If a star is moving towards the earth, then the lines are shifted towards

Options

A. red
B. infra-red
C. blue
D. green

Answer

To solve the question, we need to understand the concept of the Doppler effect as it applies to light. When a star is moving towards the Earth, the light waves emitted by the star are compressed, leading to a shift in the observed wavelength of light. Here’s a step-by-step solution:

### Step-by-Step Solution:

1. **Understanding the Motion of the Star**:
- When a star moves towards the Earth, it is approaching the observer located on Earth.

2. **Effect on Light Waves**:
- As the star approaches, the light waves emitted by it are compressed. This means that the distance between successive wavefronts decreases.

3. **Change in Frequency**:
- The compression of the light waves results in an increase in the frequency of the light. According to the wave equation, frequency (f) and wavelength (λ) are inversely related: \( c = f \cdot \lambda \), where \( c \) is the speed of light.

4. **Change in Wavelength**:
- Since the frequency increases, the wavelength must decrease. This is because as the frequency goes up, the wavelength must go down to keep the speed of light constant.

5. **Understanding the Spectrum**:
- The visible spectrum ranges from red (longer wavelengths) to violet (shorter wavelengths). A decrease in wavelength means that the light shifts towards the blue end of the spectrum.

6. **Conclusion**:
- Therefore, if a star is moving towards the Earth, the lines in the spectrum of the light emitted by the star will shift towards the blue end. This phenomenon is known as "blueshift."

### Final Answer:
The lines are shifted towards the **blue** end of the spectrum.

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