Students can rely on these Class 7 Curiosity Notes and Class 7 Science Curiosity Chapter 12 Earth Moon and the Sun Notes for complete exam preparation.
Class 7 Science Chapter 12 Earth Moon and the Sun Notes
Class 7 Science Curiosity Chapter 12 Notes
Earth Moon and the Sun Notes Class 7
→ Rotation: The spinning motion of an object, like the Earth, around its own axis, completing one turn in about 24 hours.
→ Axis of Rotation: An imaginary line passing through the North and South Poles, around which the Earth rotates.
→ Revolution: The motion of an object, like the earth around another object, such as the Sun, taking about 365 days and 6 hours.
→ Orbit: The nearly circular path the Earth follows while revolving around the Sun.
→ Solstica: The longest (summer solstice, around June 21) or shortest (winter solstice, around December 22) day in the Nothern Hemisphere, due to the Earth’s tilt.
→ Equinox: Days when day and night are equal (12 hours each), occurring around March 21 (spring equinox) and September 23 (autumn equinox) in the Northern Hemisphere.
→ Solar Eclipse: An event where the Moon blocks sunlight from reaching Earth, casting a shadow that makes the Moon appear dark red (total) or partially shadowed (partial).
→ Apparent Size: The perceived size of an object in the sky, depending on its actual size and distance from the observer, allowing the Moon to appear as large as the Sun during a solar eclipse.
→ Transit of Venus: A rare event where Venus appears as a small black dot crossing the Sun’s face, due to its small apparent size compared to the Sun.
→ Earth’s rotation causes day/night and apparent motion of celestial bodies.
→ Earth’s revolution and tilted axis cause changing night sky and seasons.
→ The Earth’s axis of rotation is not upright with respect to the orbit, but is tilted.
→ Seasons occur because of the tilt of the Earth’s axis of rotation and its spherical shape.
→ A solar eclipse occurs when the Moon is in the path of the Sun as seen from the Earth, and sunlight is blocked from reaching the Earth.
→ A lunar eclipse occurs when the Earth comes in between the Sun and the Moon, blocking sunlight from reaching the Moon.
→ The Earth rotates on its own axis in about 24 hours.
→ The Earth’s rotation from West to East causes day and night as well as the apparent motion of the Sun, the Moon, and the stars.
→ The Earth revolves around the Sun and takes nearly 1 year to complete a revolution.
Class 7 Earth Moon and the Sun Notes
Introduction:
The earth, moon and sun forms the essential system that governs our experience of time, light and cycles on our planet. While cycling to school in morning one day Rashmika notices that coconut tree shadows were long, but in afternoon while coming back she notices that coconut trees shadows are shorter. Being curious she was puzzled and so many questions generates in her mind. Have you ever looked up at the night sky and wondered what lies beyond the clouds? The dark sky is filled with shining dots – some twinkle, some glow steadily.
These are stars, planets, and our closest neighbour, the Moon. In this chapter, we’ll explore the fascinating world of celestial bodies – objects that exist in space. You will learn about the Earth, our unique planet that supports life, the Moon, which goes through different phases every month, and stars, which are glowing balls of gases far away in space.
Rotation of the Earth:
Rotation is the spinning of an object around its own axis. The earth’s rotation from west to east causes the day-night cycle and due to the rotation of the earth, the sun appears to rise in the eastward direction, move across the sky from the east to the west and set in the westward direction.
Sun rises in the east and sets in the west. Let’s understand this through an activity:
Precautions:
1. Move around carefully and take help of your elders while performing.
In which way is the Earth turning around itself?
To visualise that earth is turning around itself, lets collect some of the objects that turn around themselves.
Rotation is the motion of an object in which all its parts move in circles around an imaginary line that passes through it. This line is called the axis of rotation.
Similarly, the earth rotates (spins) on its axis. The Earth’s axis of rotation passes through its geographic North Pole and the South Pole. The Earth completes one rotation in about 24 hours. You can also view from Top of the north pole, the Earth is rotating in the anti-clockwise direction, that is, from West to East. Let’s understand this by performing activity.
Day and Night Cycle:
The earth’s rotation causes one side to face the sun, experiencing the day time and opposite side faces away from the sun, experiencing night time or darkness. Let us now further explore to understand how day and night occur on the earth due to its rotation. Go to a dark room, shine light from the torch placed at some distance (1.5 m) on the globe as shown in Fig.4(b). Now, note down your observation.
- Half of the globe receives the light from the torch, while the other half stays dark.
- In day time in that half of the globe which receives light, and night time in the other half.
- In India, sunrise first occurs in the eastern part and then in other parts.
- The light falls on the eastern part of India first when the globe rotates from West to East with respect to the North-South axis of the globe.
- Sunrise occurs as your location moves into light and sunset occurs as it moves into darkness.
Apparent Motion of Celestial Objects:
The Earth’s rotation from West to East causes the day-night cycle. As shown in Fig.5, the side facing the Sun experiences daytime, while the other side is dark and experiences night.
Stand on the Equator on the Earth, watch the sky during one rotation of the Earth while it rotates from West to East. Due to this rotation sun seems to rise in eastward direction only, move across the sky from the East to the West and set in the westward direction, the night begins and the stars become visible in the sky.
Fascinating Facts:
Foucault Pendulum demonstrates earth’s rotation physically using a swinging pendulum that changes its plane of oscillation over time.
Fascinating Facts:
In a photograph, the apparent motion of the stars is recorded as arcs of a circle, known as star trails. Astrophotographers (taking long exposure).
Aryabhata, a famous mathematician, also noticed the daily apparent motion of the celestial objects. He explained it in verse 9, Golapada, Aryabhatiya that time taken by the earth to complete one full rotation about its axis is around 23 hrs 56 minutes. (4.1 seconds in modern minutes). This value is close to the currently accepted value.
