Grade 7 Q&A: Chapter 20: In the World of Stars

Concept Questions

Q1: What is a star?

Answer: A star is a massive, luminous ball of plasma (hot, ionized gas) held together by its own gravity. It produces light and heat through nuclear fusion reactions in its core, where hydrogen atoms fuse to form helium.

Q2: Why do stars twinkle?

Answer: Stars twinkle because of the Earth's atmosphere. As starlight passes through different layers of the atmosphere, which have varying temperatures and densities, it gets refracted (bent) multiple times. This rapid and random bending of light causes the star's apparent brightness and position to fluctuate, making it appear to twinkle.

Q3: What is a light-year?

Answer: A light-year is a unit of distance used to measure the vast distances in space. It is defined as the distance that light travels in one year. Since light travels at approximately 300,000 kilometers per second, a light-year is an incredibly large distance.

Q4: What is a constellation?

Answer: A constellation is a group of stars that appear to form a recognizable pattern or shape in the night sky as seen from Earth. These patterns are imaginary and were created by ancient civilizations for navigation, timekeeping, and cultural storytelling.

Q5: Name any five constellations.

Answer: Five examples of constellations are:

• Ursa Major (The Great Bear / Saptarishi)
• Ursa Minor (The Little Bear / Dhruva Matsya)
• Orion (The Hunter)
• Leo (The Lion)
• Scorpius (The Scorpion)

Q6: What is the Pole Star?

Answer: The Pole Star, also known as Polaris, is a star that appears almost stationary in the night sky and is located very close to the North Celestial Pole. It is particularly important for navigation in the Northern Hemisphere because it always points towards the North direction.

Q7: What is the Solar System?

Answer: The Solar System is the gravitationally bound system of the Sun and all the objects that orbit it, either directly or indirectly. It includes the eight planets, dwarf planets, moons, asteroids, comets, and interplanetary dust and gas.

Q8: What are artificial satellites? Give their uses.

Answer: Artificial satellites are man-made objects that are launched into space and orbit the Earth or other celestial bodies.
Their uses include:

• Communication (e.g., telephone, internet, television)
• Weather forecasting
• Remote sensing (e.g., Earth observation, agriculture monitoring)
• Navigation (e.g., GPS)
• Scientific research (e.g., astronomy, space exploration)

Exercise Solutions (from Page 130)

1. Fill in the blanks.

a. Stars twinkle due to the Earth's atmosphere.

b. The distance of the stars is measured in light-years.

c. The nearest star to the Earth is the Sun.

d. The Pole Star is also called Polaris.

e. The Sun and the planets constitute the Solar System.

2. Write true or false.

a. The Sun is a planet. False (The Sun is a star.)

b. The stars in a constellation are at the same distance. False (They only appear to be close from our perspective.)

c. The Pole Star appears to be stationary. True

d. The distance between the Earth and the Sun is measured in light-years. False (It's measured in Astronomical Units (AU).)

e. Aryabhata is an artificial satellite. True

3. Match the following.

a. The Sun - Star

b. Ursa Major - Constellation

c. Light-year - Unit of distance

d. Pole Star - Polaris

e. Artificial satellite - Man-made

4. Answer in one word.

a. What is the distance of the stars measured in? Light-years

b. What is the name of our galaxy? Milky Way

c. What is the name of the nearest star to the Sun? Proxima Centauri

d. What is the name of the Pole Star? Polaris

e. What is the name of the first artificial satellite? Sputnik 1

5. Answer the following questions.

a. What are stars?

Answer: Stars are massive, self-luminous celestial bodies made up of gases, primarily hydrogen and helium. They generate light and heat through nuclear fusion reactions in their cores.

b. Why do stars twinkle?

Answer: Stars twinkle due to the refraction (bending) of starlight as it passes through the Earth's turbulent atmosphere. Different layers of air have varying temperatures and densities, causing the light to bend in different directions, resulting in the apparent twinkling effect.

c. What is a constellation? Give two examples.

Answer: A constellation is a group of stars that form a recognizable pattern or figure in the sky, as seen from Earth.
Examples:

• Ursa Major (The Great Bear)
• Orion (The Hunter)

d. Write a short note on the Pole Star.

Answer: The Pole Star, or Polaris, is a star located very close to the North Celestial Pole. It appears stationary in the sky and is used for navigation in the Northern Hemisphere because it indicates the direction of North. It is part of the constellation Ursa Minor (The Little Bear).

e. What is the Solar System? Name the planets in it.

Answer: The Solar System is the system of planets and other celestial objects that orbit the Sun.
The planets in our Solar System, in order from the Sun, are:

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

f. Write the uses of artificial satellites.

Answer: Artificial satellites have various uses, including:

• Communication (telephone, internet, television)
• Weather forecasting
• Remote sensing (Earth observation, resource monitoring)
• Navigation (GPS)
• Scientific research (space exploration, astronomy)

Application Questions

Q1: Imagine you are lost at night in a forest. How would you use the Pole Star to find your way?

Answer: If I were lost in a forest at night, I would first try to locate the constellation Ursa Major (The Great Bear or Saptarishi). It looks like a big dipper. I would then identify the two stars at the end of the dipper's bowl, known as the "pointer stars." By drawing an imaginary line extending from these pointer stars, I could locate the Pole Star (Polaris). Since the Pole Star is always in the North direction, I could use it as a reference to determine North and orient myself to find my way out of the forest.

Q2: Why do we see different constellations at different times of the year?

Answer: We see different constellations at different times of the year because of the Earth's orbit around the Sun. As the Earth moves along its orbit, our night sky faces different directions in space. This means that we are looking at different sets of stars at different points in our orbit. Some constellations are visible in the Northern Hemisphere's summer, while others are visible in winter, spring, or autumn.

Q3: Explain why it is important to study artificial satellites.

Answer: Studying artificial satellites is important for several reasons:

• Technological Advancement: It drives innovation in various fields like communication, materials science, and electronics.
• Understanding Earth: Satellites provide crucial data for studying Earth's climate, weather patterns, oceans, and land resources.
• Navigation and Communication: They enable global communication and navigation systems that are essential for everyday life and transportation.
• Disaster Management: Satellites help in monitoring and managing natural disasters, providing timely information for relief efforts.
• Space Exploration: They are vital tools for exploring the universe, studying distant stars and galaxies, and understanding our place in the cosmos.