Universe and Space Exercise Solutions | KalviGavani

Universe and Space — Exercise Solutions Guide

Samacheer Kalvi Tamil Nadu State Board Class 7 Science Term 3 Chapter 2 exercise solutions. Solve each exercise first, then check the answers below.

I. Multiple Choice Questions (MCQs)

Q1. Moon's revolution period around Earth in days: (a) 24 (b) 30 (c) 27 (d) 29 Answer: (c) 27 ✓ The Moon takes approximately 27 days to complete one revolution around Earth.

Q2. If the Moon is near the star Karthikai today, its position after 27 days: (a) Karthikai (b) Bharani (c) Pooram (d) Asvini Answer: (d) Asvini ✓ After one full revolution, the Moon shifts eastward relative to the stars.

Q3. Telescope inventor: (a) Han Lippershey (b) Galileo (c) Newton (d) Kepler Answer: (a) Han Lippershey ✓ Hans Lippershey invented the telescope; Galileo first used it for astronomical observations.

Q4. Galaxy type with young, hot stars: (a) Elliptical galaxy (b) Irregular galaxy (c) Barred spiral galaxy (d) Spiral galaxy Answer: (d) Spiral galaxy ✓ Spiral galaxies contain young, hot stars in their spiral arms along with gas and dust.

Q5. ISRO satellite launch for 4-ton capability: (a) GSAT-14 (b) GSAT-9 (c) GSAT-17 (d) GSAT-19 Answer: (d) GSAT-19 ✓ GSAT-19 was launched by GSLV Mark III-D1, demonstrating ISRO's 4-ton launch capability.

Additional MCQs

AQ1. Milky Way galaxy type: (a) Elliptical (b) Irregular (c) Spiral (d) Barred spiral Answer: (c) Spiral ✓ The Milky Way is a spiral galaxy containing our solar system.

AQ2. Stars mainly consist of: (a) Oxygen and carbon (b) Hydrogen and helium (c) Nitrogen and oxygen (d) Iron and helium Answer: (b) Hydrogen and helium ✓ Stars are primarily composed of hydrogen and helium gases undergoing nuclear fusion.

AQ3. Great Bear / Saptha Rishi Mandalam: (a) Ursa Major (b) Ursa Minor (c) Orion (d) Cassiopeia Answer: (a) Ursa Major ✓ Ursa Major is known as the Great Bear or Saptha Rishi Mandalam in Indian astronomy.

AQ4. GSLV stands for: (a) Geostationary Satellite Launch Vehicle (b) Geosynchronous Satellite Launch Vehicle (c) Galactic Space Launch Vehicle (d) Geocentric Satellite Launch Vehicle Answer: (b) Geosynchronous Satellite Launch Vehicle ✓ GSLV stands for Geosynchronous Satellite Launch Vehicle, used for placing satellites in geosynchronous orbits.

AQ5. Parsec equals how many light years: (a) 1.5 (b) 2.26 (c) 3.0 (d) 3.26 Answer: (d) 3.26 ✓ One parsec equals approximately 3.26 light years, a unit used for measuring stellar distances.

AQ6. Hottest planet: (a) Mercury (b) Venus (c) Mars (d) Jupiter Answer: (b) Venus ✓ Venus is the hottest planet due to its thick atmosphere causing a strong greenhouse effect, despite not being closest to the Sun.

AQ7. First artificial satellite: (a) Sputnik-1 (b) Explorer-1 (c) Aryabhatta (d) Apollo-11 Answer: (a) Sputnik-1 ✓ Sputnik-1 was launched by Russia (USSR) on 4 October 1957, marking the beginning of the Space Age.

AQ8. Nearest galaxy to Milky Way: (a) Andromeda (b) Triangulum (c) Large Magellanic Cloud (d) Sombrero Answer: (a) Andromeda ✓ The Andromeda galaxy is the nearest major galaxy to the Milky Way.

