🌍 Class 7 Science – Chapter 12: Earth, Moon and Sun

🚴‍♀️ Rashmika’s Observation
•  One morning in Kanniyakumari, Tamil Nadu, 12-year-old Rashmika was cycling to school with excitement.
•  Her science class that day was special because students would share their own interesting observations. 🌟

🌴 Changing Shadows
•  On her way, she noticed something unusual about a coconut tree’s shadow.
•  The shadow was long in the morning 🌅 and short in the afternoon ☀️.
•  She wondered why this happened.

🌞 What Is Really Moving?
•  Rashmika thought the shadow changed because the Sun moved across the sky.
•  But she also remembered learning in Class 6 that the Earth moves around the Sun. 🌍✨
•  This made her confused. If Earth moves around the Sun, then…

🤔 Her Question
•  Does the Sun really move in the sky, or is it the Earth’s movement that makes it look that way?

🌍 12.1 Rotation of the Earth

🌅 Why does the Sun rise in the East and set in the West?
•  We all see the Sun rising in the East and setting in the West every day.
•  But why does this happen? Let's understand it with a fun activity.

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🌞 Does the Sun really move?
•  When we look from Earth, the Sun appears to rise in the East and travel to the West.
•  But the Sun is not actually moving across the sky.
•  It appears to move because the Earth is rotating on its own axis.
•  Just like a spinning top 🌀, a rotating fan 🧭, or a spinning ball 🏀, the Earth also spins.

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🌎 How does the Earth Rotate?

•  The Earth rotates on its axis, an imaginary line passing through the North Pole and South Pole.
•  It completes one full rotation in about 24 hours.
•  When viewed from above the North Pole, the Earth rotates anti-clockwise.
•  This means it rotates from West to East.
•  Because of this rotation, the Sun appears to move from East to West.

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🌅➡️🌌 Day and Night Cycle
•  The side of Earth facing the Sun has daytime.
•  The opposite side has night.
•  As Earth rotates, every place moves through day → evening → night → morning, again and again.

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👧 Understanding it from the Equator

Imagine you are standing on the Equator and Earth rotates:
1.  Morning:
o  You see the Sun on your right side in the East.
2.  Noon:
o  As Earth rotates, the Sun appears over your head.
3.  Evening:
o  The Sun moves towards the West and slowly disappears.
o  Stars begin to appear as the sky becomes dark. 🌃
👉 All of this happens because Earth rotates from West to East.

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🌌 Do Stars Move in the Sky?

•  If the Earth is rotating, you might wonder:
Shouldn’t the stars also appear to move just like the Sun?
•  Let’s explore this by observing the night sky.

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⭐ Why does this happen?
•  The axis of the Earth points almost exactly toward the Pole Star.
•  Because of this, the Pole Star looks almost still in the sky.
•  Other stars appear to move around it as the Earth rotates.

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🌙 What about the Moon?
•  Just like the Sun, the Moon also appears to rise in the East 🌅
and set in the West 🌇.
•  This is because the Earth rotates from West to East.

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🌍 12.2 Revolution of the Earth

•  While the Earth spins on its axis, it also revolves around the Sun.
•  Rotation = spinning on its own axis.
•  Revolution = moving around another object.
•  The Earth moves around the Sun in a path called its orbit.
•  When viewed from the top, this orbit is nearly circular.
•  One full revolution takes about 365 days and 6 hours. 🌞🌍

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🌌 12.2.1 Changing view of night sky from the Earth

•  Every evening, once the Sun sets, the night sky becomes visible.
•  Because the Earth is rotating, we see the sky after sunset.
•  But since the Earth is also revolving around the Sun, our view of the stars changes slowly through the year.

⭐ What we observe:
•  Different months show different stars at sunset (Fig.).

•  If you observe a star pattern at the same time each night, a month apart, you will notice a small shift.
•  Over several months, completely different star groups appear in the sky.
👉 This happens because as the Earth moves around the Sun, we face different directions in space at night.

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🌞 12.2.2 Seasons on the Earth

A common question:
•  Why do we have summer, winter, spring, and autumn every year?
•  Why are summer days longer than winter days?

🌏 Reason:
The Earth’s axis is tilted, not straight.
This tilt does not change as the Earth revolves around the Sun.

