The main source of sun.s energy is

Options

A. Nuclear fusion
B. Nuclear fission
C. Gravitational contraction
D. Combustion

Answer

To solve the question regarding the main source of the sun's energy, we will analyze the given options step by step.

### Step-by-Step Solution:

1. **Identify the Options**: The options provided are:
- Nuclear Fusion
- Nuclear Fission
- Gravitational Contraction
- Combustion

2. **Understand Each Option**:
- **Nuclear Fusion**: This is a process where two light atomic nuclei combine to form a heavier nucleus, releasing a significant amount of energy.
- **Nuclear Fission**: This involves splitting a heavy nucleus into lighter nuclei, which also releases energy but is not the primary process in the sun.
- **Gravitational Contraction**: This refers to the process where a mass contracts under its own gravity, which can lead to heating but is not the main source of energy in the sun.
- **Combustion**: This is a chemical reaction that typically involves burning, which is not the process that powers the sun.

3. **Focus on Nuclear Fusion**:
- In the core of the sun, conditions are extremely hot (about 15 million degrees Celsius) and under immense pressure. Under these conditions, hydrogen nuclei (protons) collide and fuse to form helium nuclei.
- This fusion process releases a tremendous amount of energy in the form of light and heat, which is what we perceive as sunlight.

4. **Conclusion**:
- Given that nuclear fusion is the process that occurs in the sun's core and is responsible for producing energy, we can conclude that the main source of the sun's energy is **Nuclear Fusion**.

### Final Answer:
The main source of the sun's energy is **Nuclear Fusion**.