Class 7 Science NCERT Notes – Chapter 12: Earth, Moon, and the Sun (PDF, MindMap, Q&A, Quizzes)

Chapter 12 (Science): Earth, Moon, and the Sun – CBSE Class 7 NCERT Science Detailed Study Notes.

1. The Earth’s Motion and Its Effects

1.1 Earth’s Rotation

The Earth spins, or rotates, on its own axis in space. This motion is similar to a spinning top, fan, or ball.

• Axis of Rotation: An imaginary line that passes through the geographic North Pole and South Pole, around which the Earth spins.
• Direction of Rotation: When viewed from above the North Pole, the Earth rotates in an anti-clockwise direction, which is from West to East.
• Duration of Rotation: The Earth completes one full rotation in approximately 24 hours. Ancient Indian astronomer Aryabhata calculated this value to be around 23 hours, 56 minutes, and 4.1 seconds, which is impressively close to the modern accepted value.

1.2 Effects of Earth’s Rotation

• Day and Night Cycle: The Earth’s rotation is the primary cause of the day-night cycle. The side of the Earth facing the Sun experiences daytime, while the opposite side, which is in darkness, experiences nighttime. As the Earth rotates from West to East, a location moves from darkness into sunlight (sunrise) and later from sunlight into darkness (sunset).
• Apparent Motion of Celestial Bodies: Because we view celestial objects from a rotating Earth, they appear to move across the sky.
  • The Sun: Appears to rise in the East, move across the sky, and set in the West. This is an apparent motion caused by the Earth’s West-to-East rotation. The changing length of shadows throughout the day (long in the morning, shorter in the afternoon) is a direct consequence of this apparent motion.
  • The Moon and Stars: Similar to the Sun, the Moon and stars also appear to rise in the eastward direction and set in the westward direction due to the Earth’s rotation.
• Apparent Motion of Stars around the Pole Star: The Earth’s axis of rotation in the Northern Hemisphere points very close to the Pole Star (Dhruva Tara). Consequently, the Pole Star appears nearly stationary, while all other stars in the night sky appear to move in circles around it. This effect can be captured in long-exposure photographs as “star trails.”

2. The Earth’s Revolution and the Seasons

2.1 Earth’s Revolution

The Earth revolves around the Sun in an oval-shaped path called an orbit. It takes nearly one year to complete a single revolution.

2.2 The Cause of Seasons

Seasons are caused by the combination of the tilt of the Earth’s axis of rotation and its revolution around the Sun. The Earth’s axis is not upright relative to its orbit but is tilted.

• The Tilt: This tilt means that for part of the year, the Northern Hemisphere is tilted towards the Sun, and for another part, it is tilted away. The same applies to the Southern Hemisphere, but in an opposite cycle.
• Intensity of Sunlight: Due to the Earth’s spherical shape, when a hemisphere is tilted towards the Sun, sunlight is concentrated over a smaller area, making it more intense and leading to warmer temperatures. When tilted away, the same amount of sunlight spreads over a larger area, becoming less intense and causing cooler temperatures.
• Duration of Daylight: The tilt also affects the length of the day. The hemisphere tilted towards the Sun experiences more than 12 hours of daylight.

2.3 Seasons in the Hemispheres

• Summer in the Northern Hemisphere (around June):
  • The Northern Hemisphere is tilted towards the Sun.
  • Sunlight is more intense (concentrated on a smaller area).
  • Daytime lasts longer than 12 hours.
  • The North Pole receives sunlight for all 24 hours.
  • The Southern Hemisphere experiences winter during this time.
• Winter in the Northern Hemisphere (around December):
  • The Northern Hemisphere is tilted away from the Sun.
  • Sunlight is less intense (spread over a larger area).
  • Daytime is shorter, and nighttime is longer than 12 hours.
  • The North Pole is in darkness for all 24 hours.
  • The Southern Hemisphere experiences summer during this time.
• Equatorial Regions: For regions near the equator, like the southern states of India, the effect of seasons is not very prominent because there is little difference in the intensity of sunrays and the length of the day (always around 12 hours of sunlight) throughout the year.

3. Eclipses

An eclipse occurs when one celestial body blocks the light from another.

3.1 Solar Eclipses

A solar eclipse happens when the Moon passes directly between the Sun and the Earth, blocking the Sun’s light from reaching a part of the Earth. The Moon’s shadow falls on the Earth.

