Penumbral Lunar Eclipse
Penumbral Lunar eclipse happens when the Sun, Earth, and Moon are imperfectly aligned. During the penumbral lunar eclipse, the outer shadows of Earth, called penumbra covering parts or the whole surface of the Moon, however, it is often difficult to be seen by the naked eye. The penumbra shadows are much fainter than the umbra-the Earth’s inner shadows which is much darker. For this eclipse to happen the Moon must be in the Full Moon phase and the Sun, Earth, and Moon are nearly aligned but not as closely aligned during the partial eclipse. The penumbral eclipse involves the darker part of the penumbra, normally visible to the naked eye. A careful observer usually can see the penumbral eclipse while others see nothing.
Illustration retrieved from timeanddate.com