Chapter 2. Solar System
Recommended Article: 【Earth Science】 Table of Contents for Earth Science
1. Solar System
2. Sun
3. Earth
4. Moon
5. Planets
6. Asteroids
7. Comets
8. Meteoroids
a. Proof of the Coplanarity of Binary Systems
1. Solar System
⑴ Theories about the Origin of the Solar System: The Nebular Hypothesis is considered the most plausible.
① Kant, Laplace’s Nebular Hypothesis
② T.C. Chamberlin, F.R. Moulton’s Planetesimal Hypothesis
③ Jeans’ Tidal Hypothesis
④ Lyttleton’s Close Encounter Hypothesis
⑤ Weizsäcker’s Nebular Hypothesis
⑵ 1st Supernova Explosion: A supernova explosion occurred near the Milky Way’s spiral arm.
⑶ 2nd Formation of the Solar Nebula: The materials in the stable state of our galaxy became uneven, forming the solar nebula.
⑷ 3rd Contraction of the Nebula: The solar nebula contracts due to gravity and gradually starts rotating.
⑸ 4th Formation of Primitive Sun: As the nebula contracts, the center becomes hotter and denser, forming the primitive sun.
⑹ 5th Formation of Primitive Disk: The outer rotation of the primitive sun accelerates, forming a flat disk-shaped primitive disk.
⑺ 6th Core of Primitive Sun becomes hotter due to gravitational contraction.
⑻ 7th Primitive Disk forms multiple rings while rotating.
⑼ 8th Formation of Planetesimals: Gases and dust conglomerate in each ring, forming numerous planetesimals.
⑽ 9th Primitive Sun becomes the Sun through hydrogen fusion reactions in its core.
⑾ 10th Formation of Primitive Planets: Planetesimals collide and form primitive planets. They later grow into complete planets.
⑿ 11th Formation of the Solar System: Remaining gases and dust are expelled from the solar system by solar wind.
2. Sun
⑴ Characteristics
① Diameter: About 1,390,000 km = Earth’s diameter × 109
② Mass: 2 × 10^30 kg = Earth’s mass × 330,000
③ Rotation Period: 25 days
④ Composition: Mostly hydrogen and helium, with elements like sodium, magnesium, iron, etc.
⑤ Surface Temperature: 6,000 K
⑥ Core Temperature: 16,000,000 × 10^7 K
⑦ Core Pressure: 3,000,000,000 (3 billion) atm
⑧ Surface Gravity = Earth’s surface gravity × 28
⑵ Structure
① Core: Energy generation through hydrogen fusion
② Radiative Zone: Thickness of about 370,000 km. Transfers energy from core to convection zone.
③ Convection Zone: Lies between the radiative zone and the convective zone. Source of the magnetic field.
④ Convective Zone: Transfers heat through convection, limits material entry and exit.
⑶ Sun’s Surface
① Photosphere: The visible surface of the Sun. Sunspots are observed.
○ Matter exists in plasma state, and blackbody radiation is emitted.
○ Prominences: Flame-like eruptions from the photosphere.
○ Solar Flares: Explosions of gas similar to gas explosions.
○ Granulation: Cellular pattern underneath the photosphere.
○ Bright areas: Hot material rises.
○ Dark areas: Cooler material sinks.
② Chromosphere: Sun’s atmosphere. Eruptions and prominences exist.
○ Plages: Lower part of the chromosphere.
○ Corona: Outermost layer of the solar atmosphere.
○ Upper chromospheric temperature is higher than the upper photospheric temperature.
③ Sunspots
○ Cause: Interference due to strong magnetic fields affecting convection.
○ Shape: Sunspots are cooler areas than the surrounding surface.
Figure 1. Shape of a Sunspot
○ Sunspot Cycle: Period of 11.1 years with spots appearing and disappearing.
Figure 2. Variation in Sunspot Numbers
○ Sunspot Movement
Figure 3. Movement of Sunspots
○ Observing Sunspots: When the Sun is at its zenith, and the observer faces the Sun, the left side is east, and the right side is west.
○ Sun rotates counterclockwise when viewed from above the Sun’s north pole. It’s also called west to east rotation.
○ Sunspots observed at noon shift from east to west as time passes.
○ Sun’s rotation speed is fastest at the equator: its rotation period is shortest at the equator.
○ Earth’s Orbital Period E, Sunspot Rotation Period S, Observed Period P on Earth
⑷ Solar Radiation
① Solar Constant: 1.94 cal / min·㎠
② Fraunhofer Lines: Absorption lines in solar spectrum
○ Reason: Light from the Sun’s surface is selectively absorbed by substances in the solar atmosphere.
