Chapter 12: Earth, Moon, and the Sun

Simple, mobile-friendly notes with key words in Hindi and complete chapter coverage 🌍🌙☀️

🧠 20 Most Important Words (Simple Meaning in Hindi)

सीधी, आसान हिंदी

Word	सरल अर्थ (Hindi)
Rotation	घूर्णन — अपने अक्ष पर घूमना।
Axis	धुरी — काल्पनिक रेखा जिसके चारों ओर वस्तु घूमती है।
Revolution	परिक्रमा — किसी दूसरी वस्तु के चारों ओर घूमना।
Orbit	कक्षा — परिक्रमा का रास्ता।
Hemisphere	अर्धगोला — पृथ्वी का आधा हिस्सा (उत्तरी/दक्षिणी)।
Equator	भूमध्य रेखा — पृथ्वी के बीचों-बीच की काल्पनिक रेखा।
Poles	ध्रुव — पृथ्वी के उत्तर (NP) और दक्षिण (SP) सिरे।
Sunrise	सूर्योदय — जब सूरज दिखाई देना शुरू होता है।
Sunset	सूर्यास्त — जब सूरज दिखाई देना बंद हो जाता है।
Day / Night	दिन/रात — रोशनी वाला समय/अँधेरा वाला समय।

Word	सरल अर्थ (Hindi)
Season	ऋतु — मौसम का समय (गर्मी, सर्दी आदि)।
Solstice	अयनांत — साल का सबसे लंबा/छोटा दिन।
Equinox	विषुव — दिन और रात बराबर (लगभग 12-12 घंटे)।
Tilt	झुकाव — पृथ्वी की धुरी का झुका होना।
Solar Eclipse	सूर्य ग्रहण — चंद्रमा सूर्य की रोशनी को ढक ले।
Lunar Eclipse	चंद्र ग्रहण — पृथ्वी, चंद्रमा पर सूर्य की रोशनी रोक दे।
Apparent Size	प्रतीत आकार — दूर-पास होने से दिखाई देने वाला आकार।
Constellation	नक्षत्र समूह — तारों का पहचाने जाने वाला पैटर्न।
Pole Star	ध्रुव तारा — लगभग स्थिर दिखता तारा (उत्तर दिशा)।
Big Dipper	सप्तऋषि — उत्तर आकाश का मशहूर नक्षत्र समूह।

📚 Detailed Notes (Simple English)

1) Why does the Sun seem to move? — Earth’s Rotation

The Earth rotates (spins) about its own axis once in ~24 hours.
Viewed from above the North Pole, Earth rotates anti-clockwise (from West → East).
Because we are on the rotating Earth, the Sun only appears to move East → West.
Day & Night: The half facing the Sun has day; the other half has night.
Sunrise in the East: As your place rotates into sunlight, you get sunrise; when it rotates into darkness, you get sunset.

🌟 Sky motions: Stars and the Moon also appear to move East → West due to Earth’s rotation. The Pole Star looks almost fixed; constellations (e.g., Big Dipper) seem to circle it. Long-exposure photos show star trails.

🧪 Foucault Pendulum: A very long pendulum slowly changes its swing direction relative to the floor, giving a simple proof that Earth rotates. India’s new Parliament has a 22-m Foucault pendulum.

2) Yearly changes — Earth’s Revolution

Earth also revolves around the Sun in a nearly circular orbit.
One complete revolution takes about 365 days 6 hours (~1 year).
As Earth moves, the night sky after sunset changes through the year—you see different constellations in different months.

3) Seasons — Tilt + Sphere = Seasons

Earth’s axis is tilted (not upright) and Earth is a sphere.
In June, the Northern Hemisphere tilts towards the Sun → more intense sunlight spread over smaller area + longer days ⇒ summer in the north, winter in the south.
In December, the situation reverses.
Long days at poles: Around June, the North Pole has sunlight for up to 24 hours; around December, the South Pole does.
Equator: Nearly 12 h day + 12 h night all year; seasons feel less strong near the equator. Local geography and seas also affect climate.

🗓️ Special days: Around 21 June (summer solstice, N. Hemisphere) = longest day; around 22 Dec (winter solstice) = shortest day. Around 21 Mar & 23 Sep (equinoxes) = day ≈ night everywhere.

🚫 Not because of distance! Seasons are not due to Earth being nearer or farther from the Sun. In fact, Earth is often closest to the Sun in January.

4) Solar Eclipse (Surya Grahan)

When the Moon comes between the Sun and the Earth, it can block sunlight for a small part of Earth.
Total solar eclipse: Moon’s dark inner shadow covers a small path on Earth → Sun looks fully covered for a few minutes.
Partial solar eclipse: Only part of the Sun is covered for a wider region.
Why can a small Moon cover a big Sun? Because the Moon is much closer; their apparent sizes in our sky are similar.
Planets like Venus can pass in front of the Sun but look like a tiny dot (Transit of Venus), not big enough to block it.

