South 고등학교 2학년 Planetary and Space Science
Chapters: 3
1. Space exploration and planetary systems
Findings of solar-system probes · Space weather and near-Earth objects · Gravity and orbits in the solar system · Planets and small bodies · Detecting exoplanets
- Space Exploration – Space exploration means sending rockets, satellites, probes and people beyond Earth's air. Rockets rise by pushing gas down (action–reaction). At about 7.9 km/s sideways a craft keeps falling around Earth in orbit; at 11.2 km/s it escapes. Since 1957 space has been a place of rivalry and cooperation, and it gives us weather forecasts, navigation, communication and new science.
- Kepler's Laws of Planetary Motion – Kepler gave three rules for how planets move. 1) Each planet moves on an ellipse with the Sun at one focus. 2) The line from the Sun to the planet sweeps equal areas in equal times, so the planet moves faster when it is near the Sun. 3) The square of the time for one round (T²) is proportional to the cube of the semi-major axis (a³). The second law is really conservation of angular momentum. The third law follows from Newton's law of gravitation.
- The Solar System – The Solar System is the Sun and everything its gravity holds: 8 planets, their moons, dwarf planets, asteroids, comets and dust. The inner four planets (Mercury, Venus, Earth, Mars) are small and rocky. After the asteroid belt come the giants: gas giants Jupiter and Saturn, ice giants Uranus and Neptune. Gravity pulls planets towards the Sun while they move sideways, so they travel in orbits; closer planets move faster and have shorter years. It all formed about 4.6 billion years ago from a spinning cloud of gas and dust.
- Exoplanets: How Do We Find Planets Around Other Stars? – An exoplanet is a planet that goes round a star other than the Sun. Planets are tiny and dim next to a star, so we mostly find them by clues. In the transit method, a planet crosses in front of its star and the star's light dips by about (planet size / star size) squared. In the radial velocity (wobble) method, the planet's pull makes the star move in a tiny circle, and its light shifts blue and red. The time between dips or wobbles gives the planet's year. Other methods are direct imaging and microlensing. More than 5,000 exoplanets are known.
2. Observing the Sun and stars
Solar phenomena · Distances from parallax and brightness · Space velocity of stars · Stellar masses from binaries · Variable stars
- The Sun: Our Star from Core to Corona – The Sun is a star: a huge ball of hot gas (plasma), about 73% hydrogen and 25% helium by mass. It is 1.39 million km wide (109 Earths), holds 99.86% of the Solar System's mass and is about 150 million km away, so its light takes about 8 minutes 20 seconds to reach us. Its surface (photosphere) is about 5500 °C; its core is about 15 million °C. In the core, nuclear fusion joins 4 hydrogen nuclei into 1 helium nucleus; the small mass lost becomes energy (E = mc²). The Sun turns about 4 million tonnes of mass into energy every second. Energy crawls out through the radiative zone (as light, over thousands of years), then rises by convection to the surface. Fusion also makes neutrinos, tiny particles that escape at once and prove fusion is happening. The Sun's magnetic field makes sunspots (cooler, darker patches), flares (sudden blasts) and coronal mass ejections. Activity rises and falls in an 11-year cycle. The solar wind and storms cause auroras and can disturb radio, GPS, satellites and power grids.
3. Galaxies and the universe
Cluster ages from colour-magnitude diagrams · Interstellar dust · Rotation curves and dark matter · Redshift of galaxies · Large-scale structure
- Star Clusters: Open, Globular and How We Find Their Age – A star cluster is a group of stars born together from one gas cloud, so they share the same age and almost the same chemical make-up. Open clusters are loose, young and blue; globular clusters are dense, old and reddish. Plot each star's brightness against its colour and you get a main-sequence curve; the point where it bends away (the turn-off) tells the cluster's age: lower turn-off means older cluster.
- The Interstellar Medium: Gas, Dust and Molecules Between the Stars – The interstellar medium (ISM) is the thin gas and dust that fills the space between stars. About 99% of it is gas (mostly hydrogen and helium) and about 1% is tiny solid dust grains. In cold, dense clouds atoms join into molecules such as H₂ and CO. Dust absorbs and scatters starlight, blue light more than red, so a star behind dust looks fainter (extinction) and redder (reddening).
- Dark Matter: The Invisible Mass Holding Galaxies Together – Stars far from a galaxy's centre orbit about as fast as stars near it. If only the visible matter pulled on them, far stars should move slowly. This flat rotation curve means there is extra, invisible mass: dark matter. It does not shine or block light, but its gravity is real. Today's best picture of the cosmos is about 5% ordinary matter, 27% dark matter and 68% dark energy, which makes the expansion speed up.
- Cosmology: The Expanding Universe and the Big Bang – Cosmology is the study of the whole universe: its structure, history and future. Galaxies gather in groups, clusters and filaments around huge voids. Distant galaxies are moving away from us, faster the farther they are (Hubble's law, v = H₀d), because space itself is expanding. Running the expansion backwards leads to a hot, dense beginning about 13.8 billion years ago, the Big Bang. The main evidence is redshift, the cosmic microwave background and the amounts of hydrogen and helium. Most of the universe is dark matter and dark energy.