Solar System — Set 4

Correct Answer: A. Away from the Sun

• **Away from the Sun** = a comet's tail always points away from the Sun because solar wind pushes gas and dust outward. • **Two tails** — comets typically have two tails: an ion tail (pointing directly away from the Sun) and a dust tail (slightly curved). • 💡 Wrong-option analysis: Towards the Sun: impossible as solar wind blows material away from the Sun; Towards the Earth: Earth's position relative to the comet changes, the tail direction does not follow Earth; Away from the Earth: Earth's position is irrelevant to comet tail direction.

Correct Answer: D. Copernicus

• **Copernicus** = Nicolaus Copernicus proposed the Heliocentric model in 1543, placing the Sun at the center of the solar system. • **1543 'De Revolutionibus'** — Copernicus published his heliocentric theory in 'De Revolutionibus Orbium Coelestium' in 1543. • 💡 Wrong-option analysis: Ptolemy: proposed the Geocentric model where Earth is at the center; Newton: formulated laws of gravity and motion, not heliocentrism; Aristotle: supported the Geocentric model.

Correct Answer: D. Venus

• **Venus** = called Earth's 'Twin Sister' because it has nearly identical size, mass, and density to Earth. • **95% of Earth's diameter** — Venus's diameter is about 12,104 km vs Earth's 12,756 km; however, surface temperatures reach 465°C. • 💡 Wrong-option analysis: Mercury: much smaller, no moon, extreme temperature differences; Mars: about half Earth's size; Uranus: a gas giant, far larger than Earth.

Correct Answer: D. Umbra

• **Umbra** = the darkest, innermost part of a shadow during an eclipse where all sunlight is completely blocked. • **Total eclipse zone** — observers within the umbra experience a total eclipse; the Moon's umbra is about 160 km wide on Earth's surface. • 💡 Wrong-option analysis: Antumbra: the region beyond the umbra where the Sun appears as a ring (annular eclipse); Penumbra: the lighter outer shadow where only partial eclipse is seen; Corona: the Sun's outer atmosphere visible during totality.

Correct Answer: A. Mars

• **Mars** = Olympus Mons, the largest and tallest volcano in the solar system, is located on Mars. • **21.9 km height** — Olympus Mons stands 21.9 km high, nearly 3 times the height of Mount Everest (8.85 km). • 💡 Wrong-option analysis: Io: most volcanically active moon of Jupiter but has no Olympus Mons; Earth: Mount Everest is tallest but only 8.85 km; Venus: has many volcanoes but none as tall as Olympus Mons.

Correct Answer: A. Neptune

• **Neptune** = Triton is the largest moon of Neptune and is unique because it has a retrograde orbit (orbits opposite to Neptune's rotation). • **-235°C surface** — Triton is one of the coldest objects in the solar system and is believed to be a captured Kuiper Belt object. • 💡 Wrong-option analysis: Jupiter: its largest moon is Ganymede; Saturn: its largest moon is Titan; Uranus: its largest moon is Titania.

Correct Answer: A. Saturn

• **Saturn** = the only planet with a density less than water (0.69 g/cm³ vs water's 1 g/cm³), so it would theoretically float. • **0.69 g/cm³ density** — Saturn's low density is due to its composition of mostly hydrogen and helium gases. • 💡 Wrong-option analysis: Mars: density is 3.93 g/cm³, far denser than water; Jupiter: density is 1.33 g/cm³, slightly denser than water; Uranus: density is 1.27 g/cm³, also denser than water.

Correct Answer: C. General Relativity

• **General Relativity** = Einstein's Theory of General Relativity (1915) predicted black holes as regions where gravity is so strong nothing, not even light, can escape. • **Event Horizon** — the boundary of a black hole is the event horizon; beyond it, escape velocity exceeds the speed of light. • 💡 Wrong-option analysis: Thermodynamics: deals with heat and energy, not predicting black holes; Quantum Mechanics: deals with subatomic particles, not large-scale gravity; Electromagnetism: deals with electric and magnetic forces.

Correct Answer: A. Gravitational pull of the Moon and Sun

• **Gravitational pull of Moon and Sun** = tides are primarily caused by the Moon's and Sun's gravitational forces acting on Earth's oceans. • **Moon's effect is 2x** — the Moon has about twice the tidal effect of the Sun despite the Sun being more massive, due to the Moon's closer proximity. • 💡 Wrong-option analysis: Earth's rotation only: rotation affects timing of tides but not the primary cause; Solar wind: a stream of charged particles, does not cause ocean tides; Atmospheric pressure: affects weather, not tides.

Correct Answer: C. Long-period Comets

• **Oort Cloud** = a theoretical spherical shell surrounding the solar system believed to be the source of long-period comets (orbital periods over 200 years). • **50,000–100,000 AU distance** — the Oort Cloud extends from about 50,000 to 100,000 AU from the Sun, far beyond the Kuiper Belt. • 💡 Wrong-option analysis: Solar Flares: originate from the Sun's surface activity; Asteroids: mostly found in the asteroid belt between Mars and Jupiter; Meteors: small rocky fragments that burn in Earth's atmosphere.