⚠️ Safety first: Never look at the Sun directly during an eclipse. Do not use sunglasses, binoculars or telescopes without proper solar filters. Watch at supervised public events or via safe projection methods.

📜 Ancient Indian texts like Sūrya Siddhānta gave eclipse calculations. Today, science explains eclipses clearly—no need for fear or superstitions.

5) Lunar Eclipse (Chandra Grahan)

When the Earth comes between the Sun and the Moon, Earth’s shadow falls on the Moon.
Total lunar eclipse: The Moon is fully in Earth’s shadow and can look dark red.
Partial lunar eclipse: Only part of the Moon is in shadow.
It is safe to watch a lunar eclipse with naked eyes.

🔭 India has a strong astronomy heritage—e.g., Kodaikanal Solar Observatory (since 1899). M. K. Vainu Bappu, called the father of modern Indian astronomy, led major telescope facilities.

6) Quick Connections & Activities

Shadow lengths change through the day because Earth rotates.
Find the Big Dipper on two or three times in one night—you will see it appears to move around the Pole Star.
Use a globe + torch in a dark room to see day/night and seasons by simulating tilt and revolution.

7) In a Nutshell (Super-Short Recap)

Earth rotates (≈24 h) → day & night, Sun/Moon/stars appear to move East → West.
Earth revolves (≈1 year) → night sky after sunset changes across months.
Tilt + spherical Earth → seasons, longer/shorter days, solstices, equinoxes.
Solar eclipse: Moon blocks Sun for small regions, very brief; never look directly.
Lunar eclipse: Earth’s shadow on Moon; safe to see with naked eyes.

Dates (approx.)
• 21 Mar — Spring Equinox
• 21 Jun — Summer Solstice (N)
• 23 Sep — Autumn Equinox
• 22 Dec — Winter Solstice (N)

Directions
• Earth rotates West → East
• Sun appears East → West
• Moon & stars show similar apparent motion

Safety Tip
Solar eclipse: use certified viewers or projection under expert supervision only.

Chapter 12: Earth, Moon, and the Sun — Practice Set

Neat, mobile-friendly practice in tables • Comic Sans MS • Same style as your notes 🌍🌙☀️

1) 🧩 One-Word Answer Questions (10)

Answer in one word/term
#	Question	Answer
1	The daily spinning of Earth about its axis is called?	Rotation
2	The imaginary line about which Earth spins?	Axis
3	Earth’s motion around the Sun is called?	Revolution
4	The path of Earth around the Sun?	Orbit
5	Star that appears almost fixed in the northern sky?	Pole Star
6	Recognisable pattern of stars in the sky?	Constellation
7	Day with the longest daylight in the Northern Hemisphere?	Summer solstice
8	Day and night are caused by Earth’s…?	Rotation
9	Equal day and night (about 12 hours each) is called?	Equinox
10	When the Moon blocks sunlight from reaching Earth?	Solar eclipse

2) ✍️ Fill in the Blanks (10)

Write the correct word(s)
#	Statement	Answer
1	Earth completes one rotation in about ______ hours.	24
2	Earth completes one revolution around the Sun in about ______ days and ______ hours.	365 days; ~6 hours
3	Earth rotates from ______ to ______.	West; East
4	At the Equator, day and night are almost ______ hours each.	12
5	In June, the Northern Hemisphere is tilted ______ the Sun.	towards
6	The apparent daily motion of the Sun is due to Earth’s ______.	rotation
7	The Moon appearing as a tiny dot crossing the Sun is called the Transit of ______.	Venus (when Venus transits)
8	The line dividing Earth into Northern and Southern Hemispheres is the ______.	Equator
9	On about 21 March and 23 September, day and night are nearly equal; these days are called ______.	equinoxes
10	When Earth blocks sunlight from reaching the Moon, it is a ______ eclipse.	lunar

3) ✅❌ True/False with Explanation (10)

Mark True (T) / False (F) and read why
#	Statement	T/F	Why?
1	Day and night are caused by Earth’s revolution around the Sun.	False	They are caused by Earth’s rotation on its axis.
2	Earth rotates from East to West.	False	It rotates from West to East; hence the Sun appears to move East → West.
3	In December, the Northern Hemisphere has shorter days than the Southern Hemisphere.	True	Northern Hemisphere tilts away from the Sun in December.
4	We can safely watch a solar eclipse with the naked eye.	False	Direct viewing can damage eyes; use safe, supervised methods only.
5	The Pole Star appears nearly stationary in the sky.	True	Earth’s axis points close to it; other stars seem to circle around it.
6	Seasons occur mainly because Earth is sometimes much closer to the Sun.	False	Seasons are due to Earth’s tilted axis and spherical shape, not distance.
7	Constellations visible at sunset stay the same through the year.	False	As Earth revolves, we face different parts of the sky after sunset.
8	Earth completes one rotation in about 24 hours.	True	That is the length of a day (approximately).
9	Lunar eclipse happens when the Moon comes between the Sun and Earth.	False	That alignment causes a solar eclipse; lunar eclipse is when Earth is in between.
10	The Moon looks bigger than the Sun; that’s why it covers the Sun.	False	Its apparent size matches the Sun’s because it is much closer, not bigger.