③ Nuclear Fusion Theory: High-temperature hydrogen nuclei transform into helium nuclei, releasing energy.
3. Earth
⑴ 1st Formation of Primitive Earth: Primitive Earth formed during the process of forming primitive planets from the solar nebula.
⑵ 2nd Light gases like hydrogen escape into space. Heavy gases like nitrogen remain, forming the atmosphere.
⑶ 3rd Accretion of Planetesimals: Planetesimals collide and merge with primitive Earth, increasing its size and mass.
⑷ 4th Increased Temperature due to Collisions of Planetesimals, Greenhouse Effect of Water Vapor, Radioactive Decay raise Earth’s temperature.
⑸ 5th Formation of Magma Ocean: Rising temperature causes
the entire Earth to become a magma ocean.
⑹ 6th Formation of Core: Heavy materials like iron and nickel sink to the Earth’s core from the magma ocean.
⑺ 7th Formation of Mantle: Lighter materials like silicon and oxygen rise from the magma ocean, forming the mantle.
⑻ 8th Formation of Primitive Crust: Collisions of planetesimals decrease. Earth’s surface cools. Primitive crust forms.
⑼ 9th Formation of Primitive Seas: Water vapor in the atmosphere condenses and forms primitive oceans.
⑽ 10th Emergence of Life: First life forms arise in the oceans.
⑾ 11th Carbon Dioxide dissolves in primitive oceans, forming limestone and decreasing atmospheric carbon dioxide levels.
⑿ 12th Photosynthetic organisms appear in the oceans, increasing the amount of oxygen in the atmosphere.
4. Moon
⑴ Lunar Structure
① Maria: Dark regions on the Moon’s surface. Mostly formed by volcanic activity.
② Highlands: Bright regions on the Moon’s surface. Many craters are distributed.
③ Moon’s Size
○ Measurement 1. Using the apparent diameter of the Moon
○ Measurement 2. Using the similarity ratio of triangles
⑵ Lunar Motion
① Lunar Revolution
○ Revolution Direction: West to east or counterclockwise
○ Revolution Speed: 13° per day
② Lunar Phases
○ New Moon: Rises at sunrise, transits at noon, sets at sunset
○ 1st Phase. Waxing Crescent
○ 2nd Phase. First Quarter: Waxing Crescent
○ 3rd Phase. Waxing Gibbous: Rises at sunset, transits at midnight, sets at sunrise
○ 4th Phase. Full Moon: Rises at sunset, transits at midnight, sets at sunrise
○ 5th Phase. Waning Gibbous: Rises at midnight, transits at sunrise, sets at noon
○ 6th Phase. Third Quarter: Waning Gibbous
○ 7th Phase. Waning Crescent
⑶ Lunar Orbit
○ Sidereal Month: Time taken for the Moon to return to the same position relative to the stars. About 27.3 days.
○ Synodic Month: Time taken for the Moon to complete a full cycle of phases. About 29.5 days.
⑷ Lunar Swing-By (Gravity Assist)
① More lunar swing-bys bring the Moon closer to Earth.
⑸ Lunar Motion
① Perigee, Apogee
② Libration
③ Tidal Acceleration
⑹ Eclipse Phenomena
① Solar Eclipse
Figure 5. Progression of a Total Solar Eclipse
○ Occurs when the Moon covers the Sun.
○ Visible only in specific regions.
○ After a solar eclipse, the Sun sets before the Moon rises in the evening: due to the Moon’s orbital motion opposite to its rotation.
○ The eclipse begins with the Sun being obscured from the right side.
② Lunar Eclipse
Figure 6. Progression of a Lunar Eclipse
○ Occurs when the Earth’s shadow falls on the Moon.
○ Visible from all areas where the Moon is visible.
○ During a lunar eclipse, the Moon gets obscured from the left side.
○ (Note) During a solar eclipse, the Sun gets obscured from the right side, hence the left-to-right obscuring of the Moon during a lunar eclipse.
⑺ Origin Theories
① Differentiation Theory
② Meteorite Impact Theory
③ Outgassing Theory
5. Planets
⑴ Titius-Bode Law (1722)
① The distance from the Sun to each planet can be expressed as a simple sequence.
② The average distance between the Sun and Earth is defined as 1.
③ p = 0.4 + 0.3 × 2n (n = 0, 1, ···)
Table 1. Examples of Applying Bode’s Law (ref)
④ The cause is not yet known.
⑤ Ceres refers to the asteroid belt.
