Beyond Earth: Stars and Solar System

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Stars and Constellations Stars: Celestial bodies that shine with their own light. Constellations: Groups of stars forming patterns, often named after animals, objects, or characters. IAU Definition: International Astronomical Union (IAU) officially listed 88 constellations, dividing the entire sky into 88 regions. Navigation: Constellations helped ancient travelers and sailors find directions. Examples: Orion (The Hunter): Three bright stars form the "belt." Canis Major (Orion's Dog): Contains Sirius, the brightest star in the night sky. Taurus (The Bull): Contains Pleiades (Kṛittikā) and Aldebaran (Rohiṇī). Big Dipper (Saptaṛiṣhi): Part of Ursa Major. Little Dipper: Part of Ursa Minor, includes the Pole Star. Pole Star (Dhruva tārā): Appears stationary in the North, used for locating North direction in the Northern Hemisphere. Night Sky Watching Visibility: Best viewed from dark, open areas away from city lights, smoke, and dust (light pollution). Light Pollution: Excessive artificial light at night reducing visibility of stars. Preparation: Dark, open area, away from lights and tall structures. Choose a moonless, cloudless night. Mobile apps (Sky Map, Stellarium) can help identify objects. Allow eyes to adjust to darkness for ~30 minutes. Locating Stars/Constellations: Pole Star: Extend an imaginary line five times the distance between the two end stars of the Big Dipper's cup towards the north. Orion: Look for three bright stars in a short straight line (the belt). Best viewed Dec-Apr. Sirius: Draw an imaginary line through Orion's belt stars and extend it towards the east. Our Solar System Solar System Components: The Sun, eight planets, their moons, asteroids, and comets. Revolution: The movement of an object around the Sun. The Sun: A star, closest to Earth. Extremely hot spherical ball of gases, glows brightly. Main source of energy, heat, and light for Earth. Diameter: ~100 times that of Earth. Distance from Earth: ~150 million km (1 Astronomical Unit, au). Appears large because it's much closer than other stars. Planets: Large, nearly spherical objects revolving around the Sun. Order from Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Inner Planets (Terrestrial): Mercury, Venus, Earth, Mars. Smaller, solid surfaces with rocks. Venus: Brightest after Sun/Moon, "Morning/Evening Star." Hotter than Mercury due to atmosphere. Earth: "Blue Planet" due to water. Takes ~1 year to revolve around Sun, ~24 hours to rotate on axis. Mars: "Red Planet" due to reddish soil. Outer Planets (Gas Giants): Jupiter, Saturn, Uranus, Neptune. Much larger, mostly made of gases, flat ring structures. Dwarf Planets: Smaller objects like Pluto, redefined in 2006 by IAU. Identification: Venus is easiest to spot. Unlike stars, planets do not twinkle. Visibility: Mercury, Mars, Jupiter, Saturn also visible to naked eye. Telescopes help view dim/distant objects. Other Solar System Objects Natural Satellites (Moons): Objects that revolve around planets. Earth's Moon: Nearest neighbor, ~384,000 km away. Takes ~27 days to revolve around Earth. Quarter the size of Earth. Moon's Surface: Hardly any atmosphere, features circular bowl-like structures called craters (from asteroid impacts). India's Lunar Missions: Chandrayaan-1 (2008), Chandrayaan-2 (2019), Chandrayaan-3 (2023 - first to land near Moon's south pole). Asteroids: Small, rocky, irregular-shaped objects. Asteroid Belt: Region between Mars and Jupiter where most asteroids revolve. Sizes: 10 m to ~500 km. Comets: Visitors from outer Solar System with long tails. Made of dust, gases, rocks, and ice. Tail forms as frozen material evaporates when approaching the Sun. Appear dim away from the Sun. Example: Halley's Comet (appears every 76 years, last in 1986). Beyond the Solar System Milky Way Galaxy (Ākāśha Gaṅgā): Our home galaxy, a faint band of light seen from dark locations. Contains millions to billions of stars. Our Solar System is part of the Milky Way. The Universe: Comprises many galaxies beyond the Milky Way. Exoplanets: Planets revolving around other stars, focus of search for extraterrestrial life.