Question: when does an eclipse of the moon occur

title: Lunar eclipse
text: A lunar eclipse occurs when the Moon passes directly behind the Earth into its umbra ( shadow ) . This can occur only when the sun , Earth , and moon are aligned ( in `` syzygy '' ) exactly , or very closely so , with the Earth in the middle . Hence , a lunar eclipse can occur only the night of a full moon . The type and length of an eclipse depend upon the Moon 's location relative to its orbital nodes . 

Answer: answer: A lunar eclipse occurs when the Moon passes directly behind the Earth into its umbra ( shadow ) ,  this only occurs  when the sun , Earth , and moon are aligned. Hence , a lunar eclipse can occur only the night of a full moon .
answer: A lunar eclipse occurs when the Moon passes directly behind the Earth into its umbra. This can occur only when the sun , Earth , and moon are aligned exactly , or very closely so , with the Earth in the middle which is only possible on the night of a full moon .