GSEB Class 8 Science Solutions Chapter 17 Stars and The Solar System

Question 1. Which of the following is NOT a member of the solar system?
(a) An asteroid
(b) A satellite
(c) A constellation
(d) A comet.
Answer: (c) A constellation
In simple words: Constellations are just patterns we see in stars, not actual objects in our solar system.

Exam Tip: Remember the difference between objects *in* the solar system (planets, asteroids, comets, satellites) and objects or patterns *observed from* Earth (stars, constellations).

Question 2. Which of the following is NOT a planet of the sun?
(a) Mercury
(b) Saturn
(c) Earth
(d) Sirius
Answer: (d) Sirius
In simple words: Sirius is a star, not a planet orbiting our Sun.

Exam Tip: Always distinguish between stars, planets, and other celestial bodies based on their characteristics and orbital paths.

Question 3. Phases of the moon occur because:
(a) we can see only that part of the moon which reflects light towards us.
(b) our distance from the moon keeps changing.
(c) the shadow of the earth covers only a part of the moon's surface.
(d) the thickness of the moon's atmosphere is not constant.
Answer: (a) We can see only that part of the moon which reflects light towards us.
In simple words: Moon phases occur because we see different amounts of its sunlit part as it moves around Earth.

Exam Tip: Understand that lunar phases are due to the changing geometry of the Sun-Earth-Moon system, not Earth's shadow (that causes eclipses) or distance variations.

Question 4. Fill in the blanks:
(a) The planet which is farthest from the Sun is __________.
(b) The planet which appears reddish in color is __________.
(c) A group of stars that appear to form a pattern in the sky is known as a __________.
(d) A celestial body that revolves around a planet is known as __________.
(e) Shooting stars are not __________.
(f) Asteroids are found between the orbits of __________ and __________.
Answer:
(a) The planet that is furthest from the Sun is **Neptune**.
(b) The planet that looks reddish in color is **Mars**.
(c) A group of stars that forms a recognizable shape in the sky is called a **Constellation**.
(d) A celestial body that orbits a planet is known as a **Satellite**.
(e) Shooting stars are not **meteors**. (They are just small pieces of rock burning up in the atmosphere, not actual stars.)
(f) Asteroids are found between the orbits of **Mars** and **Jupiter**.
In simple words: The solar system has many distinct features like the farthest planet, colorful planets, star groups, and objects orbiting planets, and asteroids exist between Mars and Jupiter.

Exam Tip: Be precise with terminology for celestial objects; for instance, "shooting stars" are meteors, not stars, and constellations are patterns, not single bodies.

Question 5. Mark the following statements is true or false:
(a) Pole star is a member of the solar system.
(b) The smallest planet of the solar system is Mercury.
(c) Uranus is the farthest planet in the solar system.
(d) INSAT is an artificial satellite.
(e) There are nine planets in the solar system.
(f) Constellation Orion can be seen only with a telescope.
Answer:
(a) The Pole star is a member of the solar system. **False**. (The Pole star is a distant star, not part of our solar system.)
(b) The smallest planet of the solar system is Mercury. **True**. (Mercury is indeed the smallest planet in our solar system.)
(c) Uranus is the farthest planet in the solar system. **False**. (Neptune is the farthest known planet from the Sun.)
(d) INSAT is an artificial satellite. **True**. (INSAT refers to a series of Indian geostationary communication and meteorological satellites.)
(e) There are nine planets in the solar system. **False**. (There are now eight recognized planets; Pluto is considered a dwarf planet.)
(f) Constellation Orion can be seen only with a telescope. **False**. (Orion is a prominent constellation easily visible to the naked eye.)
In simple words: Know whether statements about stars, planets, and satellites are right or wrong by understanding basic astronomy facts.

Exam Tip: Review key facts about the solar system, stars, and satellites, especially common misconceptions about the number of planets or visibility of constellations.

