FC - IntroductionSolarSystem

35 question–and–answer flashcards covering core concepts from the lecture on Solar System structure, planetary definitions, dynamics, historical astronomy, and formation.

How many officially recognized planets are in the Solar System today?

Eight

According to the 2006 IAU definition, what three criteria must a celestial body satisfy to be called a planet?

(a) Orbit the Sun, (b) have enough mass to reach hydrostatic equilibrium (round shape), and (c) clear its orbital neighborhood

Which single IAU planet-criterion is NOT fulfilled by a dwarf planet?

It has not cleared the neighborhood around its orbit

Why is Pluto classified as a dwarf planet and not a planet?

Because it does not clear its orbital neighborhood and is part of the Kuiper Belt

What is an Astronomical Unit (AU) and what is its exact length?

The average Earth–Sun distance; exactly 149,597,870,700 meters

What is the ecliptic plane?

The plane of Earth’s orbit around the Sun, used as the reference for Solar System coordinates

In what configuration is an outer planet opposite the Sun in Earth’s sky?

Opposition

In what rotational sense do most planets spin relative to their orbital motion around the Sun?

The same (prograde) direction

Name two Solar System bodies that rotate in an unusual or retrograde direction.

Venus and Uranus (Pluto also rotates retrograde)

What is the definition of obliquity?

The angle between a planet’s rotation axis and the normal to its orbital plane

What is Earth’s axial precession period?

About 25,800 years

What is Mars’ axial precession period?

About 175,000 years

Which two planets are in a 3:2 orbital resonance?

Neptune and Pluto

Which planet exhibits a 3:2 spin–orbit resonance with the Sun?

Mercury (three rotations for every two revolutions)

What does the Titius–Bode law attempt to predict?

The spacing (semi-major axes) of planetary orbits

Which planets are classified as terrestrial planets?

Mercury, Venus, Earth, and Mars

Name the largest asteroid and state its approximate diameter.

1 Ceres, roughly 950 km

How many Galilean satellites does Jupiter have, and what are their names?

Four: Io, Europa, Ganymede, and Callisto

Which Saturn moon possesses a dense atmosphere?

Titan

Which Saturn moon is famous for seasonal cryovolcanism?

Enceladus

What letter names designate the main rings of Saturn (from innermost bright ring outward)?

D, C, B, A (with the Cassini Division between rings B and A)

What is unusual about Uranus’ rotation axis?

It lies almost in the planet’s orbital plane (tilt ~98°)

Which spacecraft performed the only fly-by of Uranus?

Voyager 2 in January 1986

Approximately how many moons are currently known to orbit Neptune?

Fourteen

Which Neptunian moon had its south pole imaged by Voyager-2?

Triton

What is the Kuiper Belt?

A disc-like region beyond Neptune (~30–50 AU) containing many icy Trans-Neptunian Objects

What is the Oort Cloud?

A hypothetical spherical shell of icy bodies 2,000–200,000 AU from the Sun, source of long-period comets

What is the closest star system to the Sun and roughly how far away is it?

Alpha Centauri system at about 4.4 light-years

Who first proposed a heliocentric model with Earth orbiting the Sun around 300 BC?

Aristarchus of Samos

Who reintroduced the heliocentric model in the 16th century?

Nicolaus Copernicus

Whose precise observations provided the data for Kepler’s laws?

Tycho Brahe

What do Kepler’s three laws describe in general terms?

The shapes, speeds, and period–distance relationship of planetary orbits

Who formulated the law of universal gravitation?

Sir Isaac Newton

What is the frost line in a protoplanetary disk?

The distance from the young Sun where temperatures are low enough for volatile ices to remain solid

Approximately how old is the Solar System?

About 4.568 billion years