Solar System — Set 5

Correct Answer: A. June 21

• **June 21** = the Summer Solstice in the Northern Hemisphere, the longest day of the year when the Sun is directly over the Tropic of Cancer. • **23.5° tilt** — Earth's axial tilt of 23.5° causes the solstices; on June 21, the North Pole is tilted most toward the Sun. • 💡 Wrong-option analysis: March 21: Spring Equinox in Northern Hemisphere; September 23: Autumn Equinox in Northern Hemisphere; December 22: Winter Solstice in Northern Hemisphere (shortest day).

Correct Answer: D. Polaris

• **Polaris** = known as the 'Pole Star' or 'North Star' because it lies nearly directly above Earth's North Pole and appears stationary in the sky. • **430 light-years away** — Polaris is located approximately 430 light-years from Earth in the constellation Ursa Minor. • 💡 Wrong-option analysis: Sirius: the brightest star in the night sky (Canis Major) but not the Pole Star; Vega: part of the Summer Triangle, will become pole star in ~14,000 years; Antares: a red supergiant in Scorpius constellation.

Correct Answer: B. Sunspots

• **Sunspots** = temporary dark patches on the Sun's photosphere caused by concentrations of magnetic field flux, cooler than surrounding areas. • **11-year cycle** — sunspot activity follows an approximately 11-year solar cycle, peaking at solar maximum. • 💡 Wrong-option analysis: Solar Flares: sudden eruptions of energy from the Sun's surface; Solar Winds: streams of charged particles emitted by the Sun; Coronal Holes: dark areas in the corona where solar wind escapes more easily.

Correct Answer: D. Johannes Kepler

• **Johannes Kepler** = formulated the three Laws of Planetary Motion describing how planets orbit the Sun in elliptical paths. • **1609–1619** — Kepler published his first two laws in 1609 and the third law in 1619, replacing the circular orbit model. • 💡 Wrong-option analysis: Copernicus: proposed the heliocentric model; Galileo Galilei: made telescopic discoveries supporting heliocentrism; Isaac Newton: formulated the law of universal gravitation, building on Kepler's work.

Correct Answer: B. Saturn

• **Saturn** = the second-largest planet in the solar system after Jupiter, known for its spectacular ring system. • **116,460 km diameter** — Saturn's equatorial diameter is 116,460 km; despite being the second largest, it is the least dense planet. • 💡 Wrong-option analysis: Uranus: third largest planet by radius; Neptune: fourth largest; Jupiter: the largest planet.

Correct Answer: A. Circle of Illumination

• **Circle of Illumination** = the imaginary line separating the lighted half of Earth from the dark half at any given moment. • **Moves with rotation** — the Circle of Illumination shifts continuously as Earth rotates, and its angle changes with Earth's axial tilt throughout the year. • 💡 Wrong-option analysis: Equator: a fixed line at 0° latitude dividing Northern and Southern hemispheres; Prime Meridian: a fixed line at 0° longitude; International Date Line: at ~180° longitude, marks the calendar day change.

Correct Answer: A. Parsec

• **Parsec** = a unit for measuring large astronomical distances, equal to about 3.26 light-years, derived from parallax of one arcsecond. • **3.26 light-years** — one parsec equals 3.086 × 10¹³ km; kiloparsecs and megaparsecs are used for galaxy and universe-scale distances. • 💡 Wrong-option analysis: Kilometer: too small for interstellar distances; Nautical Mile: used for sea/air navigation (1.852 km); Angstrom: unit for measuring atomic/molecular distances (10⁻¹⁰ m).

Correct Answer: D. 4.6 billion years

• **4.6 billion years** = the approximate age of the Solar System, formed from the gravitational collapse of an interstellar molecular cloud. • **Radiometric dating** — the age is determined by radiometric dating of the oldest meteorites and lunar rocks, confirming 4.568 billion years. • 💡 Wrong-option analysis: 10 billion years: the approximate age of the Sun-like star Kepler-10; 2.5 billion years: when complex cells first appeared on Earth; 13.8 billion years: age of the Universe (Big Bang), not the solar system.

Correct Answer: D. Orion

• **Orion** = a prominent constellation known as 'The Hunter', containing bright stars Betelgeuse and Rigel and the distinctive three-star belt. • **Betelgeuse & Rigel** — Orion contains Betelgeuse (a red supergiant) and Rigel (a blue supergiant), two of the ten brightest stars in the night sky. • 💡 Wrong-option analysis: Cassiopeia: shaped like a 'W' or 'M', named after a queen; Ursa Major: shaped like a bear/big dipper; Leo: shaped like a lion, not a hunter.

Correct Answer: D. Neptune

• **Kuiper Belt** = a circumstellar disc beyond Neptune's orbit containing small icy bodies, dwarf planets (Pluto, Eris, Makemake). • **30–50 AU from Sun** — the Kuiper Belt extends from 30 AU (Neptune's orbit) to about 50 AU from the Sun. • 💡 Wrong-option analysis: Uranus: the Kuiper Belt is far beyond Uranus; Jupiter: the asteroid belt exists between Mars and Jupiter; Saturn: too close to Sun for the Kuiper Belt.