Final answer:
A solar eclipse happens when the Moon passes between Earth and the Sun, casting its shadow on Earth. During a total solar eclipse, the Moon's umbra touches the Earth, fully blocking the Sun. In contrast, a lunar eclipse occurs when the Moon enters Earth's shadow.
Step-by-step explanation:
A solar eclipse occurs when the Moon's shadow is cast on Earth. This happens when the Moon moves between the Sun and Earth, blocking the light of the Sun from a portion of Earth's surface. If the Moon is at a certain distance where it completely covers the Sun, a total solar eclipse occurs, and the umbra (the darkest part of the shadow) touches the Earth.
The Sun and Moon appear to be nearly the same size from our perspective on Earth, which is why the Moon can block the Sun so precisely during a solar eclipse. However, a lunar eclipse happens when the Moon passes into Earth's shadow, which is visible from the entire night side of Earth.