‘Because a lot of light scatters off the Earth’s atmosphere, the moon will not look completely dark but have a coppery red color — hence the blood moon moniker’.
‘What’s actually happening is a confluence of three things. The moon will be full and in its closest point in its orbit around the Earth, making it a so-called supermoon’.
‘Supermoons appear 14% larger and 33% brighter than other full moons’.
‘In addition to this, a lunar eclipse will occur. In other words, the Earth will line up directly with the sun and moon, directly between the two, so the “moon will completely fall in the shadow of the Earth.”
From : http://www.usatoday.com/story/news/nation-now/2015/09/25/blood-moon-lunar-eclipse-super-moon-need-to-know/72790162/