4) ✨ Very Short Answers (2–3 lines each) — (10)

Answer briefly in 2–3 lines
#	Question	Answer (2–3 lines)
1	Why does sunrise happen earlier in the east of India than in the west?	Earth rotates West → East. Places in the east turn into sunlight first, so sunrise occurs earlier there.
2	What is the role of Earth’s tilt in causing seasons?	The tilted axis makes one hemisphere face the Sun more (longer days, higher Sun) while the other faces away, creating opposite seasons.
3	Why do constellations after sunset change over the year?	As Earth revolves, our night side points toward different regions of space in different months. Hence visible patterns change.
4	Define solstice and give one date.	Solstice: day with maximum or minimum daylight. In the North, around 21 June = longest day; around 22 Dec = shortest day.
5	What is an equinox?	On equinoxes (≈21 Mar, 23 Sep) day and night are nearly equal (about 12 hours each) everywhere on Earth.
6	Why is it unsafe to view a solar eclipse directly?	The Sun’s intense light can permanently harm the eyes even when partly covered. Use safe projection or certified filters under supervision.
7	Why can the Moon cover the Sun during a total solar eclipse?	Although smaller, the Moon is much closer; its apparent size matches the Sun’s from Earth, so it can block the Sun briefly.
8	Why are seasons less extreme near the Equator?	Day length stays close to 12 hours all year and the Sun’s path changes little, so seasonal contrast is mild.
9	What does a Foucault pendulum demonstrate?	It provides a simple demonstration that Earth rotates; the swing plane appears to slowly turn relative to the ground.
10	Why can a lunar eclipse be seen from a large area?	Earth’s shadow on the Moon is visible from the entire night side of Earth, so many regions can watch it simultaneously.

5) 🧠 Short Answers (3–4 lines each) — (10)

Answer in 3–4 lines
#	Question	Answer (3–4 lines)
1	Explain day–night with a globe and a torch.	Shine a torch on the globe: the lit half has day; the dark half has night. As you rotate the globe West → East, a place moves from darkness into light (sunrise), across daylight (noon), and back into darkness (sunset).
2	Why are June days longer in the Northern Hemisphere?	In June the Northern Hemisphere tilts toward the Sun. Sun’s rays are more direct and the Sun stays above the horizon for longer, giving longer days and warmer weather (summer).
3	Differentiate solar and lunar eclipses (positions, visibility, safety).	Solar: Sun–Moon–Earth (Moon between Sun & Earth); visible along a narrow path; never view directly. Lunar: Sun–Earth–Moon (Earth between Sun & Moon); visible from most of Earth’s night side; safe to view.
4	Why do stars appear to circle the Pole Star?	Earth’s axis points near the Pole Star, so as Earth rotates, the sky seems to turn around that fixed point. Hence stars trace circles (star trails) around the Pole Star.
5	Why is a total solar eclipse brief and narrow in path?	The Moon’s umbral shadow on Earth is small, and both Earth’s rotation and the Moon’s orbital motion make the shadow race across Earth. Totality typically lasts only a few minutes at any one place.
6	How does “apparent size” let the Moon cover the Sun?	Angular size = physical size + distance. Though the Sun is huge, it’s far away. The Moon is small but much closer. From Earth, both appear nearly the same size, allowing total coverage.
7	Define solstice and equinox with dates for the North.	Solstices: ~21 Jun (longest day), ~22 Dec (shortest day). Equinoxes: ~21 Mar and ~23 Sep when day ≈ night. They result from Earth’s tilt and revolution.
8	How does revolution change the night sky through months?	Each evening after sunset, Earth’s night side faces a slightly different direction in space as we orbit the Sun. Therefore, constellations rising at sunset change with the months.
9	Why is it winter in India when it is summer in Australia?	India is in the Northern Hemisphere; Australia is in the Southern. When the north tilts toward the Sun (June), it’s summer there and winter in the south—and the reverse in December.
10	List two safe ways to observe a solar eclipse.	Attend a supervised public event (planetarium/astronomy club) using certified solar viewers, or use indirect projection methods (pinhole/card or mirror projection) under expert guidance.

12. Earth, Moon, and the Sun