Ch 17 takes students on a journey through the solar system — the moon, planets, asteroids, comets, meteors, and beyond. Students also learn about constellations and our galaxy.
Moon: Earth's natural satellite, no light of its own (reflects sunlight), phases change in ~29.5 days (new moon → waxing → full moon → waning). 8 planets in order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Inner planets are rocky; outer planets are gas/ice giants.
Asteroids: rocky bodies between Mars and Jupiter (asteroid belt). Comets: icy bodies that develop a tail when near the sun. Meteors: streaks of light when meteoroids burn in atmosphere ("shooting stars"). Meteorites: meteors that survive and reach Earth. Artificial satellites: man-made, orbit for communication, weather, etc.
Stars are self-luminous (produce light by nuclear fusion). Constellations are patterns of stars (Ursa Major/Big Dipper, Orion). Pole Star (Polaris) indicates north. Our solar system is part of the Milky Way galaxy, which contains billions of stars.
Download: https://ncert.nic.in/textbook/pdf/hesc117.pdf | Complete book: https://ncert.nic.in/textbook/pdf/hesc1ps.zip
In 2006, the International Astronomical Union (IAU) reclassified Pluto as a "dwarf planet" because it has not cleared the neighbourhood around its orbit — there are many similar-sized objects in the Kuiper Belt near its path. Planets must: orbit the sun, have sufficient mass for a round shape, and have cleared their orbit.
Book a Trial + Diagnostic session. Get a personalized Learning Path with clear milestones, tutor match, and a plan recommendation — all within 24 hours.
Book Trial + Diagnostic →