Final answer:
Lunar eclipses occur when the Earth is between the sun and the moon, causing the moon to pass through the Earth's shadow.
Step-by-step explanation:
The relative positions of the sun, Earth, and moon during a lunar eclipse occur when the Earth is directly between the sun and the moon. In this alignment, the moon passes into the Earth's shadow, which can be seen from anywhere on the night side of the Earth. The progression of a lunar eclipse is shown in Figure 4.24, where the moon moves through different parts of Earth's shadow during the eclipse. The full shadow, or umbra causes the total phase of the eclipse, and the partial shadow or penumbra causes the partial phases.
During a solar eclipse, the moon is directly between the sun and Earth, casting a shadow on Earth. When the Sun, moon, and Earth align perfectly in a straight line, the moon's umbra touches the Earth’s surface, and this alignment results in a total solar eclipse visible in a narrow path on Earth's surface. Those in the wider area of the penumbra experience a partial solar eclipse. The geometry of a solar eclipse and the varying visibility, including total and partial eclipses, have been detailed in Figure 4.22.
Differences in apparent size due to the variable distances from Earth explain why some eclipses are total, while others are annular. In an annular eclipse, the moon appears smaller and does not completely cover the Sun, leaving a ring of light visible around the moon, as described in the reference material.