Penumbral Lunar Eclipse

A penumbra refers to a partially shaded outer region of a shadow that an object casts. A penumbral eclipse occurs when the moon passes through the faint penumbral portion of the earth’s shadow. The lunar surface is not completely shadowed by the earth’s umbra (darkest part of a shadow). Instead, observers see only the slightest dimming near the lunar limb closest to the umbra. The eclipse may be undetectable unless at least half of the moon enters the penumbra.
Tonight, February 9, the full Moon will pass through the outskirts of Earth’s shadow, producing a penumbral lunar eclipse. The event will be visible to the naked eye as a dusky shading of the northern half of the Moon. According to NASA, this event is the deepest penumbral eclipse in 2009, with a penumbral magnitude of 0.899.