ASTRONOMY
Science
SOLAR SYSTEM
• The solar system consists of the Sun, eight planets, more than 200 moons, asteroids, comets, dust and gases.
• The Sun is the central star and accounts for more than 99% of the total mass of the solar system.
STARS AND GALAXIES
• Uneven distribution of matter and energy in the early universe led to density differences.
• Gravitational attraction caused matter to accumulate and form galaxies.
• A galaxy begins with accumulation of hydrogen gas forming a nebula.
• Localised clumps within nebulae condense to form stars.
SUN – STRUCTURE
• Solar interior: Core, Radiative Zone, Convective Zone.
• Solar atmosphere: Photosphere, Chromosphere, Corona.
• Photosphere: Bright visible surface, temperature ~6000°C.
• Chromosphere: Thin layer of burning gases, temperature ~4320°C.
• Corona: Outer plasma atmosphere, visible during total solar eclipse.
SOLAR PHENOMENA
Solar Flares:
• Magnetic storms on Sun’s surface.
• Heat corona to 10–20 million °C.
Solar Prominence:
• Arc of gas erupting from Sun’s surface.
• Held by strong magnetic fields.
Sunspots:
• Dark regions cooler than surroundings by 500–1500°C.
• Consist of umbra and penumbra.
• Related to solar activity and climate variation.
Solar Wind:
• Stream of charged particles (electrons, protons).
• Speed up to 900 km/s.
• Responsible for auroras and shape of magnetosphere.
MAGNETOSPHERE
• Region where Earth’s magnetic field deflects solar wind.
• Magnetopause is the boundary.
• Planets without strong magnetic field suffer atmospheric loss.
SOLAR CYCLE
• Periodic variation in solar activity.
• Average cycle of 11 years.
• Solar minimum: few sunspots.
• Solar maximum: high solar activity.
STELLAR MIDLIFE CRISIS
• Relationship between rotation rate and age breaks at midlife.
• Stars switch between active and low-activity modes.
PLANET FORMATION
• Gas cloud condenses → planetesimals → planets.
• Accretion leads to formation of large planetary bodies.
DWARF PLANETS
• Orbit the Sun.
• Nearly round shape.
• Have not cleared their orbital neighbourhood.
TERRESTRIAL VS JOVIAN PLANETS
Terrestrial:
• Rocky surface
• Smaller size
• Fewer moons
Jovian:
• Gaseous
• Larger size
• Many moons
KUIPER BELT
• Region beyond Neptune.
• Contains icy bodies and dwarf planets.
ULTIMA THULE
• Kuiper Belt object (2014 MU69).
• Farthest object visited by spacecraft.
MOON
• Only natural satellite of Earth.
• Formed by Giant Impact Theory.
• Same rotation and revolution period (~27 days).
MOON’S WOBBLE
• 18.6-year oscillation in lunar orbit.
• Influences tidal patterns on Earth.
LUNAR ECLIPSE
• Occurs during full moon.
• Earth comes between Sun and Moon.
• Total lunar eclipse produces red “Blood Moon”.
SUPER MOON
• Full moon at perigee.
• Appears brighter and larger.
EXOPLANETS
• Planets outside solar system.
• Detected indirectly.
• Hot Jupiters are close-in gas giants.
ASTEROIDS
• Rocky bodies between Mars and Jupiter.
• Ceres is the largest and a dwarf planet.
NEAR EARTH ASTEROIDS
• Apophis – Potentially hazardous asteroid.
• 2002 NN4 – Near Earth Object.
LIFE CYCLE OF STARS
1. Nebula
2. Protostar
3. T-Tauri Phase
4. Main Sequence
5. Red Giant
6. Red Supergiant
7. Planetary Nebula
8. White Dwarf
9. Supernova
10. Neutron Star / Black Hole
METEOROID – METEOR – METEORITE
• Meteoroid: Space rock.
• Meteor: Burning streak in atmosphere.
• Meteorite: Reaches Earth surface.
GRAVITATIONAL WAVES
• Ripples in space-time.
• Predicted by Einstein.
• Detected by LIGO.
DARK MATTER AND DARK ENERGY
• Dark Matter: Attractive force (27%).
• Dark Energy: Repulsive force (68%).
• Normal matter: 5%.
GAMMA RAY BURSTS
• Short bursts of gamma radiation.
• Associated with black hole formation.
HELIOSPHERE
• Bubble created by solar wind.
• Boundary called heliopause.
BLACK HOLES
• Gravity so strong that light cannot escape.
• Formed from massive stars.
• Event Horizon Telescope captured first image in 2019.
• Sagittarius A* is Milky Way’s black hole.
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Subject: Science
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