Solar System — Set 7

Correct Answer: B. Total Lunar Eclipse

• **Total Lunar Eclipse** = a Blood Moon occurs when Earth's atmosphere scatters blue light and refracts red light onto the Moon during a total lunar eclipse. • **Rayleigh scattering** — the same principle that makes sunrises/sunsets red causes the Moon to appear copper-red during a total lunar eclipse. • 💡 Wrong-option analysis: Partial Solar Eclipse: Moon partially covers the Sun, not related to Blood Moon; Total Solar Eclipse: Moon fully covers the Sun from Earth's view; Winter Solstice: an astronomical event about Earth's tilt, not an eclipse.

Correct Answer: C. Geoid (Oblate Spheroid)

• **Geoid (Oblate Spheroid)** = Earth's shape is slightly flattened at the poles and bulging at the equator due to centrifugal force from rotation. • **43 km difference** — Earth's equatorial diameter (12,756 km) is about 43 km larger than its polar diameter (12,714 km). • 💡 Wrong-option analysis: Flat Disk: Earth is spherical, not flat; Ellipse: describes a 2D shape, not 3D; Perfect Sphere: not accurate as Earth is slightly oblate due to rotation.

Correct Answer: C. Europa

• **Europa** = Jupiter's moon Europa is believed to have a vast subsurface ocean of liquid water beneath its icy crust, making it a prime candidate for extraterrestrial life. • **100 km deep ocean** — Europa's subsurface ocean is estimated to be around 100 km deep, containing more liquid water than all of Earth's oceans combined. • 💡 Wrong-option analysis: Phobos: a small, rocky moon of Mars with no subsurface ocean; Titan: has liquid methane/ethane lakes on its surface, not a liquid water ocean; Moon (Luna): no known subsurface liquid water ocean.

Correct Answer: C. Difference between high and low tide is minimum

• **Minimum tidal range** = during Neap Tides, the difference between high and low tides is at its minimum because the Sun and Moon are at right angles. • **Quarter Moon phases** — Neap Tides occur during the first and third quarter Moon phases when the Sun, Earth, and Moon form a 90° angle. • 💡 Wrong-option analysis: Difference between high and low tide is maximum: this describes Spring Tides (full/new moon); Highest high tides: characteristic of Spring Tides; Lowest low tides: also a characteristic of Spring Tides, not Neap Tides.

Correct Answer: D. Spiral

• **Spiral** = Andromeda is a spiral galaxy (Messier 31), the largest galaxy in our Local Group and the nearest major galaxy to the Milky Way. • **2.537 million light-years** — Andromeda is approximately 2.537 million light-years away and is on a collision course with the Milky Way in ~4.5 billion years. • 💡 Wrong-option analysis: Dwarf: Andromeda is actually the largest galaxy in the Local Group; Irregular: no defined structure; Elliptical: oval-shaped like M87, different from Andromeda's spiral arms.

Correct Answer: A. Alignment of Sun, Earth, and Moon

• **Syzygy** = the straight-line alignment of three or more celestial bodies, most commonly the Sun, Earth, and Moon causing eclipses and spring tides. • **Causes eclipses** — solar and lunar eclipses both occur during syzygy: solar when Moon is between Sun and Earth, lunar when Earth is between Sun and Moon. • 💡 Wrong-option analysis: The closest point to the sun: that is perihelion; The explosion of a star: that is a supernova; The formation of a black hole: caused by stellar collapse, unrelated to syzygy.

Correct Answer: C. Jupiter

• **Jupiter** = rotates on its axis the fastest of all planets, completing one rotation in just under 10 hours. • **9 hours 56 minutes** — Jupiter's rapid rotation causes it to bulge at the equator; its equatorial diameter is 9,275 km larger than its polar diameter. • 💡 Wrong-option analysis: Mars: rotation period is about 24.6 hours, similar to Earth; Earth: rotates in approximately 24 hours; Venus: the slowest rotating planet at 243 Earth days per rotation.

Correct Answer: C. Carbon Dioxide

• **Carbon Dioxide** = makes up about 95% of Mars's thin atmosphere, which is approximately 100 times thinner than Earth's. • **0.6% of Earth's pressure** — Mars's atmospheric pressure is only about 0.6% of Earth's, making it insufficient to retain heat or liquid water. • 💡 Wrong-option analysis: Oxygen: only about 0.13% of Mars's atmosphere; Hydrogen: trace amounts only; Nitrogen: about 2.6% of Mars's atmosphere, not the primary component.

Correct Answer: D. Black Hole

• **Black Hole** = the Event Horizon is the boundary surrounding a black hole beyond which nothing, not even light, can escape its gravitational pull. • **'Point of no return'** — once matter crosses the event horizon, it is inevitably drawn into the singularity at the black hole's center. • 💡 Wrong-option analysis: Solar Flare: a burst of radiation from the Sun's surface, not related to event horizons; Supernova: a stellar explosion that can create black holes; Nebula: a cloud of gas and dust, not a black hole phenomenon.

Correct Answer: C. International Astronomical Union (IAU)

• **International Astronomical Union (IAU)** = the official body responsible for naming and classifying celestial objects, founded in 1919. • **Founded 1919** — the IAU also famously reclassified Pluto as a dwarf planet in 2006 and sets standards for all astronomical nomenclature. • 💡 Wrong-option analysis: ISRO: Indian Space Research Organisation, a national space agency; NASA: US space agency, does not have authority to name celestial bodies officially; United Nations: an intergovernmental organization, not involved in astronomical naming.