solar system

Geocentric: Earth-centered model; all celestial bodies, including the moon, planets, and stars, revolve around Earth, a belief held since ancient times, notably by Ptolemy.
Heliocentric: Sun-centered model; proposed by Nicolaus Copernicus in the 16th century, suggesting that planets, including Earth, revolve around the Sun, leading to a significant paradigm shift in understanding the cosmos.

The Sun comprises about 99.85% of the solar system mass, primarily made up of hydrogen (about 74%) and helium (about 24%), with trace amounts of heavier elements such as oxygen, carbon, neon, and iron.
Stars' composition evolves over their lifecycle; hydrogen fuses into heavier elements such as helium, carbon, and oxygen in stellar cores during various phases of the star's lifecycle.
Sun's core temperature reaches up to $10^7$ Kelvin; significantly hotter than Earth’s core temperature of approximately 6000 Kelvin.
The Sun's structure includes:
- Radiative Zone: Inner layer where energy is transported outwards through radiation, composed of dense hydrogen.
- Convective Zone: Outer layer with gas movement; hot gas rises, cools, and descends, creating convection currents.
- Photosphere: Visible surface of the Sun, responsible for emitting light.
- Chromosphere: Layer above the Photosphere, often observed during solar eclipses as a red halo.
- Corona: Outermost atmosphere of the Sun, extending millions of kilometers into space, observable as a white halo during solar eclipses.

Sunspots: Cooler, darker areas on the Sun's surface caused by magnetic activity, which follow an 11-year solar cycle, influencing solar radiation and climate on Earth.
Solar flares: Bursts of radiation that erupt from the Sun's surface; these flares can impact satellite communication and power grids on Earth.
Prominences: Large, bright loops of gas that form in the corona, sometimes being ejected back to the Sun’s surface.

Inner (Terrestrial) Planets: Mercury, Venus, Earth, Mars; characterized by rocky compositions, dense metallic cores, and thin atmospheres, suitable for geological activity.
Outer (Jovian) Planets: Jupiter, Saturn, Uranus, Neptune; composed primarily of gases with thick atmospheres dominated by hydrogen and helium, featuring extensive moon systems and ring structures.

Inner Planets: Have rocky crusts and dense cores; separated from outer planets by the asteroid belt, indicating different formation processes.
Outer Planets: Much less dense than terrestrial planets, mainly consisting of gaseous hydrogen and helium with significant atmospheric pressure; all have ring systems and numerous moons. Gravitational force of a planet heavily influences its atmosphere retention, with larger planets better at holding lighter gases.

Formed from a nebula: a large cloud of gas and dust, predominantly composed of hydrogen and helium, leading to the initial formation of the Sun and surrounding planetary bodies.
The planetary formation theory includes the accretion of particles that coalesce in a rotating disk around the forming Sun, leading to the creation of planets, moons, asteroids, and comets.

Mercury: Smallest planet, heavily cratered, with a weak atmosphere (0.38 Earth gravity) resulting from low gravity and high temperatures, leading to minimal atmospheric retention.
Venus: Almost the same size as Earth; features a thick carbon dioxide atmosphere, causing a greenhouse effect that leads to extreme surface temperatures (up to 475°C) and pressure 92 times that of Earth.
Mars: Has a thin atmosphere (40% CO2); possesses two small moons (Phobos, Deimos); notable surface features include ice caps and indications of past water flow.
Jupiter: Largest planet in the solar system, with a strong magnetic field, dozens of moons (including the largest moon Ganymede), and a thick atmosphere composed mostly of hydrogen and helium (2.9 Earth gravity).
Saturn: Known for its extensive and visually stunning ring system, composed of ice and rock particles; its overall density is less than that of water, which would cause it to float if placed in a large enough body of water.
Uranus: Unique for its tilted axis, which makes it rotate on its side; has a frigid atmosphere primarily consisting of methane gas, giving it a blue color.
Neptune: Notable for the strongest winds in the solar system and dynamic storm systems, with a high gravity (1.4 Earth gravity) that influences its atmospheric conditions.

Pluto: No longer considered a planet; classified as a dwarf planet located in the Kuiper Belt. It is smaller than Earth’s moon and has five known moons, with Charon being the largest and closest to Pluto.

Comets: Composed of ice, dust, and rocky material; they develop comas (a glowing envelope) and tails when they approach the Sun due to sublimation of their icy components.
Asteroids: Solid rocky masses primarily found in the asteroid belt between Mars and Jupiter, can range in size from tiny boulders to dwarf planets.
Meteoroids: Small fragments of asteroids or comets; meteors are the visible streaks in the sky when meteoroids enter Earth's atmosphere, while meteorites are those fragments that land on Earth.

Impact craters: Formed by meteor strikes; notable examples like Barringer Crater (Arizona) and Vredefort Crater (South Africa) offer critical insights into Earth's geological history and impact events over time.