🌍 Chapter Introduction
The Earth is part of a vast system of planets, moons and other celestial objects. Among the objects closest and most important to us are the Earth, the Moon and the Sun.
The Sun provides most of the energy that supports life on Earth. The Moon is Earth's natural satellite, while Earth moves around the Sun. Their positions and movements produce many familiar phenomena such as day and night, phases of the Moon, eclipses and changes in the apparent position of the Sun.
🌌 1. Celestial Objects
Objects that exist naturally in space are called celestial objects or celestial bodies.
Star
A star is a huge, hot celestial object that produces its own light and energy.
Planet
A planet is a celestial body that moves around a star in an orbit.
Natural Satellite
A natural satellite is a celestial body that revolves around a planet. The Moon is Earth's natural satellite.
Other Objects
Space also contains asteroids, comets, meteoroids and many other objects.
☀️ 2. The Sun
The Sun is the star at the centre of our Solar System. It is much larger than Earth and is extremely hot.
The Sun provides light and heat that are essential for life and for many processes occurring on Earth.
Why is the Sun important?
- It provides light to Earth.
- It provides heat and energy.
- Solar energy drives many processes on Earth.
- Plants use sunlight during photosynthesis.
- The Sun is the main source of energy for Earth's climate system.
🌍 3. The Earth
Earth is the third planet from the Sun and the only known planet to support life.
Earth has liquid water, a suitable atmosphere and conditions that allow a huge variety of living organisms to survive.
Water
Earth has abundant water, including oceans, rivers, lakes, glaciers and groundwater.
Atmosphere
Earth's atmosphere contains gases needed by living organisms and protects the planet in several ways.
Life
Earth supports an enormous diversity of plants, animals and microorganisms.
🔄 4. Rotation of the Earth
The Earth rotates around an imaginary line passing through its North and South Poles. This imaginary line is called the axis of rotation.
Earth takes approximately 24 hours to complete one rotation relative to the Sun, giving us the familiar cycle of day and night.
🌅 5. Day and Night
At any particular time, one half of Earth is illuminated by the Sun while the other half faces away from the Sun.
Day
The side of Earth facing the Sun experiences daylight.
Night
The side facing away from the Sun experiences night.
🔄 6. Revolution of the Earth
The Earth moves around the Sun along an approximately elliptical path called its orbit.
The movement of Earth around the Sun is called revolution.
Rotation → Earth spins on its axis.
Revolution → Earth moves around the Sun.
🌙 7. The Moon
The Moon is Earth's natural satellite. It does not produce its own visible light. The bright appearance of the Moon is caused by sunlight reflected from its surface.
Natural Satellite
The Moon revolves around Earth.
Reflected Sunlight
Moonlight that we see is sunlight reflected from the Moon.
Orbit
The Moon follows an orbit around Earth.
🔄 8. Movement of the Moon
The Moon rotates on its axis and also revolves around Earth. The time taken by the Moon to rotate once is approximately the same as the time it takes to complete one revolution around Earth.
🌒 9. Phases of the Moon
The Moon appears to change shape over the course of a month. These changing appearances are called the phases of the Moon.
The phases occur because we see different portions of the Moon's sunlit half as the Moon moves around Earth.
New Moon
The Moon is positioned approximately between Earth and the Sun, and its illuminated side faces away from Earth.
First Quarter
About half of the visible lunar disk appears illuminated.
Full Moon
The side of the Moon facing Earth appears almost completely illuminated.
Last Quarter
Again, approximately half of the visible lunar disk appears illuminated, but the opposite half is bright compared with the first quarter.
🌙 10. Moon Phase Cycle
🌑 11. What is an Eclipse?
An eclipse occurs when one celestial object moves into the shadow of another or blocks light from reaching another object.
The positions of the Sun, Earth and Moon are important in understanding eclipses.
☀️🌑 12. Solar Eclipse
A solar eclipse occurs when the Moon comes between the Sun and Earth and blocks some or all of the Sun's light from reaching a region of Earth.
🌍🌑 13. Lunar Eclipse
A lunar eclipse occurs when Earth comes between the Sun and Moon and Earth's shadow falls on the Moon.
🔍 14. Solar Eclipse vs Lunar Eclipse
| Solar Eclipse | Lunar Eclipse |
|---|---|
| Moon comes between Sun and Earth. | Earth comes between Sun and Moon. |
| Moon's shadow falls on part of Earth. | Earth's shadow falls on the Moon. |
| Occurs around new moon. | Occurs around full moon. |
| Visible from a relatively limited region of Earth. | Can be seen from a much larger portion of the night side of Earth. |
🌦️ 15. Seasons
Different parts of Earth experience different seasons during the year.
Seasons are mainly caused by Earth's tilted axis and its revolution around the Sun. Because Earth's axis remains pointed in nearly the same direction as Earth moves around the Sun, different hemispheres receive sunlight at different angles during different parts of the year.
Summer
A hemisphere experiences summer when it is tilted toward the Sun and receives more direct sunlight for longer periods.
