Class 6 — Chapter 12: Beyond Earth

12.1 Stars and Constellations

Stars: Celestial bodies that shine with their own light. The Sun is the closest star to Earth.
Constellation: Historically, groups of stars forming recognizable patterns. Currently, they refer to 88 officially defined regions of the sky established by the International Astronomical Union (IAU).
Orion: Represented as a hunter. Its middle three stars represent the belt.
Canis Major: Represents the hunter's dog and contains Sirius, the brightest star in the night sky.
Taurus: Represents a bull battling Orion.

Nakṣhatra: Indian astronomical term used to denote a specific star or group of stars.
Ārdrā: The star Betelgeuse in the Orion constellation.
Kṛittikā: The Pleiades star cluster in the Taurus constellation.
Rohiṇī: The star Aldebaran in the Taurus constellation.

Big Dipper: Part of the Ursa Major constellation (known as Saptaṛiṣhi in India).
Little Dipper: Part of the Ursa Minor constellation.
Pole Star (Polaris): Known as Dhruva tārā in India. It lies in the Little Dipper and remains nearly stationary in the North, serving as a vital navigation tool in the Northern hemisphere.

12.2 Night Sky Watching

Light Pollution: Excessive artificial light at night that reduces the visibility of celestial objects.
Dark Sky Reserves: Protected areas established to control light pollution for research and stargazing (e.g., Hanle Dark Sky Reserve in Ladakh, India).
Sky Mapping Apps: Digital tools like Stellarium and Sky Map used to identify stars, planets, and constellations.
Telescope: An optical instrument used to view distant celestial objects brighter and larger.

12.3 Our Solar System

The Sun: An extremely hot spherical ball of gases and the primary source of energy for Earth. Its diameter is about 100 times that of Earth.
Astronomical Unit (au): The average distance between the Sun and the Earth (approximately 150 million km).
Proxima Centauri: The nearest star to Earth after the Sun, located at a distance of about 269,000 au.

Planet: A large, nearly spherical object that revolves around a star.
Revolution: The orbital movement of a planet around the Sun. Earth takes nearly one year to complete one revolution.
Rotation: The spinning of a planet on its own axis. Earth takes 24 hours for one full rotation.
Inner Planets: Mercury (Budha), Venus (Śhukra), Earth (Pṛithvī), and Mars (Mangala). They are smaller, rocky, and have solid surfaces.
Outer Planets: Jupiter (Bṛihaspati), Saturn (Śhani), Uranus, and Neptune. They are larger gas/ice giants with ring systems.
Dwarf Planet: Smaller celestial bodies like Pluto, which was reclassified from a planet to a dwarf planet by the IAU in 2006.

Satellite: Any object that moves around a much larger object. Moons are natural satellites of planets.
The Moon: Earth's only natural satellite, located about 3,84,000 km away. It takes about 27 days to revolve around Earth. Its surface is covered with circular bowl-like craters caused by asteroid impacts.
Chandrayaan Missions: India's lunar exploration program. Chandrayaan-3 successfully soft-landed near the Moon's south pole on August 23, 2023, which is celebrated as National Space Day in India.

Asteroids: Small, rocky, irregularly shaped objects revolving around the Sun, mostly in the Asteroid Belt between Mars and Jupiter.
Comets: Icy-rocky visitors from the outer solar system made of dust, gases, rocks, and ice. They develop long, glowing tails of evaporating material as they approach the Sun.
Halley's Comet: A famous comet that appears every 76 years (last seen in 1986).

12.4 The Milky Way Galaxy and the Universe

Milky Way Galaxy (Ākāśha Gangā): Our home galaxy, containing millions to billions of stars, including our Solar System. It appears as a faint band of light across a dark, clear night sky.
The Universe: The vast expanse containing all matter, energy, galaxies, and stars.
Exoplanets: Planets discovered revolving around stars outside our Solar System.

Science: Class 6 — Chapter 12: Beyond Earth