AQ9. Earth orbits Sun in how many days: (a) 360 (b) 365 (c) 366 (d) 350 Answer: (b) 365 ✓ Earth completes one revolution around the Sun in approximately 365 days.

AQ10. Big Bang approximately how many billion years ago: (a) 10 (b) 12 (c) 14 (d) 16 Answer: (c) 14 ✓ The Big Bang is estimated to have occurred approximately 14 billion years ago.

II. Fill in the Blanks

1. Waxing of Moon means growing or expanding. 2. Heliocentric model proposed by Nicolus Copernicus. 3. Prevailing model of Universe evolution — The Big Bang Theory. 4. Large constellation covering much of the sky — Ursa Major. 5. India's first satellite — Aryabhatta.

Additional Fill in the Blanks

6. Totality of everything known to exist — Universe. 7. One half of this body is always Sun-illuminated — Moon. 8. Reversal of planetary direction — Retrograde motion. 9. Telescope inventor — Hans Lippershey (Galileo first used it to study the sky). 10. Naked-eye bright planet — Venus. 11. Event of matter expanding from a single point — Big Bang. 12. Distance light travels in one year — Light year. 13. Average Earth-Sun distance — Astronomical unit. 14. Milky Way diameter (in light years) — 100,000. 15. Solar system's average speed — 828,000 km/h. 16. India's first satellite launched by Soviet Union on 19 April 1975 — Aryabhatta.

III. True or False (with corrections)

Q1. On full Moon day, Moon rises in the West. Answer: False. The Moon always rises in the East, just like the Sun.

Q2. Crescent means less than half illuminated. Answer: True. ✓

Q3. Galileo accepted the geocentric model. Answer: False. Galileo supported the heliocentric model, which places the Sun at the center.

Q4. Milky Way is an elliptical galaxy. Answer: False. The Milky Way is a spiral galaxy, not an elliptical galaxy.

Q5. Venus has no Moon. Answer: True. ✓

Additional True/False

Q6. Full Moon day, Moon rises in the west when Sun sets in the west. Answer: False. The Moon rises in the east on a full Moon day, even as the Sun sets in the west.

Q7. Moon orbits Earth in approximately 27 days. Answer: True. ✓

Q8. Gibbous means more than half illuminated. Answer: True. ✓

Q9. Kepler's Venus observations supported heliocentric theory. Answer: False. It was Galileo's observations of Venus that supported the heliocentric theory, not Kepler's.

Q10. All galaxies are moving away from us. Answer: True. ✓ — This observation supports the expanding universe concept.

Q11. Our solar system is in a barred spiral galaxy. Answer: True. ✓ — Recent studies classify the Milky Way as a barred spiral galaxy.

Q12. Constellations are optical appearances, not real physical groupings. Answer: True. ✓ — Stars in a constellation may be at vastly different distances; they only appear grouped from Earth.

Q13. All planets except Mercury have Moons. Answer: False. Both Mercury and Venus have no Moons.

Q14. ISRO's vision involves harnessing space technology for national development. Answer: True. ✓

Q15. NASA sent Chandrayaan-1. Answer: False. ISRO (Indian Space Research Organisation) sent Chandrayaan-1.

IV. Match the Following

Set 1: Satellite and Launch Vehicle

Set 2: Scientists and Theories

Set 3: Constellations

Set 4: Galaxy Types

V. Analogy

1. Older stars : elliptical galaxies :: younger stars : irregular galaxies 2. Nearest galaxy : Andromeda :: nearest star : Alpha Centauri

VI. Very Short Answers

Q1. What is the difference between crescent and gibbous phases? Answer: Crescent means less than half of the Moon's visible surface is illuminated; gibbous means more than half is illuminated.

Q2. Two planets that are never seen in the midnight sky. Answer: Mercury and Venus — they are inner planets and always appear near the Sun.

Q3. Days Mars takes to orbit the Sun. Answer: 687 days.

