# Our Sky

## Overview

In this chapter, students explore how the sky changes at different times of the day. They observe how sunlight affects the sky’s color, shapes of shadows, and the appearance of the Moon and stars. The chapter also introduces cultural aspects such as festivals based on moon phases and historical tools like the sundial.

## Key Topics Covered

### 1. Changes in the Sky

- The sky looks different in the **morning**, **afternoon**, and **night**.
- The **color of the sky** and **Sun’s brightness** change throughout the day.
- The **Moon’s size and shape** also change from day to day.
- Activities of humans, animals, and plants vary depending on the time of the day.

### 2. Observing the Sun

- The **Sun** is the brightest object in the sky.
- It appears to rise in the **East**, moves across the sky, and sets in the **West**.
- It provides **light and heat**.
- The Sun’s position affects what we see and do throughout the day.

### 3. Sunrise and Sunset Observations

#### During Sunrise:

- The sky becomes brighter with orange hues.
- Birds start chirping and animals become active.
- People begin their morning routines.

#### During Sunset:

- The sky shows red and orange colors.
- Birds return to their nests and animals prepare to rest.
- Lights are turned on at homes and the day winds down.

### 4. Understanding Shadows

- Shadows are formed when an object blocks light.
- They **change in size and direction** throughout the day:
- **Morning**: Long shadows
- **Noon**: Short shadows
- **Evening**: Long shadows in the opposite direction of morning
- You can experiment with shadows using a **torch and stick** to observe how distance and angle affect the shadow.

### 5. Movement of the Sun and Shadow Direction

- As the Sun appears to move across the sky, shadows change direction.
- **East → Overhead → West**: This movement creates predictable shadow patterns.
- Ancient people used shadows to tell time using a **sundial**.
- **Jantar Mantar** in India is a famous observatory that includes a large sundial called **Samrat Yantra**.

### 6. The Night Sky

- After sunset, the sky is filled with **stars**.
- Stars can form **patterns** or constellations.
- The **Moon** appears as the largest object in the night sky.

### 7. Phases of the Moon

- The Moon’s shape changes from night to night.
- These shapes are known as **phases**:
- **Full Moon (Poornima)** – complete round Moon.
- **New Moon (Amavasya)** – Moon is not visible.
- **Crescent Moon** – looks like the letter 'C'.
- **Half Moon** – Moon appears split in half.
- The Moon’s cycle was used by ancient people to track time and create early **calendars**.

### 8. Festivals Based on the Moon

- Many festivals in India are celebrated based on the appearance of the Moon:
- **Diwali** – on the new Moon (Amavasya).
- **Rakshabandhan**, **Guru Poornima**, **Buddha Poornima** – on the full Moon.
- **Eid** – on the first visible crescent after the new Moon.
- **Pongal**, **Chhath Puja**, **Karva Chauth** – linked with Sun or Moon.

### 9. India's Moon Mission

- On **23 August 2023**, India’s **Vikram Lander** of the **Chandrayaan Mission** successfully landed on the Moon.
- It studied the Moon’s surface and collected scientific data.

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## New Terms and Definitions

| Term | Simple Definition |
| ------------- | -------------------------------------------------------- |
| Sunrise | Time when the Sun comes up in the morning |
| Sunset | Time when the Sun goes down in the evening |
| Shadow | A dark shape made when an object blocks light |
| Sundial | A device that tells time using shadows |
| Full Moon | Night when the Moon appears completely round |
| New Moon | Night when the Moon is not visible |
| Constellation | A pattern or group of stars in the night sky |
| Festival | A special day of celebration often linked to Moon or Sun |
| Vikram Lander | Indian spacecraft that landed on the Moon |
| Jantar Mantar | Ancient observatory built to study space and time |

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## Practice Questions

### Easy (3)

1. **What is the brightest object in the sky during the day?**
**Answer**: The Sun.
**Explanation**: The Sun gives us light and heat during the day.

2. **What changes in the sky when the Sun sets?**
**Answer**: The sky becomes dark and stars appear.
**Explanation**: The Sun is no longer visible, so the stars become visible.

3. **What is a shadow?**
**Answer**: A shadow is a dark shape formed when an object blocks light.
**Explanation**: Shadows are seen because light cannot pass through objects.

### Medium (2)

4. **Why do shadows change direction during the day?**
**Answer**: Because the Sun appears to move across the sky.
**Explanation**: As the Sun moves, the angle of sunlight changes, causing the shadow to change direction.

5. **What is a full Moon called in Hindi?**
**Answer**: Poornima.
**Explanation**: It is the day when the Moon is completely visible in a round shape.

### Difficult (3)

6. **Why can we not see stars during the day?**
**Answer**: Because the Sun is too bright.
**Explanation**: The Sun’s brightness hides the light of stars during the daytime.

7. **Why does the Moon appear in different shapes?**
**Answer**: Because of its changing position with respect to the Earth and Sun.
**Explanation**: The part of the Moon we see is lit by the Sun and changes as the Moon moves.

8. **What does a sundial do?**
**Answer**: It tells time using shadows.
**Explanation**: The shadow's length and direction change with time and were used to track hours.

### Very Difficult (2)

9. **How do the phases of the Moon help in making a calendar?**
**Answer**: Each phase happens in a cycle, helping people count days and months.
**Explanation**: By observing these regular patterns, early people could track time.

10. **Why do animals behave differently during the day and night?**
**Answer**: Their activity is based on sunlight and natural rhythms.
**Explanation**: Some animals are active during the day (diurnal), others at night (nocturnal), depending on their nature.

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