Solar System
Geography · सौर मंडल
📋Quick Overview
The Solar System consists of the Sun, 8 planets, dwarf planets, asteroids, comets, and other celestial bodies. The Sun is at the center and all planets revolve around it. The order of planets from the Sun is: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Pluto was demoted to a dwarf planet in 2006 by the International Astronomical Union (IAU).
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A Light Year is the distance light travels in one year = 9.461 x 10^12 km. It is a unit of DISTANCE, not time.
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The Sun is a medium-sized star made of Hydrogen (73%) and Helium (25%). Its surface temperature is about 5,778 K and core temperature is about 15 million degree Celsius.
📖8 Planets — Key Facts Table
| Planet | Position | Key Fact | Moons |
|---|---|---|---|
| Mercury (बुध) | 1st | Smallest planet, closest to Sun, no moon, no atmosphere | 0 |
| Venus (शुक्र) | 2nd | Hottest planet, brightest planet, Earth's twin (similar size), rotates clockwise (east to west), slowest rotation | 0 |
| Earth (पृथ्वी) | 3rd | Only planet with life, 'Blue Planet', 1 moon, 71% water | 1 |
| Mars (मंगल) | 4th | Red Planet (iron oxide), 2 moons (Phobos & Deimos), highest mountain Olympus Mons | 2 |
| Jupiter (बृहस्पति) | 5th | Largest planet, fastest rotation (10 hrs), Great Red Spot (storm), most massive | 95 |
| Saturn (शनि) | 6th | Famous for rings, 2nd largest, least dense (can float on water), most moons (146) | 146 |
| Uranus (अरुण) | 7th | Rotates on its side (tilted 98°), also rotates clockwise like Venus, 'Ice Giant', discovered by William Herschel (1781) | 28 |
| Neptune (वरुण) | 8th | Coldest planet, farthest from Sun, strongest winds, discovered by mathematical prediction (1846) | 16 |
📝Sun & Moon — Key Facts
- •Sun's age: about 4.6 billion years. It is a Yellow Dwarf star.
- •Sun's light reaches Earth in about 8 minutes 20 seconds
- •The outermost layer of the Sun visible during a total solar eclipse is called Corona
- •Moon is Earth's only natural satellite. It takes 27.3 days to orbit Earth (sidereal period)
- •Moon has no atmosphere, no water (small traces found), no light of its own — reflects sunlight
- •Neil Armstrong was the first person to walk on the Moon (Apollo 11, July 20, 1969)
- •Highest point on Moon: Mons Huygens. Moon's gravity is 1/6th of Earth's
📝Planet Records — Who is What?
| Record | Planet |
|---|---|
| Largest planet | Jupiter |
| Smallest planet | Mercury |
| Hottest planet | Venus (not Mercury!) |
| Coldest planet | Neptune |
| Fastest rotation | Jupiter (~10 hours) |
| Slowest rotation | Venus (243 Earth days) |
| Most moons | Saturn (146) |
| Brightest planet | Venus (Morning/Evening Star) |
| Earth's twin | Venus (similar size) |
| Red Planet | Mars |
| Planet with rings | Saturn (most prominent) |
| Least dense planet | Saturn |
📝Dwarf Planets, Asteroids & Comets
- •Dwarf Planets: Pluto (demoted 2006), Ceres, Eris, Haumea, Makemake
- •Pluto was discovered by Clyde Tombaugh in 1930. It has 5 moons; largest is Charon.
- •Asteroids are rocky bodies found mainly in the Asteroid Belt between Mars and Jupiter
- •Ceres is the largest asteroid. It is also classified as a dwarf planet.
- •Comets are made of ice, dust, and gas. They develop a tail when near the Sun. Halley's Comet appears every 76 years (next: 2061).