Earth, Moon, and the Sun

About this chapter

Earth, Moon, and the Sun is Chapter 12 of Class 7 Curiosity. Through 12-year-old Rashmika of Kanniyakumari, Tamil Nadu — puzzled by morning-versus-afternoon coconut shadows and unsure whether the Sun moves or the Earth moves — the chapter answers the apparent motion of the sky. It builds these core ideas: rotation of the Earth, a spinning motion on its own axis that passes through the geographic North and South Poles, completed in about 24 hours in an anti-clockwise direction from West to East as viewed from above the North Pole; the merry-go-round and globe-with-torch activities (Activities 12.1, 12.2) that explain why the Sun appears to rise in the East and set in the West and why sunrise reaches the eastern parts of India first; Aryabhata's fifth-century Aryabhatiya verse and the value of 23 hours 56 minutes 4.1 seconds for one rotation; Leon Foucault's 1851 pendulum and the 22-metre Foucault pendulum hung in the Constitution Hall of the new Parliament building, New Delhi; revolution of the Earth around the Sun in nearly one year (365 days 6 hours) along a nearly circular orbit; why different stars rise at sunset in different months (Fig. 12.8) and the Bhil and Pawara monsoon-marker patterns of the Tapi Valley; the tilt of the Earth's axis and the spherical shape together causing seasons — summer when a hemisphere is tilted toward the Sun, winter when tilted away — and not the slight elliptical-orbit distance (Earth is closest in January); the summer solstice (~21 June, longest day in the Northern Hemisphere), winter solstice (~22 December, shortest day), spring and autumn equinoxes (~21 March, 23 September, 12-hour day and night), and the six-month sunshine then six-month darkness at the North and South Poles; the equator's constant 12-hour day and the weaker seasonal effect in southern India; solar eclipse — apparent size of the Moon and Sun being similar from Earth, the Moon's shadow falling on a small region producing a total solar eclipse, surrounding regions seeing a partial solar eclipse, the strict ban on viewing the Sun directly or through sunglasses, binoculars or telescopes during an eclipse, and safe public viewing through planetaria; lunar eclipse — the Earth coming between the Sun and Moon, the full Moon turning dark red in a total lunar eclipse, partial lunar eclipse when only part of the Moon enters the Earth's shadow, and the safe naked-eye viewing of lunar eclipses; the Sanskrit word grahan, the Surya Siddhanta, the Kodaikanal Solar Observatory of 1899 in the Palani Hills and the Indian Institute of Astrophysics (IIA), Bengaluru; and M.K. Vainu Bappu, the father of modern Indian astronomy. CTET Paper 2 Science tests this chapter through assertion-reasoning on tilt-vs-distance, ordering of solstices and equinoxes, eclipse-safety, partial-vs-total geometry, sunrise-earlier-in-Gujarat-or-Jharkhand reasoning, and ISRO-Indian context items. The four tests — Practice 15, Quiz 15, Hard 15, Mastery 30 — cover these ideas at exam depth.