⑵ Planetary Motion
① Kepler’s First Law: Law of Elliptical Orbits
○ Definition: Planets move in elliptical orbits with the Sun at one of the foci.
○ Eccentricity
② Kepler’s Second Law: Law of Equal Areas
○ Definition: The area swept out by a line segment connecting the planet and the Sun is constant over time.
○ Principle: Conforms to the conservation of angular momentum.
③ Kepler’s Third Law: Harmonic Law
○ Definition: The square of a planet’s orbital period is proportional to the cube of the semi-major axis of its elliptical orbit.
○ Called the harmonic law due to the harmonic relationship between period and distance.
④ Vis Viva Equation
○ When the common center of mass is not considered: Using the general law of conservation of mechanical energy
○ When the common center of mass is considered
⑶ Apparent motion of planets
① Common
○ Reason planets undergo sidereal motion: Due to the difference in the planets’ orbital speeds
○ All planets undergo prograde and retrograde motion
② Apparent motion of inner planets
○ Inner planets: Mercury, Venus
○ Conjunction and opposition: Not observed
○ Maximum elongation: Approximately 30° for Mercury, approximately 45° for Venus
When observing the Sun from Earth, the Sun is located near the south, so the left represents the eastern direction, and the right represents the western direction
○ Western maximum elongation: Since the Sun is near the south and the inner planet is on the western side when observing the Sun from east to west, it is observed in the morning sky, in the eastern direction
○ Eastern maximum elongation: Since the Sun is near the south and the inner planet is on the eastern side when observing the Sun from east to west, it is observed in the evening sky, in the western direction
○ Synodic period
○ Definition: The period when the relative positions of planets with respect to Earth become the same
○ Formulation: For the planet’s orbital period P, Earth’s orbital period E, and synodic period S
○ Unlike other planets, Mercury has a synodic period shorter than a year
○ Retrograde motion: Occurs near opposition (∵ because it is close)
③ Apparent motion of outer planets
○ Outer planets: Beyond Earth’s orbit
○ Conjunction: Evening to dawn, observed for 12 hours
○ Opposition: Not observed
○ Eastern elongation: Evening to midnight, observed for 6 hours in the western sky
○ Western elongation: Midnight to dawn, observed for 6 hours in the eastern sky
○ Synodic period
○ Definition: The period when the relative positions of planets with respect to Earth become the same
○ Formulation: For the planet’s orbital period P, Earth’s orbital period E, and synodic period S
○ The synodic period of outer planets increases as they get closer to Earth and decreases as they move farther away (∵ due to increasing angular velocity difference)
Synodic period of outer planets becomes close to 1 year as they move farther from Earth
○ Outer planets have only gibbous phases
○ Retrograde motion: Outer planets retrograde with respect to opposition (∵ because it is close)
⑷ Classification of planets
Table. 2. Classification of planets
① Temperature
○ Terrestrial planets: Close to the Sun, high temperature
○ Jovian planets: Far from the Sun, low temperature
② Major constituents
○ Terrestrial planets: Light materials like methane evaporate. Heavy materials like iron, nickel, silicon condense
○ Jovian planets: Light materials not gravitationally condensed
③ Average density
○ Terrestrial planets: Composed mainly of heavy elements, high average density
○ Jovian planets: Composed mainly of light elements, low average density
④ Rotation period
○ Terrestrial planets: Composed mainly of heavy elements, slow rotation
○ Jovian planets: Composed mainly of light elements, fast rotation
⑸ Types of planets
① Mercury
○ Etymology: Named after the swift-footed messenger god
○ Orbital period: About 88 days
○ Rotation period: About 59 days
○ Radius: About 2,440 km
○ Mass: 3.3 × 10^23 kg
○ Almost no atmosphere
○ Periodical change: Shifts by 574 seconds in 100 years
○ 530 seconds: Influenced by other planets besides the Sun
○ 43 seconds: Influence of spacetime curvature by the Sun’s gravity (general relativity)
② Venus
○ Etymology: Named after the goddess of love
○ Rotation period: About 243 days
○ Radius: 0.95 times that of Earth
○ Mass: 0.82 times that of Earth
○ Atmosphere: Mostly carbon dioxide, sulfuric acid
○ Surface temperature: About 740 K (high)
○ Key feature: Appears the brightest among the planets in the solar system