Question 7. In which part of the sky can you find Venus, if it is visible as an evening star?
Answer: If Venus is visible as an evening star, you can find it in the western part of the sky just after sunset.
In simple words: When Venus appears as an evening star, look for it in the west after the sun goes down.

Exam Tip: Remember that "evening star" or "morning star" refers to planets like Venus that are visible low in the sky just after sunset or before sunrise, always appearing near the Sun's path.

Question 8. Name the largest planet of the solar system.
Answer: Jupiter is the largest planet within our solar system. It is significantly larger than all the other planets combined.
In simple words: Jupiter holds the title for the biggest planet in our solar system.

Exam Tip: Basic facts about planets, like their size order, are important to remember for quick recall questions.

Question 9. What is a constellation? Name any two constellations.
Answer: A constellation is a collection of stars that appear to form a specific, recognizable pattern or shape when viewed from Earth. Two common constellations are the Great Bear (Ursa Major) and Orion.
In simple words: Constellations are groups of stars that seem to make pictures in the sky, like the Great Bear and Orion.

Exam Tip: When defining constellations, emphasize that the stars *appear* grouped from Earth, but are often far apart in space. Always give examples.

Question 10. Draw sketches to show the relative positions of prominent stars in
(a) Ursa Major
(b) Orion.
Answer:
For **Ursa Major** (the Great Bear or Big Dipper), the sketch should show seven bright stars forming a ladle shape. Four stars make the bowl, and three make the handle. The two stars at the end of the bowl, called the "Pointers," point towards Polaris (the Pole Star).
For **Orion** (the Hunter), the sketch should depict a prominent pattern of bright stars, including three stars in a row that form Orion's Belt. Above and below the belt are other bright stars representing his shoulders and feet, such as Betelgeuse (red giant) and Rigel (blue supergiant).
In simple words: For Ursa Major, draw the Big Dipper shape. For Orion, show the three-star belt and other bright stars around it, forming a hunter shape.

Exam Tip: When drawing constellations, focus on the distinct star patterns and their relative brightness to make them easily recognizable. Label the key stars if possible.

Question 11. Name two objects other than planets which are members of the solar system.
Answer: Two celestial objects besides planets that are part of the solar system are **comets** and **asteroids**. These objects orbit the Sun, just like planets do.
In simple words: Other things in our solar system besides planets include comets and asteroids.

Exam Tip: Remember to include dwarf planets, moons, and meteors as other non-planet solar system members if asked for more examples.

Question 12. Explain how you can locate the Pole star with the help of Ursa Major.
Answer: You can find the Pole Star using the Ursa Major constellation (also known as the Big Dipper). First, locate the two "pointer" stars at the outer edge of the Big Dipper's bowl. Next, draw an imaginary straight line through these two stars and extend it upwards. Follow this imaginary line for roughly five times the distance between the two pointer stars, and you will arrive at a moderately bright star, which is the Pole Star. This star always appears in the north direction.
In simple words: To find the Pole Star, use the two end stars of the Big Dipper's bowl. Draw an imaginary line through them and extend it about five times their distance; that's the Pole Star.

Exam Tip: Practice identifying constellations and key stars. Knowing how to find the Pole Star is a fundamental sky navigation skill.

Question 13. Do all the stars in the sky move? Explain.
Answer: No, not all stars in the sky appear to move in the same way. Most stars seem to drift from east to west across the night sky. This apparent movement happens because of the Earth's own rotation on its axis from west to east. However, the Pole Star (Polaris) remains almost stationary in the sky, appearing not to move at all, as it is nearly aligned with Earth's axis of rotation.
In simple words: Most stars look like they move because Earth spins. The Pole Star stays in one spot because it's directly above Earth's axis.

Exam Tip: Differentiate between the apparent motion of most stars (due to Earth's rotation) and the stationary nature of the Pole Star (due to its alignment with the Earth's rotational axis).