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🌞 June: Northern Hemisphere's Summer
(Refer to Fig. 12.9, 12.10a, 12.11a)

•  In June, the Northern Hemisphere is tilted towards the Sun.
•  Sunlight falls more directly because the rays cover a smaller area, so the heating is stronger. ☀️
•  This hemisphere also receives more than 12 hours of sunlight each day.
•  Result: Summer in the Northern Hemisphere.
At the same time:
•  The Southern Hemisphere is tilted away from the Sun.
•  Sunlight is spread over a larger area, so it is less intense.
•  It receives less daylight.
•  Result: Winter in the Southern Hemisphere.

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❄️ December: Northern Hemisphere's Winter
(Refer to Fig. 12.10b and 12.11b)
•  In December, the Northern Hemisphere is tilted away from the Sun.
•  Sunlight becomes less intense, spread over a larger area.
•  It also receives less than 12 hours of daylight.
•  Result: Winter.
Meanwhile:
•  The Southern Hemisphere is tilted towards the Sun.
•  It has summer in December.

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🌐 What about the Equator?
•  At the equator, there are always about 12 hours of day and 12 hours of night.
•  The intensity of sunlight does not change much throughout the year.
•  So places near the equator (like southern India) do not feel sharp seasonal changes.
Local features like mountains, forests, and nearby oceans also affect how hot or cold a place feels.

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🌑 12.3 Eclipses

•  Day and night, seasons, and life on Earth depend on the Sun.
•  But can sunlight ever get blocked before reaching Earth?
•  Mercury and Venus lie between the Sun and Earth, but they appear very small and cannot block the Sun completely.
•  But the Moon can! 🌙
•  The Moon is Earth’s natural satellite and revolves around Earth while Earth revolves around the Sun.

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🌘 12.3.1 Solar Eclipse

•  Sometimes the Moon comes between the Sun and the Earth.
•  When this blocks sunlight from reaching us, it is called a solar eclipse.

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🌑 How a Solar Eclipse Happens

•  When the Moon blocks sunlight, its shadow falls on a small part of Earth.
•  People standing in that darkest region see a total solar eclipse.
•  People standing in the lighter shadow see a partial solar eclipse.

⭐ Total Solar Eclipse
•  The Moon covers the Sun completely.
•  It becomes dark during the day for a few minutes.

⭐ Partial Solar Eclipse
•  Only part of the Sun is covered by the Moon.
•  Because Earth rotates and the Moon moves in its orbit, the Moon's shadow moves across Earth.
•  That’s why a total eclipse at a place lasts only a few minutes.

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👀 Safe Viewing of a Solar Eclipse
⚠ Never look at the Sun directly, even during an eclipse.
•  It can damage the eyes and cause permanent blindness.
•  Do not use:
o  Sunglasses
o  Binoculars
o  Telescopes
The safe way:
•  Visit eclipse-viewing events organised by planetariums or astronomy clubs.
•  They provide:
o  Special eclipse-viewing glasses
o  Proper scientific explanations
o  A safe observing environment

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🕰️ Eclipses in Ancient Times
•  People have recorded eclipses since ancient days.
•  When the reasons were unknown, they found them frightening.
•  Many superstitions developed, such as:
o  Not eating
o  Not cooking
o  Staying indoors
Now we know eclipses are natural and harmless, as long as we don’t look at the Sun directly.
Scientists actually travel around the world to observe eclipses because they help study special solar phenomena.

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🌕 12.3.2 Lunar Eclipse

•  As the Moon revolves around the Earth, there are times when the Earth comes between the Sun and the Moon.
•  When this happens, the Earth blocks sunlight from reaching the Moon.
•  This event is called a lunar eclipse. 🌑
•  On such nights, we see the Earth’s shadow falling on the bright full Moon.
•  Given shows how the Sun, Earth, and Moon line up during a lunar eclipse.

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🌑 Total Lunar Eclipse
•  When the entire Moon is inside Earth’s shadow, it is called a total lunar eclipse.
•  The Moon does not disappear completely.
•  Instead, it turns a dark red colour, often called the “Blood Moon”.
•  The Moon remains red until it moves out of Earth’s shadow.

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🌘 Partial Lunar Eclipse
•  When only part of the Moon enters Earth’s shadow, and the remaining part stays bright, it is called a partial lunar eclipse.

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👀 Safe to Watch
•  Unlike a solar eclipse, a lunar eclipse is completely safe to look at.
•  You can watch the red or shadowed Moon with your naked eyes without any risk. 🌕