of total solar eclipse?

  • Eclipse is the blocking of light of a celestial body by another body.
  • Total lunar eclipse lasts longer because Earth's shadow is larger than the Moon's shadow on Earth. Also, the Moon moves slowly through the large Earth's shadow.

5. Study the figure and answer:

a. Identify the eclipse, solar or lunar.

  • Solar eclipse.

b. Describe the necessary conditions to form this eclipse.

  • Moon must be in new moon phase.
  • Moon should come between Sun and Earth.
  • All three should be in a straight line.

c. On what day does this eclipse form?

  • On new moon day.

d. What type of eclipse forms if umbra of Moon falls on Earth?

  • Total solar eclipse.

 

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