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๐ฌ Think about it
Here's the twist: the Moon's shape never actually changes — only how much of its sunlit side we can see. Hold a ball near a lamp and walk around it, and you'll see the same effect. Let's make sense of the phases.
Why does the Moon's bright shape seem to change?
- The Moon's own shape does not change — only what we see.
- The half facing the Sun is lit; the other half is dark.
- The Moon orbits Earth, so we see different amounts of its lit half.
- On new Moon, only the dark half faces Earth.
Example:
When only part of the lit half faces us, the Moon looks like a crescent or half circle.
In this Activity, we will use a ball and a lamp to model how the Moon's phases form.
Materials needed
A small soft ball, a stick, a torch or an electric lamp, a dark open place.
Procedure
1. Insert a stick into the ball; this represents the Moon.
2. In the dark, have an adult shine a torch from about 3 m, representing the Sun. Your head is the Earth.
3. Hold the ball at arm's length, slightly above your head, towards the lamp (position E).
4. Check if the side facing you looks lit or not.
5. Turn slowly anti-clockwise, watching how the lit portion changes.
6. Notice the curved line dividing the lit and dark parts.
2. In the dark, have an adult shine a torch from about 3 m, representing the Sun. Your head is the Earth.
3. Hold the ball at arm's length, slightly above your head, towards the lamp (position E).
4. Check if the side facing you looks lit or not.
5. Turn slowly anti-clockwise, watching how the lit portion changes.
6. Notice the curved line dividing the lit and dark parts.
Observation
When the ball is opposite the lamp (A), the whole lit side faces you, like a full Moon. When the ball is towards the lamp (E), you see only the dark side, like a new Moon. In between, the lit part looks curved.
Explanation
The shape of the lit portion you see changes with the ball's position relative to the lamp — exactly how the Moon's phases form as it orbits the Earth.
โ Summary
- Ball is the Moon
- Lamp is the Sun
- Head is the Earth
- Phases appear
What are the gibbous and crescent phases?
- The part of the Moon facing Earth is only partly lit on most days.
- Gibbous phase: more than half the lit portion is seen.
- Crescent phase: less than half the lit portion is seen.
- From new to full Moon we see waxing; from full to new, waning.
Gibbous phase
Crescent phase
More than half the lit part is seen.
Less than half the lit part is seen.
Close to a full Moon.
Close to a new Moon.
Why does the Moon shift position at the same time each day?
- The Earth rotates once in 24 hours.
- Meanwhile the Moon moves ahead in its orbit.
- So Earth must rotate a little more to face the Moon again.
- This makes the Moon appear about 50 minutes later each day.
Example:
If the Moon is overhead today at a set time, tomorrow it reaches there about 50 minutes later.
๐ก A step further
- Moon phases are not caused by Earth's shadow.
- Phases come from the changing Sun–Moon–Earth orientation.
- Earth's shadow on the Moon causes a lunar eclipse instead.
- Lunar eclipses happen only on full Moon, solar eclipses on new Moon.
Important Points
- The Moon's shape doesn't change — only the lit part we see does.
- Gibbous shows more than half lit; crescent shows less than half.
- The Moon appears about 50 minutes later each day.
โ Test Yourself
-
Does the Moon's actual shape change?
View Answer
No. Only the amount of its sunlit half that we see from Earth changes. -
Why is the Moon invisible on new Moon day?
View Answer
Only the non-illuminated (dark) half of the Moon faces the Earth, so we see no bright part. -
What is the gibbous phase?
View Answer
When more than half of the Moon's lit portion is seen from Earth. -
What really causes a lunar eclipse?
View Answer
The Earth's shadow falling on the Moon — not the cause of the Moon's phases. -
Why does the Moon appear about 50 minutes later each day?
View Answer
The Moon moves ahead in its orbit, so the Earth must rotate a bit more to face it again.
Important Definitions
- Illuminated portion — the half of the Moon facing the Sun, which receives sunlight.
- Gibbous phase — when more than half the lit portion of the Moon is seen from Earth.
- Crescent phase — when less than half the lit portion of the Moon is seen from Earth.
๐ NCERT Question 1 — State whether the following
Decide whether statements about the Moon, phases, and calendars are true or false.
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๐ NCERT Question 3 — Name two things that
Name two things that are incorrect in the picture of a crescent Moon among clouds and stars.
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๐ NCERT Question 5 — Malini saw the Moon
Malini saw the Moon overhead at sunset. Draw the phase and say if it is waxing or waning.
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๐ NCERT Question 6 — Ravi said, "I saw
Ravi and Kaushalya each describe seeing the Moon. Who is telling the truth?
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๐ NCERT Question 9 — On a particular night,
Vaishali saw the Moon all night from sunset to sunrise. What phase was it?
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