③ Mars
○ Etymology: Named after the god of war
○ Reddish appearance
○ Similar in size to Mercury
○ Low gravity, almost no atmosphere
○ Atmosphere composition: 95% carbon dioxide
○ Polar caps covered with ice: Vary in size with seasons, ice primarily exists underground
○ Key features: Most impact craters, seasonal changes, volcanic eruptions
④ Jupiter
○ Etymology: Named after the king of gods
○ Largest planet in the solar system
○ Atmospheric composition: Mostly hydrogen, helium, gases
○ Great Red Spot. Dimensions: 50,000 km by 20,000 km. Located in the southern hemisphere
○ Belts: Light-colored zones
○ Zones: Dark-colored belts
○ Satellites: Over 60
○ Galilean moons: Io, Europa, Ganymede, Callisto
⑤ Saturn
○ Etymology: Named after the god of agriculture
○ Discovered to have gaps in its rings by Cassini
○ Has belts and zones similar to Jupiter but much smaller
○ Many satellites: Titan is prominent. Mostly composed of ice
○ Titan
○ Presence of water, ammonia, methane due to low temperature
○ Forms a thick atmosphere primarily composed of nitrogen
○ Origin of rings: Uncertain, theories include remnants of satellites, collision with comets, nebular hypothesis
○ Key feature: Has the largest flattening
⑥ Uranus
○ Etymology: Named after the Greek god Ouranos
○ Like Saturn, has a thin ring composed of rock fragments
○ Orbital plane is perpendicular to its rotational axis
○ Atmospheric composition: Methane, hydrogen
⑦ Neptune
○ Etymology: Named after the Roman god of the sea
○ Not visible to the naked eye
○ Atmospheric composition: Hydrogen, helium, methane, ammonia
○ Bands, zones, rings present
○ Triton: Satellite with an atmosphere
○ Discovery of Neptune
○ Initially classified as a planet: 1781, William Herschel
○ Neptune’s orbit posed a challenge to gravity theory
○ Prediction of an unknown planet: 1843, John Couch Adams
○ Discovered shortly after by German astronomers
⑧ Pluto
○ Stripped of its planetary status by the International Astronomical Union in 2006
○ Reason 1. Existence of similar bodies beyond the solar system
○ Reason 2. Small size: 2/3 the size of the Moon and shrinking
○ Reason 3. Highly elliptical orbit
6. Asteroids
⑴ Most asteroids exist in the asteroid belt between Mars and Jupiter
⑵ The total mass of all asteroids in the solar system is smaller than Earth’s mass
⑶ Asteroids revolve around the Sun in a counterclockwise direction
⑷ Asteroids are important for understanding the origin of the solar system along with comets (∵ they contain material from the early solar system)
7. Comets
⑴ Definition: Celestial bodies that orbit the Sun or a massive planet in an elliptical or parabolic orbit
⑵ Structure
① Nucleus: Dust and ice
② Coma: Atmosphere
③ Hydrogen cloud
④ Tails: Ion tail, dust tail
⑤ Ion tail always points away from the Sun’s solar wind (magnetic field)
⑶ Types: Jovian comets, Saturnian comets, Uranian comets, Neptunian comets
⑷ Period
① Short-period comets: Less than 20 years
② Halley-type comets: 20 to 200 years
③ Long-period comets: More than 200 years
⑸ Comets passing by Earth gain or lose energy
⑹ Kuiper Belt and Oort Cloud
Figure 6. Kuiper Belt and Oort Cloud
① Kuiper Belt: Region of small bodies beyond Neptune
○ Doughnut-shaped region beyond Neptune, at 30 to 50 AU
○ Mostly composed of icy asteroids
○ Home to short-period comets
② Oort Cloud: Region of dust and ice fragments beyond the solar system
○ Within 1 to 100,000 AU
○ Domain of long-period and non-periodic comets
⑺ Comets are important for understanding the origin of the solar system along with asteroids (∵ they contain material from the early solar system)
8. Meteoroids
⑴ Definition: Tiny celestial bodies that enter Earth’s atmosphere and emit light due to friction
⑵ Composition: About 30 elements including nickel, silicon, magnesium, sulfur, calcium, sodium, argon
① Meteor: Mainly composed of rock
② Meteorite: Mainly composed of iron
9. Lagrange Points
⑴ Overview
① Definition: Stable points in space where gravitational forces balance
② Discovered by Joseph Louis Lagrange in the late 18th century
⑵ Lagrange points between the Sun and Earth
Figure 7. Lagrange points between the Sun and Earth
① L1: Ideal position for observing the Sun
② L2: Ideal position for space telescopes like the James Webb Space Telescope
③ L3: Same orbit period as Earth
④ L4: Trojans exist. The asteroid 2010 TK7 is present near the L4 point
⑤ L5: Trojans exist
⑶ Lagrange points between the Sun and Jupiter
① Trojans exist at the L4 and L5 points
Input: 2019-04-07 10:00