The colour of a star indicates its

Options

A. temperature
B. distance
C. velocity
D. size

Explanation

To solve the question "The colour of a star indicates its...", we will analyze the relationship between the color of a star and its properties, particularly focusing on temperature.

### Step-by-Step Solution:

1. **Understanding Star Color**:
- Stars emit light of various colors, which can be observed from Earth. The color of a star is primarily determined by the temperature of its surface.

2. **Wien's Displacement Law**:
- According to Wien's Displacement Law, the wavelength (λ) of the emitted radiation is inversely proportional to the temperature (T) of the star. This means that as the temperature increases, the wavelength of the emitted light decreases.
- Mathematically, this can be expressed as:
\[ \lambda_{\text{max}} = \frac{b}{T} \]
where \( b \) is Wien's displacement constant.

3. **Color and Temperature Relationship**:
- Different temperatures correspond to different colors of light. For example:
- Hotter stars (higher temperature) emit light that appears blue or white.
- Cooler stars (lower temperature) emit light that appears red or orange.
- This is consistent with the visible spectrum, where the sequence of colors from high to low energy is violet, indigo, blue, green, yellow, orange, and red.

4. **Conclusion**:
- Therefore, the color of a star is a direct indicator of its temperature. A blue star is hotter than a red star, and this relationship allows astronomers to estimate the surface temperature of stars based on their color.

### Final Answer:
The color of a star indicates its **temperature**.

---