An astronomical telescope has large apeture to

Options

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

Answer

### Step-by-Step Solution:

1. **Understanding the Components of an Astronomical Telescope**:
- An astronomical telescope consists of two main lenses: the objective lens and the eyepiece. The objective lens is larger, while the eyepiece is smaller.

2. **Purpose of the Objective Lens**:
- The objective lens is designed to collect light from distant celestial objects. Since these objects are very far away (often considered to be at infinity), the amount of light reaching the telescope is minimal.

3. **Importance of a Large Aperture**:
- A larger aperture (the diameter of the objective lens) allows the telescope to gather more light. This is crucial for observing faint objects like stars and galaxies, which emit very little light.

4. **Resolution and Clarity**:
- A larger aperture not only gathers more light but also improves the resolution of the images produced. Higher resolution means that the telescope can distinguish finer details of the celestial objects being observed.

5. **Conclusion**:
- Therefore, the primary reason an astronomical telescope has a large aperture is to achieve high resolution by collecting maximum light from distant celestial objects.

### Final Answer:
The astronomical telescope has a large aperture to achieve high resolution.