text: when does a lunar eclipse occur?   an eclipse of the moon (or lunar eclipse) can only occur at full moon, and only if the moon passes through some portion of the earth's shadow.   1. penumbral lunar eclipse   the moon passes through earth's penumbral shadow.  these events are of only academic interest since they are subtle and quite difficult to observe.  2. partial lunar eclipse   a portion of the moon passes through earth's umbral shadow.  these events are easy to see, even with the unaided eye.  3. total lunar eclipse   the entire moon passes through earth's umbral shadow.  these events are quite striking for the vibrant range of colors the moon can take on during the total phase (i.e. - totality).