• Apparent Size: The Moon, despite being much smaller than the Sun, can completely block it because it is much closer to Earth. This makes their apparent sizes in the sky nearly identical. Planets like Mercury and Venus are much larger than the Moon but are also much farther away, so their apparent sizes are too small to cause a total eclipse; their passage in front of the Sun is called a “transit.”
• Types of Solar Eclipses:
  • Total Solar Eclipse: Occurs in the small area on Earth where the Moon’s shadow causes total darkness. The entire Sun is blocked from view.
  • Partial Solar Eclipse: Seen from a larger surrounding area where only a part of the Sun is blocked by the Moon.
• Safety Warning: It is extremely dangerous to look directly at the Sun during a solar eclipse without specialized eye protection. Safe viewing methods include using solar eclipse goggles or projecting the Sun’s image onto a screen using a mirror or binoculars. Participating in events organized by planetaria or astronomy clubs is recommended.

3.2 Lunar Eclipses

A lunar eclipse occurs when the Earth passes directly between the Sun and the Moon. The Earth blocks sunlight from reaching the Moon, casting its shadow on the full lunar disc.

4. Historical and Cultural Perspectives

• Aryabhata: A renowned mathematician and astronomer of ancient India (around the fifth century CE). In his treatise Aryabhatiya, he correctly explained that the apparent westward motion of the stars is due to the Earth’s rotation, using the analogy of a person in a moving boat seeing stationary objects on the shore as moving backward.
• Surya Siddhanta: An ancient Indian astronomical text written in Sanskrit shlokas that provides calculations to predict eclipses.
• Bhil and Pawara Communities: Indigenous communities from the Tapi Valley in western India who traditionally used the appearance of certain star patterns as markers for the arrival of the monsoon.
• Foucault Pendulum: A 22-meter-long Foucault pendulum is installed in the Constitution Hall of the new Parliament building in New Delhi, symbolizing the integration of the idea of India with the cosmos.
• Modern Indian Astronomy:
  • M.K. Vainu Bappu: Known as the father of modern Indian astronomy. He led the establishment of major telescopes, including those at Manora Peak (Nainital) and Kavalur (Tamil Nadu). The Kavalur observatory is named after him.
  • Kodaikanal Solar Observatory: Established in 1899 in the Palani hills of southern India, it has provided over 100 years of solar data and is operated by the Indian Institute of Astrophysics (IIA), Bengaluru.

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Quiz and Q&A Section

Short-Answer Quiz (2-3 sentences each)

1. What is the primary cause of the day-night cycle on Earth?
2. In which direction does the Earth rotate, and what is the observable effect of this rotation on the Sun’s position?
3. Define the Earth’s axis of rotation.
4. Why does the Pole Star (Dhruva Tara) appear almost stationary in the night sky?
5. What two factors are responsible for the occurrence of seasons on Earth?
6. Explain why summer in the Northern Hemisphere is warmer, considering both the intensity and duration of sunlight.
7. Describe the conditions in the Southern Hemisphere when it is winter in the Northern Hemisphere.
8. What is a solar eclipse?
9. Why can the Moon, which is much smaller than the Sun, cause a total solar eclipse?
10. What is the difference between a total solar eclipse and a partial solar eclipse?
11. What is a lunar eclipse?
12. Why is it dangerous to view a solar eclipse with the naked eye?
13. Describe one safe method for observing a solar eclipse.
14. Who was Aryabhata, and what was his significant contribution to understanding Earth’s motion?
15. How did the Bhil and Pawara communities use their knowledge of the stars?
16. How long does it take for the Earth to complete one rotation, according to both modern science and Aryabhata’s calculation?
17. Why do regions near the equator not experience prominent seasonal changes?
18. What is a “Transit of Venus,” and why is it not considered a solar eclipse?
19. What is a “star trail” in astrophotography?
20. Who is considered the father of modern Indian astronomy, and what is one of his major achievements?
21. What observation did Rashmika make about coconut tree shadows that sparked her curiosity?
22. Using the merry-go-round analogy, explain why the Sun appears to move from East to West.
23. Where is the Kodaikanal Solar Observatory located, and what is its significance?
24. What does the Foucault pendulum in the new Parliament building in New Delhi symbolize?
25. How does the apparent motion of the Big Dipper (Saptarishi) constellation throughout the night provide evidence of Earth’s rotation?

