The earth revolves round the sun in an elliptical orbit. Its speed

Options

A. goes on decreasing continuously
B. greatest when it is closest to the sun
C. greatest when it is farthest from the sun
D. constant at all the points on the orbit

Answer

To solve the problem regarding the speed of the Earth as it revolves around the Sun in an elliptical orbit, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Orbit**:
The Earth's orbit around the Sun is elliptical, which means it has two focal points, one of which is occupied by the Sun. The distance between the Earth and the Sun varies as the Earth moves along its orbit.

**Hint**: Remember that an elliptical orbit has varying distances from the focal point (the Sun) at different points along the path.

2. **Kepler's Laws of Planetary Motion**:
According to Kepler's second law (the law of areas), a line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time. This implies that the speed of the planet (Earth) changes depending on its distance from the Sun.

**Hint**: Kepler's laws are crucial for understanding the motion of planets in elliptical orbits.

3. **Speed Variation**:
- When the Earth is closest to the Sun (at perihelion), it moves faster because it sweeps out a larger area in the same amount of time.
- Conversely, when the Earth is farthest from the Sun (at aphelion), it moves slower because it sweeps out a smaller area in the same time.

**Hint**: Visualize the elliptical orbit and think about how the area swept out relates to speed.

4. **Analyzing Speed**:
- At perihelion (closest point), the speed is maximum.
- At aphelion (farthest point), the speed is minimum.
- Therefore, the speed of the Earth is not constant; it varies based on its position in the orbit.

**Hint**: Consider how the gravitational force from the Sun affects the speed of the Earth at different distances.

5. **Conclusion**:
Based on the analysis, the correct statement is that the speed of the Earth is greatest when it is closest to the Sun and least when it is farthest from the Sun.

**Hint**: Look for options that reflect this relationship between distance and speed.

### Final Answer:
The speed of the Earth is greatest when it is closest to the Sun (perihelion) and least when it is farthest from the Sun (aphelion). Therefore, the correct option is that the speed is maximum at the closest distance to the Sun.