Large aperture of telescope are used for

Options

A. reduced spherical aberration
B. have high resolution
C. increase span of observation
D. have low dispersion

Explanation

To answer the question about why large apertures of telescopes are used, we can break down the reasoning step by step.

### Step-by-Step Solution:

1. **Understanding Resolving Power**:
- The resolving power (R) of a telescope is its ability to distinguish between two closely spaced objects. It is a crucial factor in determining how clear and detailed the images produced by the telescope will be.

2. **Relationship Between Aperture and Resolving Power**:
- The resolving power of a telescope is directly proportional to the diameter of the aperture (D) and inversely proportional to the wavelength of light (λ). This relationship can be expressed as:
\[ R \propto \frac{D}{\lambda} \]
- This means that as the diameter of the aperture increases, the resolving power also increases, provided that the wavelength of light remains constant.

3. **Implications of a Larger Aperture**:
- A larger aperture allows the telescope to collect more light, which not only enhances the brightness of the image but also improves the ability to resolve finer details. This is particularly important for observing distant celestial objects.

4. **Conclusion**:
- Therefore, the primary reason for using a large aperture in telescopes is to achieve higher resolution. This allows astronomers to observe and distinguish between objects that are very close together in the sky.

5. **Evaluating Options**:
- When considering the options given in the question:
- **Reduce spherical aberration**: This is not the correct reason for using a large aperture.
- **Have higher resolution**: This is the correct reason for using a large aperture.

### Final Answer:
Large apertures of telescopes are used to achieve higher resolution.

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