Multiple-Choice Quiz

1. When viewed from above the North Pole, the Earth rotates in which direction? a) Clockwise (East to West) b) Anti-clockwise (West to East) c) North to South d) It does not rotate.
2. The Earth completes one rotation in approximately: a) 365 days b) 12 hours c) 24 hours d) 29.5 days
3. What is the main reason for the changing seasons on Earth? a) The Earth’s changing distance from the Sun. b) The tilt of the Earth’s axis of rotation. c) The Earth’s rotation on its axis. d) The blocking of sunlight by the Moon.
4. During which month is the Northern Hemisphere tilted towards the Sun, experiencing summer? a) December b) March c) September d) June
5. A solar eclipse occurs when: a) The Earth is between the Sun and the Moon. b) The Sun is between the Earth and the Moon. c) The Moon is between the Sun and the Earth. d) The Earth’s shadow falls on the Moon.
6. The term for the size of an object as seen by an observer, which depends on both its actual size and distance, is: a) Physical size b) Apparent size c) Relative size d) Ecliptic size
7. Who explained the apparent motion of stars using the analogy of a man in a moving boat? a) M.K. Vainu Bappu b) Rashmika c) Aryabhata d) The Surya Siddhanta
8. The Kavalur observatory in Tamil Nadu is named after which astronomer? a) Aryabhata b) Vainu Bappu c) The Bhil community leaders d) The Kodaikanal founders
9. At the North Pole, how long does the period of continuous sunshine last? a) 24 hours b) One month c) Three months d) Six months
10. Which of the following is an unsafe way to view a solar eclipse? a) Using solar eclipse goggles. b) Looking directly at the Sun. c) Projecting the Sun’s image with a mirror. d) Attending a program at a planetarium.
11. A lunar eclipse happens when the ______ is between the ______ and the ______. a) Moon; Sun; Earth b) Sun; Earth; Moon c) Earth; Sun; Moon d) None of the above
12. The indigenous communities who used star patterns to predict monsoons were the: a) Kavalur and Kodaikanal b) Bhil and Pawara c) Saptarishi and Dhruva d) Aryabhatiya and Siddhanta
13. What is the length of the Foucault pendulum in the new Indian Parliament building? a) 12 metres b) 22 metres c) 50 metres d) 100 metres
14. The ancient Indian text providing calculations to predict eclipses is the: a) Aryabhatiya b) Curiosity c) Exploring Society d) Surya Siddhanta
15. Why don’t Mercury and Venus cause total solar eclipses? a) They are smaller than the Moon. b) They are too far away, making their apparent size too small. c) They do not pass between the Earth and Sun. d) They do not have shadows.
16. On the equator, the length of daytime is consistently: a) 10 hours b) 12 hours c) 14 hours d) It varies significantly.
17. The apparent circular motion of stars recorded in long-exposure photos are called: a) Solar flares b) Star trails c) Lunar arcs d) Pole orbits
18. What happens to the intensity of sunrays when they are spread over a larger area? a) They become more intense. b) They become less intense. c) The intensity does not change. d) They disappear completely.
19. In December, the North Pole is in darkness for: a) 6 hours b) 12 hours c) 24 hours d) 6 months
20. A ‘Transit’ is when a planet like Venus appears as a tiny black dot against the Sun’s face. This event is: a) Very common b) A type of lunar eclipse c) A rare event d) A cause of seasons