Q4. Venus phase when it shows a small apparent size. Answer: Gibbous phase — Venus appears smaller in gibbous phase because it is farther from Earth.

Q5. Only evidence for the Big Bang Theory. Answer: Cosmic microwave background radiation.

Q6. Galaxy type with abundant gas and dust. Answer: Spiral galaxy.

Q7. Country that launched the first artificial satellite. Answer: Russia (USSR) — launched Sputnik-1 on 4 October 1957.

Additional Very Short Answers

Q8. Planets with no Moons. Answer: Mercury and Venus.

Q9. Galaxy we live in. Answer: Milky Way.

Q10. Star that appears stationary at night. Answer: Pole star (Polaris / Dhruva).

Q11. Indian name for Ursa Minor. Answer: Laghu Saptarishi.

Q12. Planets with more than 60 Moons. Answer: Jupiter and Saturn.

Q13. Distance of solar system from galaxy center. Answer: 27,000 light years.

Q14. Distance light travels in one year. Answer: Light year — approximately 9.46 trillion km.

Q15. Another name for Big Dipper. Answer: Ursa Major.

Q16. What are constellations? Answer: Stars forming recognizable patterns when viewed from Earth; they are optical groupings, not physical ones.

VII. Short Answers

Q1. What is the epicyclic model? Answer: An early modification to the geocentric model where each planet moves in a small circle (epicycle) whose center moves along a larger circle around the Earth. This model attempted to explain the observed retrograde motion of planets while keeping Earth at the center.

Q2. Name four types of galaxies. Answer: The four types are: (1) Spiral galaxy, (2) Elliptical galaxy, (3) Irregular galaxy, and (4) Barred spiral galaxy.

Q3. What is a constellation? Answer: A recognizable pattern of stars in the night sky as viewed from Earth. The International Astronomical Union (IAU) has classified 88 constellations. Stars in a constellation may be at vastly different distances — they are optical groupings, not physical clusters.

Q4. Expand PSLV and GSLV. Answer: PSLV — Polar Satellite Launch Vehicle; GSLV — Geosynchronous Satellite Launch Vehicle.

Additional Short Answers

Q5. Why does the Moon change shape daily? Answer: The Moon revolves around the Earth, and as its position relative to the Earth and Sun changes, the illuminated portion visible from Earth changes continuously, producing the phases of the Moon.

Q6. What is first quarter? Answer: When the Sun, Earth, and Moon form a 90-degree angle during the waxing phase, half of the Moon's visible surface is illuminated — this is called the first quarter.

Q7. Write a note on planets. Answer: Planets revolve around the Sun. They do not emit their own light but reflect sunlight. They have predictable orbits and vary in size, composition, and number of Moons.

Q8. Write a note on ISRO. Answer: ISRO (Indian Space Research Organisation) is India's national space agency, headquartered in Bengaluru. Its vision is to harness space technology for national development. ISRO has launched satellites like Aryabhatta, Chandrayaan-1 and 2, and Mangalyaan.

Q9. Why is Earth a unique planet? Answer: Earth is the only known planet supporting life, thanks to its atmosphere, availability of water, and suitable temperature range — all essential conditions for living organisms.

Q10. Write a note on artificial satellites. Answer: Artificial satellites are man-made objects orbiting a planet. The first was Sputnik-1 (Russia, 1957). India's first satellite was Aryabhatta (1975). They are used for TV and radio broadcasting, agriculture monitoring, mineral detection, weather forecasting, and navigation.

Q11. Why do stars twinkle? Answer: Stars are very distant and appear as tiny dots. Atmospheric disturbances (variations in temperature and density of air layers) prevent starlight from reaching us in a straight path, causing the twinkling effect.

VIII. Detailed Answers

Q1. Explain the waxing and waning phases of Venus. Answer: As Venus orbits the Sun, it shows phases similar to the Moon. When Venus is close to Earth (between Earth and Sun), it appears brighter and larger, showing a crescent phase. When Venus is on the far side of the Sun, it appears smaller and shows a gibbous phase. The key insight is that the gibbous phase appears smaller than the crescent phase — this can only be explained if Venus orbits the Sun, not the Earth. This observation by Galileo provided strong evidence for the heliocentric model.

