Solar System — Set 3

Correct Answer: D. Distance

• **Light Year** = a unit of distance representing how far light travels in one year through a vacuum. • **9.46 trillion km** — one light year equals approximately 9.46 × 10¹² km or 63,241 astronomical units. • 💡 Wrong-option analysis: Speed: light-year measures distance, not speed; Intensity: a measure of brightness or power; Time: despite the word 'year', it measures distance not time.

Correct Answer: C. Dust and Ice

• **Dust and Ice** = comets are primarily composed of dust, rock, and frozen gases, often described as 'dirty snowballs'. • **Sublimation tail** — when comets approach the Sun, ice sublimates to form a bright coma and tail that always points away from the Sun. • 💡 Wrong-option analysis: Iron and Nickel: typical composition of metallic asteroids, not comets; Molten rock: describes volcanic lava, not comets; Hydrogen gas: found in gas giants, not the primary comet material.

Correct Answer: B. Jupiter

• **Jupiter** = the Great Red Spot is a persistent high-pressure anticyclonic storm on Jupiter, larger than Earth. • **350+ years** — the Great Red Spot has been continuously observed for over 350 years, making it the longest-known storm in the solar system. • 💡 Wrong-option analysis: Mars: has dust storms but no Great Red Spot; Saturn: has hexagonal polar storm but no Red Spot; Neptune: has a Great Dark Spot which is different.

Correct Answer: D. Mercury

• **Mercury** = has no natural satellites or moons; it is one of only two planets without any moons. • **Venus also moonless** — Venus is the only other planet with no moons; all other planets have at least one natural satellite. • 💡 Wrong-option analysis: Neptune: has 14 known moons, including Triton; Uranus: has 27 known moons; Mars: has 2 moons - Phobos and Deimos.

Correct Answer: D. Spiral

• **Spiral (Barred Spiral)** = the Milky Way is classified as a barred spiral galaxy, with our solar system located in the Orion Arm. • **100,000 light-years** — the Milky Way is approximately 100,000 light-years in diameter and contains 200–400 billion stars. • 💡 Wrong-option analysis: Lenticular: lens-shaped galaxies without spiral arms; Irregular: galaxies with no defined shape; Elliptical: oval-shaped galaxies like Andromeda's companions.

Correct Answer: A. Mars

• **Mars** = Phobos and Deimos are the two small, irregularly shaped moons of Mars, likely captured asteroids. • **Phobos = 9,376 km orbit** — Phobos orbits Mars at only 9,376 km, closer than any other known moon to its parent planet. • 💡 Wrong-option analysis: Jupiter: its major moons are Io, Europa, Ganymede, Callisto; Saturn: its major moon is Titan; Uranus: its major moons are Miranda, Ariel, Umbriel.

Correct Answer: D. Astronomical Unit

• **Astronomical Unit (AU)** = the average distance between Earth and the Sun, used as a standard unit for measuring distances within the solar system. • **150 million km** — one AU equals approximately 149.6 million km, the basis for measuring planetary distances. • 💡 Wrong-option analysis: Light Year: distance light travels in one year (~9.46 trillion km), too large for solar system distances; Parsec: 3.26 light-years, used for interstellar distances; Kilometer: too small a unit for planetary distances.

Correct Answer: B. Neptune

• **Neptune** = generally considered the coldest planet due to its extreme distance from the Sun as an ice giant. • **-214°C average** — Neptune's average temperature is around -214°C; Uranus sometimes records lower temperatures due to its unusual tilt. • 💡 Wrong-option analysis: Jupiter: a gas giant closer to the Sun, not the coldest; Uranus: occasionally records lower temperatures but Neptune is generally colder; Saturn: warmer than both ice giants.

Correct Answer: B. Universe

• **Universe** = the Big Bang Theory explains the origin and expansion of the entire Universe from a high-density, high-temperature state. • **13.8 billion years ago** — the Big Bang occurred approximately 13.8 billion years ago, according to cosmological evidence. • 💡 Wrong-option analysis: Solar System only: the solar system formed much later (4.6 billion years ago) through a different process; Stars: stars formed after the Big Bang but it does not specifically explain star formation; Milky Way Galaxy: formed billions of years after the Big Bang.

Correct Answer: A. Solar Eclipse

• **Solar Eclipse** = occurs when the Moon passes between the Sun and Earth, blocking sunlight partially or fully from reaching Earth. • **New Moon phase** — a solar eclipse can only occur during the New Moon phase when Moon, Sun, and Earth align. • 💡 Wrong-option analysis: Solstice: the position of Earth when the Sun is farthest north or south; Lunar Eclipse: occurs when Earth comes between the Sun and Moon; Equinox: when day and night are equal in length.