The Bhil and Pawara are indigenous communities from the Tapi Valley in western India, who used the appearance of certain patterns of stars in the sky as markers for the arrival of monsoon rain.
Revolution of the Earth:
This movement is different from Rotation. Revolution is defined ‘as a motion of object around another object”. The path of any object takes when it revolves around other object is called orbit. Example orbit of sun earth is almost circular in shape. Moreover an orbit seems to be elongated (side view of an orbit). In app. 365 days, 6 hours time, earth completes one revolution around sun.
Changing view of night sky from the Earth:
It is well known to us that,”The sun sets in west.” Night sky is visible after sun sets. “Its reason is rotation of earth.” Earth is revolving around sun in a constant rate. Stars are visible at night, therefore sky changes after sun sets slowly over a year as when you observe in varied directions too. As seen in Fig.8.- the change occurs when we see patterns of stars at fix time of night, on days separated by a month.
Seasons on the Earth:
The Earth’s axis is tilted at an angle relative to its orbit around sun. This tilt, along with the Earth’s spherical shape causes the different seasons we experience. Around June 21, the Northern Hemisphere tilts towards the Sun, receiving more direct and intense sunlight. During this time, the Sun stays above the horizon for more than 12 hours, resulting summer in the Northern Hemisphere. At the same time, the Southern Hemisphere tilts away from the Sun, getting less direct sunlight and shorter daylight hours, causing winter there.
Around December 22, the situation reverses; the Northern Hemisphere tilts away from the Sun, leading to winter, while the Southern Hemisphere tilts towards the Sun, enjoying summer. The difference in the Sun’s intensity and the length of the day during these times causes the changes in temperature and weather that define the seasons.
The seasons and the length of daytime are reversed in the Southern Hemisphere as compared to the Northern Hemisphere. There it is winter in June, and summer in December, as shown in Fig. 10 and Fig 11.
The polar regions experience extreme daylight conditions – either six months of continuous daylight (known as the Midnight Sun) or six months of darkness. At the North Pole, the Sun rises on March 21 and stays above the horizon for six months, setting on September 22. The South Pole experiences the opposite-six months of darkness followed by six months of daylight.
In the Northern Hemisphere, the longest day of the year, called the summer solstica, occurs around June 21. The shortest day, known as the winter solstica, happens around December 22. On March 21 (the spiring equinox) and September 23 (the autumn equinox), day and night are equal, each lasting about 12 hours.
Misconception about seasons:
1. Seasons are not caused by the earth being closer to the sun when tilted toward it or by an oval orbit with significant distance variations.
2. The earth is actually closest to the sun in January, but the tilt and spherical shape are the primary reasons for seasonal changes.
Eclipses:
Eclipses occur when one celestial body blocks light from another, casting a shadow. The Moon’s position relative to the Earth and Sun causes solar and lunar eclipses – Two main types of eclipses:
Solar Eclipse:
A solar eclipse occurs when the Moon comes between the Earth and the Sun, blocking sunlight from reaching certain part of the earth. Although the Moon is much smaller than the Sun, their apparent sizes in the sky are similar because the Moon is much closer to Earth. This alignment allows the Moon to fully or partially cover the Sun. The shadow of the Moon falls on a small area on the surface of the Earth as seen in Fig. 12 This area is in total darkness, and no part of the Sun can be seen from there. The observers in this area witness a total solar eclipse. Arrangement of sun, moon and earth during a solar eclipse.
Types of Solar Eclipses:
Safe Viewing of Solar Eclipses:
Direct viewing of a solar eclipse is dangerous because the Sun’s intense light can cause permanent blindness, even when the Sun is only partially covered by the Moon.
Safe methods for viewing a solar eclipse include:
- Using specialised solar goggles designed for eclipse viewing.
- Attending organised viewing events where safety measures are in place.
- Projecting the Sun’s image using a mirror to watch the eclipse safely.
Superstitions about eclipses, like avoiding eating or going outside, stemmed from historical fears but are no longer necessary with our modern understanding of eclipses.
The Sanskrit word for eclipse is “grahan”. These texts use poetic shlokas to describe the phenomenon.
Lunar Eclipse:
A lunar eclipse occurs when the Earth comes between the Sun and the Moon, blocking the sunlight from reaching the Moon. This results in the Earth’s shadow falling on the Moon. The event is only visible during a full moon, when the Earth is directly aligned between the Sun and the Moon.
Types of Lunar Eclipses:
1. Total Lunar Eclipse: In a total lunar eclipse, the Moon is completely covered by the Earth’s shadow. During this event, the Moon takes on a dark red colour, which is often referred to as a “blood moon”. The reddish hue is caused by the Earth’s atmosphere scattering sunlight, which then reaches the Moon. The Moon remains red until it moves out of the Earth’s shadow.
2. Partial Lunar Eclipse: In a partial lunar eclipse, only part of the Moon enters the Earth’s shadow. The rest of the Moon remains visible and appears unaffected. This creates a distinctive shape where part of the Moon looks darker and the rest remains bright.
Viewing a Lunar Eclipse:
1. Unlike a solar eclipse, a lunar eclipse is safe to watch with the naked eye. Since the moon is not as bright as the sun, the earth’s shadow provides a dimmer, more diffuse light.
2. It is also possible to observe both total and partial lunar eclipses from the earth without special protection, making them easier for amateur astronomers and unthusiasts to view.
The KodaikanalSolar Observatory is located in the beautiful Palani range of hills in southern India. It was established in 1899 and has provided data about the Sun for over 100 years. It is operated by the Indian Institute of Astrophysics (IIA), Bengaluru.
