Samacheer Kalvi 9th Science Universe Exercise Solutions

The Universe is the totality of all matter, energy, space, and time. It contains billions of galaxies, each with billions of stars.

A galaxy is a vast system of stars, dust, gas, and dark matter bound together by gravity. Our galaxy is called the Milky Way (known as Akasha Ganga in Tamil/Indian tradition).

A light year is the distance that light travels in one year at the speed of approximately 3 × 10⁵ km/s. 1 light year = speed of light × seconds in one year = 3 × 10⁵ × 365.25 × 24 × 3600 ≈ 9.46 × 10¹² km.

Venus has a thick atmosphere of carbon dioxide that creates a strong greenhouse effect, trapping heat and making its surface temperature (~465°C) higher than Mercury's (~430°C during the day but extremely cold at night).

Asteroids are small, rocky bodies orbiting the Sun. Most are found in the asteroid belt, a region between the orbits of Mars and Jupiter.

Aryabhata, launched on 19 April 1975, was India's first satellite. It was named after the ancient Indian mathematician and astronomer.

A comet is a small icy body that orbits the Sun in a highly elliptical path.

• Nucleus (head): Made of ice, dust, and rocky material (often called a "dirty snowball").
• Coma: A glowing envelope of gas and dust that surrounds the nucleus when the comet approaches the Sun.
• Tail: Formed when solar radiation vaporises the ice; the tail always points away from the Sun due to solar wind.
• Comets have very long orbital periods. Halley's Comet appears approximately every 76 years (next visible in 2061).

Solar Eclipse:

• Occurs when the Moon comes between the Sun and Earth.
• The Moon casts a shadow on Earth, blocking sunlight.
• Occurs only during a New Moon day.
• Types: Total, Partial, and Annular solar eclipse.

Lunar Eclipse:

• Occurs when the Earth comes between the Sun and Moon.
• The Earth casts a shadow on the Moon.
• Occurs only during a Full Moon day.
• The Moon appears reddish during a total lunar eclipse ("Blood Moon").

Artificial satellites are human-made objects placed in orbit around the Earth for various purposes.

Examples: 1. Communication satellites (e.g., INSAT series): Used for television broadcasting, telephone, and internet communication. 2. Weather satellites (e.g., INSAT, Kalpana-1): Used for weather forecasting, cyclone tracking, and climate monitoring.

Other uses: Navigation (GPS), scientific research, military surveillance, remote sensing (resource mapping, agriculture monitoring).

• Aryabhata (1975): India's first satellite.
• Chandrayaan-1 (2008): India's first lunar probe; confirmed the presence of water molecules on the Moon.
• Mangalyaan / MOM (2013): India's first interplanetary mission to Mars; India became the first Asian nation and fourth space agency to reach Mars. It was achieved in the very first attempt, at a remarkably low cost.
• Chandrayaan-2 (2019): Second lunar mission with an orbiter, lander (Vikram), and rover (Pragyan).
• Chandrayaan-3 (2023): Successfully soft-landed near the Moon's south pole — India became the fourth country to soft-land on the Moon and the first to land near the lunar south pole.
• Gaganyaan (planned): India's first crewed space mission.

Seasons occur due to two reasons: 1. Tilt of Earth's axis: Earth's axis is tilted at 23.5° to the plane of its orbit. 2. Revolution around the Sun: As Earth orbits the Sun, different parts of Earth receive varying amounts of sunlight at different times of the year.

When the Northern Hemisphere tilts towards the Sun, it experiences summer while the Southern Hemisphere experiences winter, and vice versa. At the equator, sunlight is nearly direct year-round, so seasonal variation is minimal.

Constellations are groups of stars that form recognisable patterns or shapes in the night sky. They were named by ancient astronomers after mythological figures, animals, or objects.

Four well-known constellations: 1. Ursa Major (Great Bear / Saptarishi) — contains the Big Dipper 2. Orion (The Hunter) — visible in winter with the prominent three-star belt 3. Cassiopeia — W-shaped constellation in the northern sky 4. Scorpius (The Scorpion) — summer constellation with the bright star Antares

The solar system consists of the Sun at the centre and all celestial bodies bound to it by gravity — eight planets, their moons, dwarf planets, asteroids, comets, and meteoroids.

The Sun:

• A medium-sized star; nearest star to Earth (150 million km / 1 AU).
• Composed mainly of hydrogen (70%) and helium (28%).
• Produces energy through nuclear fusion (hydrogen → helium).
• Surface temperature: ~5,500°C; core temperature: ~15 million°C.