Winter
A hemisphere experiences winter when it is tilted away from the Sun and receives less direct sunlight.
Spring
A transition season occurring between winter and summer in many regions.
Autumn
A transition season occurring between summer and winter in many regions.
🌍 16. Northern and Southern Hemispheres
Earth can be divided into the Northern Hemisphere and Southern Hemisphere by the equator.
| Northern Hemisphere | Southern Hemisphere |
|---|---|
| When the Northern Hemisphere is tilted toward the Sun, it experiences summer. | At the same time, the Southern Hemisphere experiences winter. |
| Its seasons are opposite to those in the Southern Hemisphere. | Its seasons are opposite to those in the Northern Hemisphere. |
🌊 17. The Moon and Tides
The Moon's gravity has an important effect on Earth's oceans. Along with the gravitational influence of the Sun, it contributes to the rise and fall of ocean water known as tides.
High Tide
A period when the water level of the sea rises to a relatively high level.
Low Tide
A period when the water level falls to a relatively low level.
🔗 18. Relationship Between Earth, Moon and Sun
The Earth, Moon and Sun interact as part of the Solar System. Their relative positions and movements help explain many phenomena observed from Earth.
- Earth's rotation causes the day-night cycle.
- Earth's revolution and axial tilt are important for seasons.
- The Moon's revolution around Earth produces changing phases.
- Particular alignments produce solar and lunar eclipses.
- The Moon's gravity contributes to ocean tides.
🔭 19. Observing the Sky
The sky appears to change continuously as Earth rotates and as the Moon moves along its orbit.
By observing the Moon regularly, students can notice that its shape changes in a predictable cycle. Similarly, the apparent movement of the Sun across the sky is connected to Earth's rotation.
⚡ Chapter 12 Quick Revision
- The Sun is a star at the centre of the Solar System.
- Earth is the third planet from the Sun and supports life.
- The Moon is Earth's natural satellite.
- Earth rotates on its axis, producing the cycle of day and night.
- Earth revolves around the Sun.
- The Moon rotates and revolves around Earth.
- The Moon appears bright because it reflects sunlight.
- The changing appearance of the Moon is called its phases.
- A solar eclipse occurs when the Moon comes between the Sun and Earth.
- A lunar eclipse occurs when Earth comes between the Sun and Moon.
- Earth's tilted axis and its revolution around the Sun are important causes of seasons.
- The Moon's gravity contributes to ocean tides.
- The Earth, Moon and Sun form a connected system whose movements produce many observable phenomena.
📖 Important Terms
✏️ Important Practice Questions
1. What is a celestial object?
A naturally occurring object in space, such as a star, planet or natural satellite, is called a celestial object.
2. Why is the Sun important for Earth?
The Sun provides light and heat and supplies energy that supports many processes on Earth, including photosynthesis.
3. What causes day and night?
Earth's rotation on its axis causes the regular alternation of day and night.
4. What is the difference between rotation and revolution?
Rotation is the spinning of an object around its own axis, while revolution is the movement of an object around another celestial body.
5. Why does the Moon appear to shine?
The Moon does not produce its own visible light. It appears bright because it reflects sunlight.
6. What are the phases of the Moon?
The changing appearances of the Moon as seen from Earth are called the phases of the Moon.
7. What causes the phases of the Moon?
As the Moon revolves around Earth, we see different portions of its sunlit half from Earth.
8. What is a solar eclipse?
A solar eclipse occurs when the Moon comes between the Sun and Earth and blocks some sunlight from reaching Earth.
9. What is a lunar eclipse?
A lunar eclipse occurs when Earth comes between the Sun and Moon and Earth's shadow falls on the Moon.
10. Why do seasons occur?
Seasons are mainly caused by Earth's axial tilt combined with Earth's revolution around the Sun.
11. What causes tides?
The gravitational influence of the Moon, together with that of the Sun, contributes to the rise and fall of ocean water called tides.
🤔 Think & Explore
❓ Frequently Asked Questions
What is Chapter 12 of Class 7 Science?
Chapter 12 of Class 7 Science is titled Earth, Moon, and the Sun.
What are the main topics in this chapter?
The chapter discusses the Earth, Moon and Sun, Earth's rotation and revolution, phases of the Moon, eclipses, seasons and the relationship between these celestial bodies.
Is the Moon a star?
No. The Moon is Earth's natural satellite. It does not produce its own visible light.
Why does the Moon shine?
The Moon appears to shine because it reflects sunlight.
What causes day and night?
Earth's rotation on its axis causes day and night.
What is the difference between a solar and lunar eclipse?
During a solar eclipse, the Moon comes between the Sun and Earth. During a lunar eclipse, Earth comes between the Sun and Moon.
Why do seasons change?
Seasons are mainly caused by Earth's tilted axis and its revolution around the Sun.
What causes ocean tides?
The gravitational effects of the Moon and Sun contribute to the rise and fall of ocean water called tides.