Essay Questions

1. Explain in detail how the Earth’s rotation on its tilted axis and its revolution around the Sun work together to create the seasons. Describe the specific conditions for summer and winter in the Northern Hemisphere.
   • Answer: The seasons are not caused by the Earth’s distance from the Sun but by the tilt of its axis of rotation, which is not upright with respect to its orbital path. As the Earth revolves around the Sun over the course of a year, this tilt causes different parts of the Earth to receive more direct sunlight than others. During the summer in the Northern Hemisphere (around June), this hemisphere is tilted towards the Sun. This tilt has two main effects: first, the sun’s rays are more concentrated, falling on a smaller area, which makes the sunlight more intense and leads to more heating. Second, the days are longer, with more than 12 hours of sunlight, allowing more time for the surface to heat up. Conversely, during winter in the Northern Hemisphere (around December), it is tilted away from the Sun. The sun’s rays are spread over a larger area, making them less intense, and the days are shorter, with less than 12 hours of daylight, leading to cooler temperatures. The revolution of the Earth ensures this cycle repeats annually.
2. Compare and contrast solar and lunar eclipses. Discuss the alignment of the Sun, Earth, and Moon for each, and explain why one is visible from a much larger area of Earth than the other.
   • Answer: A solar eclipse and a lunar eclipse are both astronomical events caused by the alignment of the Sun, Earth, and Moon, but they differ in their configuration and visibility. A solar eclipse occurs when the Moon is positioned directly between the Sun and the Earth, causing the Moon’s shadow to fall on a small portion of the Earth. A lunar eclipse occurs when the Earth is positioned directly between the Sun and the Moon, causing the Earth’s shadow to fall on the Moon.
   • The reason for the difference in visibility lies in the size of the shadow. During a solar eclipse, the Moon casts a relatively small shadow on the Earth, so only observers within that small path can see a total eclipse. During a lunar eclipse, the Earth casts a much larger shadow on the Moon. Therefore, a lunar eclipse can be seen by anyone on the night side of the Earth where the Moon is visible in the sky.
3. Discuss the concept of ‘apparent size’ and explain how it allows the Moon to cause a total solar eclipse, while larger planets like Venus cannot.
   • Answer: ‘Apparent size’ refers to how large an object appears to an observer, which is determined by both its actual physical size and its distance from the observer. An object that is very large but far away can appear smaller than a small object that is very close. This principle explains why the Moon can cause a total solar eclipse. Although the Sun’s physical diameter is about 400 times larger than the Moon’s, the Sun is also about 400 times farther away from Earth than the Moon is. This coincidence makes their apparent sizes in the sky almost identical. Therefore, when the Moon passes directly in front of the Sun, it can appear to cover the entire solar disk. In contrast, planets like Venus, while physically much larger than the Moon, are also significantly farther from Earth. This great distance makes their apparent size in our sky much smaller than the Sun’s, so when they pass between the Earth and the Sun during a ‘transit’, they only appear as a tiny dot and cannot block the Sun’s light.
4. Describe the evidence for Earth’s rotation that can be observed from Earth without specialized equipment. Use the examples of the Sun’s daily path, shadow lengths, and the movement of constellations.
   • Answer: Several observations provide daily evidence of the Earth’s rotation. The most obvious is the apparent motion of the Sun, which seems to rise in the East, travel across the sky, and set in the West. This is not the Sun moving, but rather the Earth rotating from West to East. A direct consequence is the change in shadow lengths; for example, a tree’s shadow is long in the morning, becomes shortest around midday, and lengthens again in the afternoon. At night, a similar effect is seen with the stars. Constellations like the Big Dipper (Saptarishi) appear to move across the sky, seemingly rotating around the nearly fixed Pole Star over several hours. This collective apparent movement of all celestial bodies is a direct result of our perspective from the spinning Earth.
5. Summarize the contributions of ancient Indian astronomy as presented in the text, focusing on Aryabhata and the Surya Siddhanta.
