Rainbows and Rain on Lunar Eclipse

Rainy Days and Nights make for a spectacular Rainbow and a non-eventful Lunar Eclipse (Oct 8 2014)

Early Wednesday morning – (meaning 3 am local time for us) was a wash-out for the Oct 8 2014 Lunar Eclipse. I awoke to the sound of heavy rain, and gladly went back to sleep to the sound of pitter-patter on the windowsill. However for eclipse enthusiasts, this was a disappointment, and their recourse is to visit October 2014_lunar eclipse. You may have seen reference to an eclipse as a ‘Blood moon’ due to the moon’s orange or red-ish color  when it is totally within the Earth’s shadow during the eclipse.

“Blood moon” during eclipse caused by Refraction of sunlight

‘ The Moon does not completely disappear as it passes through the umbra because of the refraction of sunlight by the Earth’s atmosphere into the shadow cone; if the Earth had no atmosphere, the Moon would be completely dark during an eclipse.The red coloring arises because sunlight reaching the Moon must pass through a long and dense layer of the Earth’s atmosphere, where it is scattered. Shorter wavelengths are more likely to be scattered by the air molecules and the small particles, and so by the time the light has passed through the atmosphere, the longer wavelengths dominate. This resulting light we perceive as red. This is the same effect that causes sunsets and sunrises to turn the sky a reddish color ‘ – courtesy Wikipedia Understanding lunar eclipse appearance


Courtesy http://cimss.ssec.wisc.edu/wxwise/class/optics.html

In a full lunar eclipse the Sun, Earth and Moon line up and the Earth casts its shadow on the Moon. As light passes through the atmosphere, the blue colors are scattered out of the path. Red and orange light passes through the atmosphere and is refracted (bent) into the shadow zone.

Courtesy – Astronomy Third Edition, (p 121), by Jay M. Pasachoff


courtesy http://nzsm.webcentre.co.nz/article1700.htm
courtesy http://nzsm.webcentre.co.nz/article1700.htm

Refraction of Sunlight – Rainbows are another natural example of this phenomena:

A triangular prism, dispersing light; waves shown to illustrate the differing wavelengths of light. - courtesy http://commons.wikimedia.org/wiki/File:Light_dispersion_conceptual_waves.gif
A triangular prism, dispersing light; waves shown to illustrate the differing wavelengths of light. – courtesy http://commons.wikimedia.org/wiki/File:Light_dispersion_conceptual_waves.gif


Spectrally Spectacular Blakeney

Just four days before, on Saturday Oct 4 2014,  after a  rainy afternoon, I took a spin down to the river at Blakeney and was treated to a rain-drenched sunset and double rainbow. (See last image).

After such a dreary day this was a welcome ‘Phos Hilarion’ or  Gladsome Light!

Here we can see the visual results of sunlight refracted, reflected and refracted through the medium of  water droplets, and separated into different colours based on how the wavelength components are bent through different angles.

Images courtesy P. Browne (Sat Oct 4 2014)
courtesy .weather.gov.hk/education/edu06nature/ele_rainbow_e.htm




Double Rainbow – notice the colour inversion. The ‘double’ in this case really refers to a double reflection inside the raindrop.


The above shows the Double Rainbow (with the secondary on the left). Notice too how the sequence shows a nearly semicircular shape from horizon to horizon. This shape is a result of the time at which the observer is viewing the rainbow. Since rainbows are formed opposite the Sun (I’m looking East at sunset), when the sun is sinking below the horizon the rainbow is reflecting that hemisphere of the sun above the horizon. Earlier would have made for a shallower arc.

What causes the prismatic nature of the rainbow?

When light passes through a water droplet, it gets refracted, reflected and then refracted again. The rainbow which we normally see (i.e. primary rainbow) results from one reflection inside a droplet. A secondary rainbow is produced when there are two reflections inside a droplet. – courtesy http://www.weather.gov.hk/education/edu06nature/ele_rainbow_e.htm




Identifying ROYGB(IV) Red Orange Yellow Green Blue... and maybe Indigo and violet...
Identifying ROYGB(IV)
Red Orange Yellow Green Blue… and maybe Indigo and violet…


We may not have had a ‘blood’ red lunar eclipse, but we did have a ‘ double’  rainbow. A total lunar eclipse  shows the red and longest wavelength of  spectral components and the rainbow shows the full electromagnetic spectrum thanks to the property of refraction and reflection!



visible Images – courtesy – “the electromagnetic spectrum” http://science.hq.nasa.gov/kids/imagers/ems/visible.html 

For more information on Stars and their Spectra – see http://millstonenews.com/2014/03/stars-in-our-milky-way-galaxy.html