The eclipse of the moon occurs when?

Analysis of the Question

This question tests your understanding of rectilinear propagation of light and the relative positions of celestial bodies (the Sun, the Earth, and the Moon) during an eclipse.

Concept Explanation

An eclipse occurs when one celestial body moves into the shadow of another.

• Solar Eclipse: Occurs when the Moon passes between the Sun and the Earth, casting a shadow on the Earth.
• Lunar Eclipse (Eclipse of the Moon): Occurs when the Earth passes directly between the Sun and the Moon. Because the Earth is opaque, it blocks the sunlight that would normally reach the Moon, casting a shadow on the Moon's surface.

Step-by-Step Solution

1. Identify the components: We have the Sun (the light source), the Earth, and the Moon.
2. Analyze the condition for a Lunar Eclipse: For the Moon to be "eclipsed" (darkened), the light from the Sun must be obstructed by an object.
3. Determine the positioning: If the Earth moves into the path of the light rays traveling from the Sun toward the Moon, the Earth will cast a shadow on the Moon.
4. Evaluate the options: • Option A describes the normal state of the Moon (reflecting sunlight), not an eclipse. • Option B describes a Solar Eclipse. • Option C describes the Earth blocking the Sun's light from reaching the Moon, which is the definition of a Lunar Eclipse. • Option D is physically impossible in this context, as the Sun is the source of light.

Conclusion

The Earth must be positioned exactly between the Sun and the Moon to block the light and create a lunar eclipse. This matches option C.

Exam Tip

To remember the difference, look at the name of the eclipse:

• Lunar Eclipse: The Moon is the one being hidden (Lunar = Moon). The Earth is in the middle.
• Solar Eclipse: The Sun is the one being hidden (Solar = Sun). The Moon is in the middle.