Inner (Terrestrial) Planets:

1. Mercury: Smallest planet; closest to the Sun; no atmosphere; extreme temperature variation (~430°C day to –180°C night); no moons; no rings.

2. Venus: Similar in size to Earth ("Earth's twin"); hottest planet (~465°C) due to greenhouse effect; thick CO₂ atmosphere; rotates in retrograde (east to west); no moons.

3. Earth: Only known planet with life; 71% water surface; one natural satellite (Moon); moderate temperature; suitable atmosphere with nitrogen and oxygen.

4. Mars: Called the "Red Planet" due to iron oxide on surface; thin CO₂ atmosphere; two small moons (Phobos and Deimos); has polar ice caps; potential for future human colonisation.

Outer (Jovian) Planets:

5. Jupiter: Largest planet; Great Red Spot (a giant storm); at least 90 moons (Ganymede is the largest moon in the solar system); strong magnetic field; gas giant (hydrogen, helium).

6. Saturn: Famous ring system made of ice and rock particles; second largest planet; least dense planet (would float on water); 140+ moons (Titan is the largest, with a thick atmosphere).

7. Uranus: Rotates on its side (axial tilt ~98°); appears blue-green due to methane; has rings; 27 known moons; discovered by William Herschel (1781).

8. Neptune: Farthest planet; appears blue due to methane; strongest winds in the solar system (~2,000 km/h); 14 known moons (Triton orbits in retrograde).

Differences between Stars and Planets:

Brief Life Cycle of a Star:

1. Nebula: A star begins as a cloud of gas and dust (nebula). Gravity causes the cloud to contract and heat up.

2. Protostar: As the nebula contracts, it forms a protostar — a hot, dense ball of gas not yet hot enough for fusion.

3. Main Sequence Star: When the core temperature reaches ~10 million°C, nuclear fusion begins (hydrogen → helium). The star enters a long stable phase. Our Sun is currently in this stage.

4. Red Giant / Supergiant: When hydrogen fuel depletes, the core contracts and the outer layers expand and cool, forming a red giant (for medium stars like the Sun) or supergiant (for massive stars).

5. End Stage:

• Medium stars (like the Sun): Shed outer layers → form a planetary nebula → core becomes a white dwarf → eventually cools to a black dwarf.
• Massive stars: Explode as a supernova → core collapses to form a neutron star or black hole (depending on mass).

India's space programme is managed by ISRO (Indian Space Research Organisation), established in 1969, headquartered in Bengaluru. Key launch centres: Satish Dhawan Space Centre (Sriharikota).

Key Missions and Achievements:

1. Aryabhata (1975): India's first satellite, launched by a Soviet rocket. Marked India's entry into space.

2. SLV-3 (1980): India's first successful indigenous satellite launch vehicle, placing Rohini satellite in orbit.

3. INSAT Series (1983 onwards): A series of multipurpose geostationary satellites for telecommunications, broadcasting, and meteorology. Revolutionalised TV and weather forecasting in India.

4. Chandrayaan-1 (2008): India's first lunar mission. Made the historic discovery of water molecules on the Moon's surface. Carried 11 scientific instruments.

5. Mangalyaan / Mars Orbiter Mission (2013): India's first interplanetary mission. India became the first Asian nation and the fourth space agency to reach Mars. Achieved on the very first attempt at a fraction of the cost of similar missions globally (approx. ₹450 crore / $74 million).

6. Chandrayaan-2 (2019): Comprised an orbiter, lander (Vikram), and rover (Pragyan). While the orbiter continues to function successfully, the lander lost communication during descent.

7. Chandrayaan-3 (2023): Successfully soft-landed near the Moon's south pole on 23 August 2023. India became the fourth country to soft-land on the Moon and the first to land near the lunar south pole. The Pragyan rover conducted in-situ experiments.

8. Gaganyaan (planned): India's first crewed space mission. Will carry Indian astronauts (Gaganauts) to low Earth orbit. A major step toward human spaceflight capability.

9. Aditya-L1 (2023): India's first space-based solar observatory, placed at the Lagrange Point L1 to study the Sun.

Significance:

• ISRO is known for cost-effective, reliable missions.
• India's space programme supports telecommunications, weather forecasting, disaster management, navigation (NavIC), and resource monitoring.
• Has placed India among the world's leading space-faring nations.