Which one of the following methods is used to measure distance of a planet or a star from the earth?

Options

A. Echo method
B. Parallax method
C. Triangulation method
D. none of these

Explanation

To solve the question regarding the method used to measure the distance of a planet or a star from the Earth, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for a method to measure distances to celestial bodies like planets or stars from Earth.

2. **Identifying Common Methods**: There are several methods used in astronomy to measure distances to stars and planets, including:
- Parallax method
- Standard candles (like Cepheid variables)
- Redshift measurements
- Radar ranging (for nearby planets)

3. **Focusing on the Parallax Method**: The parallax method is specifically used for measuring distances to nearby stars. It involves observing the apparent shift in position of a star against a more distant background when viewed from different positions of Earth in its orbit around the Sun.

4. **Limitations of the Parallax Method**: It is important to note that the parallax method is effective only for stars that are relatively close to Earth, typically up to about 400 light years. Beyond this distance, the parallax angle becomes too small to measure accurately.

5. **Conclusion**: Based on the understanding of the methods and their applications, the correct answer to the question is the parallax method.

### Final Answer:
The method used to measure the distance of a planet or a star from the Earth is the **parallax method**.

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