A total lunar eclipse happens when the Moon goes into the Earths shadow. This can occur only when the Sun, Earth, and Moon are exactly or very closely aligned with Earth between the other two. Due to this reddish color, a totally eclipsed Moon is sometimes called a blood moon.
The red color is caused by Rayleigh scattering of sunlight through the Earth's atmosphere, the same effect that causes sunsets to appear red.
Rayleigh scattering is the way that light scatters when it hits a very small object. The theory is good if the wavelength of light is much bigger than the object. It is named after Lord Rayleigh. and it also mainly discovered by Raman as through Raman scattering.scatterings of sunlight through the Earth's atmosphere, the same effect that causes sunsets to appear red.