Q2. Write short notes on constellations. Answer: The IAU has classified 88 constellations. Two important ones are:

• Ursa Major (Saptha Rishi Mandalam): Contains the Big Dipper, a group of 7 prominent stars. It is visible throughout the year in the northern sky.
• Ursa Minor (Laghu Saptarishi): Contains the Little Dipper, also with 7 stars. The Pole Star (Polaris / Dhruva) is located at the end of the Little Dipper's handle and appears nearly stationary in the night sky.

Other well-known constellations include Orion (the Hunter) and Cassiopeia.

Q3. Explain the origin of the Universe. Answer: Observations show that all galaxies are moving away from each other, indicating the universe is expanding. The prevailing theory — the Big Bang Theory — states that all matter was once confined to a single point, thousands of times smaller than a pinhead. About 14 billion years ago, a sudden expansion occurred, producing the present universe. Space and time themselves emerged from this event. The cosmic microwave background radiation discovered in 1965 is the strongest evidence supporting the Big Bang Theory.

IX. Higher Order Thinking Skills (HOTS)

Q1. Neelan says Earth is the only planet with life. Mala opposes this view. Discuss. Answer: Neelan is correct that Earth is the only known planet with confirmed life, due to its unique conditions: liquid water, oxygen-rich atmosphere, suitable temperature, and protective magnetic field. However, Mala's counter-argument is valid: there are billions of stars in our galaxy alone, and billions of galaxies in the universe. Many of these stars may have orbiting planets (exoplanets) with conditions favorable for life. The sheer number increases the probability that life could exist elsewhere, even if not yet discovered.

AQ1. Do stars emit light only at night? Answer: No. Stars emit light continuously, day and night. We cannot see them during the day because the Sun's brightness overwhelms their faint light in our sky.

AQ2. Can we ever see the far side of the Moon from Earth? Answer: No. The Moon's revolution period around Earth equals its rotation period (tidal locking), so it always faces Earth with the same side. The far side is never visible from Earth.

Common Mistakes to Avoid

1. Calling the Sun a planet — The Sun is a star, not a planet. It produces its own light through nuclear fusion. 2. Saying all planets have Moons — Mercury and Venus have no Moons. 3. Confusing heliocentric and geocentric models — Heliocentric: Sun at center (Copernicus, Galileo); Geocentric: Earth at center (Ptolemy). 4. Saying constellations are physically close groups — Constellations are optical appearances from Earth; their stars may be at vastly different distances. 5. Confusing spiral and elliptical galaxies — Spiral galaxies have young, hot stars and gas; elliptical galaxies have older stars in globular clusters. 6. Forgetting that the Milky Way is a spiral galaxy — The Milky Way is classified as a spiral (specifically, a barred spiral) galaxy, not an elliptical galaxy. 7. Saying the Moon produces its own light — The Moon reflects sunlight; it has no light of its own.

Exam Checklist

• [ ] Can state the Moon's revolution period (27 days)
• [ ] Can name and describe the four types of galaxies (spiral, elliptical, irregular, barred spiral)
• [ ] Can differentiate between heliocentric and geocentric models
• [ ] Can identify 88 constellations and describe Ursa Major and Ursa Minor
• [ ] Can explain India's space programme (ISRO, Aryabhatta, PSLV, GSLV)
• [ ] Can explain the Big Bang Theory and its evidence
• [ ] Can define light year and astronomical unit
• [ ] Can explain why stars twinkle
• [ ] Can name planets with no Moons (Mercury and Venus)
• [ ] Can list uses of artificial satellites
• [ ] Can explain waxing and waning phases of the Moon and Venus
• [ ] Can match Indian satellites with their launch vehicles