Blood Moon

The Blood Moon is a layman’s terminology, meaning its a non scientific term, to describe the reddish-rusty appearance of the moon when it undergoes a lunar eclipse. There is another lesser known interpretation of this term as well, using to refer to four consecutive lunar eclipses observed from a single place on earth withing a period of two years. Naturally this is quite rare in itself as a single spot on earth generally experiences four-five lunar eclipses in a decade.

Why is the blood moon red in color?

As we explained, the blood moon earns its reputation only due to its strikingly beautiful reddish hue during an eclipse. But what exactly causes it to take on that color? The phenomenon behind is a simple one that can be understood with help of basic physical concepts.

Primary reason for a lunar eclipse is that the earth effectively blocks the light from Sun during its journey to the moon. With no light to reflect, the moon appears to be eclipsed in Earth’s shadow. A few lucky times, the orientations of earth and moon are aligned in such a way that they give rise to a blood moon. Our planet although is opaque in nature, the same cannot be said about its atmosphere. Due to scattering, blue light from sun is scattered in our atmosphere. This leaves the larger wavelength color: red to refract and effectively pass through our translucent atmosphere, creating a sort of cone shaped-rusty fringe as shown in below diagram.

As it turns out, the moon only passes through this fringe occasionally because of its size and proximity to earth. Direct sunlight from sun is still blocked by the earth, but the reddish light passing through its atmosphere bends to bath the moon in red color. To passionate astrophiles on earth this is visible as a spooky blood stained moon worthy of admiration.