In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.
Q: Article: Many people are aware of the beauty of a solar eclipse , but are surprised to learn that lunar eclipses are often just as impressive. While total solar eclipse lasts only for a few minutes and can be seen only in a small area of a few kilometers, total lunar eclipse can last for several hours and can be seen over much of the planet. In fact, the beauty and _ of lunar eclipses make them a favorite of both amateur and professional photographers. Lunar eclipses generally occur two or three times a year, and are possible only when the Moon is full. When we see the Moon, we are actually seeing sunlight reflected off the surface of the Moon When the Earth is positioned in between the Moon and the Sun, however, the Earth's shadow falls on the Moon, and a lunar eclipse occurs. The type of lunar eclipse - total, partial, or penumbral - that occurs depends both on how much of the Moon passes through the Earth's shadow and through which part of the shadow it passes. A penumbral eclipse occurs when the Moon passes through the Earth's outer shadow. This type of eclipse is brief and frequently goes unobserved by all but astronomers. By contrast, total and partial eclipses occur when all or part, respectively, of the Moon passes through the umbra shadow of the Earth. These eclipses are quite easy to see and are widely observed. Unlike solar eclipses, lunar eclipses are safe to watch. Solar radiation that occurs during an eclipse of the Sun can cause a form of burns of one's eyes known as eclipse blindness. In fact, the only way to safely view a solar eclipse is by using specially designed equipment. However, since the Moon's light is reflected sunlight, it is completely safe to watch a lunar eclipse without any special equipment, although a pair of binoculars can certainly help the viewer appreciate the beauty of this phenomenon
Answer: when only a part of the Moon passes through the Earth's umbra shadow
A:
According to the passage, a partial lunar eclipse occurs _ .