   • Answer: The provided text highlights significant contributions from ancient Indian astronomy. Aryabhata, a prominent astronomer from the fifth century CE, made a groundbreaking argument in his work, Aryabhatiya. He correctly deduced that the Earth rotates on its axis, causing the apparent westward movement of stationary stars. He illustrated this with the powerful analogy of a person on a moving boat perceiving stationary objects on the bank as moving backward. Furthermore, his calculation for the duration of Earth’s rotation (23 hours 56 minutes 4.1 seconds) is remarkably accurate. Another key text mentioned is the Surya Siddhanta, a classic Sanskrit text known for providing detailed methods and calculations for predicting the occurrences of both solar and lunar eclipses, demonstrating an advanced understanding of celestial mechanics.
6. Explain the phenomenon of ‘star trails’ and their relationship to the Pole Star.
   • Answer: ‘Star trails’ are arcs of light created by stars in a long-exposure photograph of the night sky. Astrophotographers achieve this by keeping the camera’s shutter open for an extended period, which captures the apparent motion of the stars as they seem to move across the sky. This apparent motion is not due to the stars themselves moving, but is a direct result of the Earth’s rotation on its axis. In the Northern Hemisphere, the Earth’s axis of rotation points very close to the Pole Star (Dhruva Tara), making it appear stationary. Because of this, the star trails in the photograph form concentric circles or arcs centered around the point in the sky where the Pole Star is located.
7. Why do the polar regions experience six months of continuous daylight followed by six months of darkness?
   • Answer: This unique phenomenon is a direct result of the Earth’s axial tilt of approximately 23.5 degrees. As the Earth revolves around the Sun, this tilt causes one pole to be pointed towards the Sun for an extended period while the other is pointed away. For instance, around June, the Northern Hemisphere is tilted towards the Sun, causing the North Pole and the surrounding arctic region to be continuously illuminated by sunlight for about six months, even as the Earth rotates. During this same period, the South Pole is tilted away from the Sun and experiences six months of darkness. The situation reverses six months later in December, when the Southern Hemisphere is tilted towards the Sun, giving the South Pole its six months of continuous daylight.
8. Describe the safe and unsafe ways to view a solar eclipse as detailed in the text.
   • Answer: The text strongly warns against unsafe viewing practices for a solar eclipse, chief among them being looking directly at the Sun with the naked eye. This can cause severe and permanent eye damage. The text outlines several safe methods. The safest approach is to use specialized eye protection, such as certified solar eclipse goggles. Another safe method is indirect viewing, where an image of the Sun is projected onto a surface; this can be done using a mirror, binoculars, or a telescope aimed away from the observer and towards a screen. The text also highly recommends participating in public viewing events organized by scientific institutions like planetaria or astronomy clubs, as they provide both the correct safety equipment and scientific explanations.
9. Who was M.K. Vainu Bappu and why is he a significant figure in Indian science?
   • Answer: M.K. Vainu Bappu is known as the father of modern Indian astronomy. His significance lies in his leadership and efforts to establish modern astronomical infrastructure in India. He was instrumental in setting up major instruments and telescopes, including those at Manora Peak near Nainital (Uttarakhand) and at Kavalur (Tamil Nadu). In recognition of his foundational work, the observatory at Kavalur was named the Vainu Bappu Observatory. His scientific work included the study of stars and the discovery of a comet, and he also traveled globally to study solar eclipses, contributing to India’s position in the international astronomical community.
10. Based on the text, what kind of astronomical and societal information can be gathered by observing the stars over time? Use the examples of the Big Dipper, the Bhil and Pawara communities, and changing constellations.
    • Answer: Observing the stars over time reveals crucial information about both Earth’s motion and societal practices. Observing the Big Dipper’s position relative to the Pole Star over a single night demonstrates the Earth’s daily rotation. Observing which constellations are visible in the eastern sky at sunset over different months reveals the Earth’s yearly revolution around the Sun, as our nighttime view of the cosmos changes. The text also shows how these observations have societal importance. For example, the Bhil and Pawara indigenous communities of western India historically used the appearance of specific star patterns as a reliable calendar to mark the arrival of the monsoon, which was critical for their agriculture and way of life.