Question 14. Why is the distance between stars expressed in light years? What do you understand by the statement that a star is eight light-years away from the earth?
Answer: Distances between stars are immense, often spanning millions or trillions of kilometers. For example, the distance from the Sun to Earth is 150,000,000 km, but Alpha Centauri is approximately 40,000,000,000,000 km away. Using such large numbers in kilometers becomes impractical for astronomical measurements. Therefore, distances in space are typically expressed in light-years. A light-year represents the total distance that light travels in one Earth year. So, if a star is eight light-years away from Earth, it signifies that the light from that star takes eight years to reach our planet.
In simple words: Star distances are so huge that kilometers are too big to use. A light-year is how far light travels in one year. Eight light-years means light takes eight years to get here from that star.

Exam Tip: Clearly define a light-year as a unit of *distance*, not time. Emphasize why it's a practical unit for astronomical scales.

Question 15. The radius of Jupiter is 11 times the radius of the Earth. Calculate the ratio of the volumes of Jupiter and the Earth. How many Earths can Jupiter accommodate?
Answer: To calculate the ratio of their volumes, let's start by defining Earth's radius.
Let the radius of the Earth be \( R \) units.
The volume of the Earth is given by the formula for a sphere: \( V_{Earth} = \frac {4}{3} \pi R^3 \) cubic units.
Since the radius of Jupiter is 11 times the radius of Earth, the radius of Jupiter will be \( 11R \) units.
The volume of Jupiter is \( V_{Jupiter} = \frac {4}{3} \pi (11R)^3 \).
Expanding this, \( V_{Jupiter} = \frac {4}{3} \pi (1331R^3) \) cubic units.
Now, to find the ratio of the volume of Jupiter to the volume of Earth:
\( \frac {V_{Jupiter}}{V_{Earth}} = \frac { \frac {4}{3} \pi (1331R^3) }{ \frac {4}{3} \pi R^3 } \)
The \( \frac {4}{3} \pi \) and \( R^3 \) terms cancel out, leaving:
\( \frac {V_{Jupiter}}{V_{Earth}} = \frac {1331}{1} \)
\( \implies \) The ratio of the volumes of Jupiter and Earth is \( 1331 : 1 \).
\( \implies \) Therefore, Jupiter can accommodate 1331 Earths within its volume.
In simple words: If Jupiter's radius is 11 times Earth's, its volume is 1331 times larger. This means Jupiter is big enough to fit 1331 Earths inside it.

Exam Tip: Remember the formula for the volume of a sphere (\( V = \frac{4}{3} \pi r^3 \)) and how scaling the radius affects the volume (e.g., if radius is \( x \) times larger, volume is \( x^3 \) times larger).

Question 16. Boojho made the following sketch of the solar system (Fig. 17.10). Is the sketch correct? If not, correct it.
Answer: No, the provided sketch is likely incorrect. Common errors in solar system sketches include:
1. **Relative Sizes:** Planets are often drawn with incorrect relative sizes. Jupiter, Saturn, Uranus, and Neptune (the gas giants) should be much larger than Mercury, Venus, Earth, and Mars (the terrestrial planets).
2. **Relative Distances:** The distances between planets are highly disproportionate in most sketches. The inner planets are relatively close to each other, while the outer planets are spaced much farther apart. For example, the distance between Jupiter and Saturn is far greater than the distance between Earth and Mars.
3. **Orbital Paths:** Orbits should be elliptical, not perfectly circular, though for a simplified diagram, slightly elliptical paths are acceptable.
4. **Inclusion of Dwarf Planets/Asteroids:** While not always required, a correct sketch might show the asteroid belt between Mars and Jupiter, and the Kuiper Belt beyond Neptune, where dwarf planets like Pluto reside.
A correct figure would accurately represent these relative sizes and distances, showing the vast empty space in the outer solar system and the correct order of planets from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
In simple words: The sketch is probably wrong because planet sizes and distances are usually drawn incorrectly. A good sketch would show big gas giants, small rocky planets, and the huge gaps between the outer planets in their correct order.

Exam Tip: When assessing or drawing solar system models, pay close attention to the scale of planets and the vast, increasing distances between them as you move away from the Sun.