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Answer Keys

Short-Answer Quiz – Answer Key

1. The day-night cycle is caused by the Earth’s rotation on its axis. As it spins, one half of the planet faces the Sun (day) while the other half is in shadow (night).
2. The Earth rotates from West to East (anti-clockwise when viewed from the North Pole). This rotation causes the Sun to have an apparent motion across the sky from East to West.
3. The Earth’s axis of rotation is an imaginary line passing through its geographic North and South Poles. The Earth spins around this line.
4. The Pole Star appears almost stationary because the Earth’s axis of rotation in the Northern Hemisphere points very closely towards it. As the Earth spins, the stars appear to circle this fixed point.
5. Seasons are caused by the combination of the Earth’s revolution around the Sun and the tilt of its axis of rotation.
6. Summer in the Northern Hemisphere is warmer because the hemisphere is tilted towards the Sun. This causes sunrays to be concentrated on a smaller area, making them more intense, and it also results in longer daylight hours (more than 12 hours).
7. When it is winter in the Northern Hemisphere (around December), the Southern Hemisphere is tilted towards the Sun. It experiences summer, with more intense sunlight and longer days.
8. A solar eclipse is an event that occurs when the Moon passes between the Sun and Earth. The Moon’s shadow is cast upon the Earth, blocking the Sun’s light from reaching that area.
9. The Moon can cause a total solar eclipse due to the concept of ‘apparent size’. Although the Moon is physically much smaller, it is also much closer to Earth than the Sun, which makes their apparent sizes in the sky almost identical.
10. A total solar eclipse is when the Moon completely blocks the Sun’s disk, visible from a small area on Earth. A partial solar eclipse occurs when the Moon only blocks a portion of the Sun, visible from a much larger area.
11. A lunar eclipse happens when the Earth comes between the Sun and the Moon. The Earth’s shadow falls on the Moon, blocking the sunlight that normally illuminates it.
12. It is dangerous because looking directly at the Sun, even when partially covered, can cause severe and permanent eye damage. The intense solar radiation can burn the retina.
13. One safe method is to project the Sun’s image onto a screen or wall using a mirror, binoculars, or a telescope. Another is to use certified solar eclipse goggles.
14. Aryabhata was an ancient Indian astronomer and mathematician. He correctly explained that the apparent westward motion of stars is caused by the Earth’s own rotation on its axis.
15. The Bhil and Pawara indigenous communities from the Tapi Valley used the appearance of certain patterns of stars in the sky as markers for the arrival of the monsoon.
16. Modern science states the Earth rotates in about 24 hours. Aryabhata’s calculation was remarkably close, at approximately 23 hours, 56 minutes, and 4.1 seconds.
17. Regions near the equator receive about 12 hours of sunlight year-round. There is also very little difference in the intensity of sunrays falling on the equator in different months, so the effects of seasons are not prominent.
18. A “Transit of Venus” is when Venus passes between the Sun and Earth. It is not an eclipse because Venus’s apparent size is too small to block the Sun; it just appears as a tiny black dot.
19. A ‘star trail’ is an arc of light seen in a long-exposure photograph of the night sky. It records the apparent motion of the stars, which is caused by the Earth’s rotation.
20. M.K. Vainu Bappu is considered the father of modern Indian astronomy. A major achievement was leading the establishment of many modern telescopes in India, such as the ones at Kavalur and Nainital.
21. Rashmika noticed that the shadows of coconut trees were long in the morning but shorter in the afternoon. This made her wonder about the movement of the Sun and the Earth.
22. When on a merry-go-round turning anti-clockwise, stationary objects outside appear to move in the opposite (clockwise) direction. Similarly, because the Earth rotates from West to East (anti-clockwise), the Sun appears to move from East to West.
23. The Kodaikanal Solar Observatory is located in the Palani range of hills in southern India. It is significant for providing over 100 years of continuous data about the Sun.
24. The Foucault pendulum symbolizes the integration of the idea of India with the vastness of the cosmos.
25. Over several hours on a single night, the Big Dipper appears to move in an arc around the nearly stationary Pole Star. This apparent motion is direct evidence that the Earth is rotating on its axis.

Multiple-Choice Quiz – Answer Key

1. b) Anti-clockwise (West to East)
2. c) 24 hours
3. b) The tilt of the Earth’s axis of rotation.
4. d) June
5. c) The Moon is between the Sun and the Earth.
6. b) Apparent size
7. c) Aryabhata
8. b) Vainu Bappu
9. d) Six months
10. b) Looking directly at the Sun.
11. c) Earth; Sun; Moon
12. b) Bhil and Pawara
13. b) 22 metres
14. d) Surya Siddhanta
15. b) They are too far away, making their apparent size too small.
16. b) 12 hours
17. b) Star trails
18. b) They become less intense.
19. c) 24 hours
20. c) A rare event

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Glossary of Key Terms

Term	Definition
Apparent Size	The size of an object as seen by the eye, which depends upon both its actual physical size and its distance from the observer.
Aryabhata	A famous mathematician and astronomer of ancient India (around the fifth century CE) who explained the apparent motion of stars as a result of Earth’s rotation.
Axis of Rotation	An imaginary line that passes through an object, around which all its parts move in circles. The Earth’s axis passes through the North and South Poles.
Big Dipper	A constellation, also known as Saptarishi in India.
Eclipse	An event where sunlight is blocked. Known as grahan in Sanskrit.
Lunar Eclipse	An event that occurs when the Earth blocks sunlight from reaching the Moon, casting a shadow on the full lunar disc.
M.K. Vainu Bappu	Known as the father of modern Indian astronomy, he led efforts in setting up many modern telescopes in India.
Pole Star	A star (Dhruva Tara) that appears nearly stationary in the sky because the Earth’s axis of rotation points very close to it.
Revolution	The motion of the Earth as it moves around the Sun in its orbit.
Rotation	The motion of an object in which all its parts move in circles around an imaginary line that passes through it. The Earth’s rotation on its axis causes day and night.
Solar Eclipse	An event that occurs when the Moon is in the path of the Sun as seen from the Earth, and sunlight is blocked from reaching the Earth.
Star Trails	Arcs of a circle recorded in a long-exposure photograph that show the apparent motion of the stars due to Earth’s rotation.
Surya Siddhanta	An ancient Indian astronomical text written in Sanskrit that provides calculations to predict eclipses.
Transit of Venus	A rare event where Venus passes between the Sun and the Earth, appearing as a tiny black dot passing against the bright face of the Sun.