LUNAR ECLIPSE AND RED MOON

Edited-30-september-2015

Total Lunar Eclipse

During a total lunar eclipse, the Sun, Earth and Moon form a straight line. The Earth blocks any direct sunlight from reaching the Moon. The Sun is behind the Earth, so the Sun's light casts the Earth's shadow on the Moon. This shadow covers the entire Moon and causes a total lunar eclipse.

The figure shown above shows the shadow of the earth on the moon . Umbra a conical shaped shadow made by earth along with it a different visualization of shadow shows penumbra . Don't be confuse with these terminology as you can observe the rays which are tangent to both sun and earth on same side creating Umbra shadow . And those rays tangent to both sun and earth but in opposite sides creating  Penumbra shadow.  

The Moon does not have any light of it's own – it shines because its surface reflects sunlight. During a total lunar eclipse, the Earth moves between the Sun and the Moon and cuts off the Moon's light supply. When this happens, the surface of the Moon takes on a reddish glow instead of going completely dark. Also the Moon appears dark until earth's shadow covers it completely .

The red color of a totally eclipsed Moon has prompted many people in recent years to refer to total lunar eclipses as Blood Moons.

Why Red?

The reason why the Moon takes on a reddish color during totality is a phenomenon called Rayleigh scattering. It is the same mechanism responsible for causing colorful sunrises and sunsets and the sky to look blue. Rayleigh law is based on the fact that if white light is falling on a particle whose particle size is much much less than the wavelength of incident light so the light will scattered in all direction in splitting pattern into its constituents VIBGYOR . As Rayleigh says the intensity of scattered light is inversely proportional to fourth power of wavelength of different lights . Let say wavelength of RED color is large so it will scattered least . And for violet its wavelength in small so it will scattered high . Means visibility of red color for longer distance is more . That's why light pass through the earth atmosphere it scattered according to the Rayleigh when light reach us after reflection from the moon only red color reach to us . 

Colorful Sunlight

We all know from our school science textbooks that even though sunlight may look white to human eyes, it is actually composed of different colors. These colors are visible through a prism or in a rainbow. Colors towards the red spectrum have longer wavelengths and lower frequencies compared to colors towards the violet spectrum which have shorter wavelengths and higher frequencies.

Earth's Atmosphere

The next piece in the puzzle of why the sky looks blue and a totally eclipsed Moon turns red is the Earth's atmosphere. The atmosphere is about 300 miles (480 kilometers) thick and is made up of different gases, water droplets and dust particles.

When sunlight entering the Earth's atmosphere strikes the particles that are smaller than the light's wavelength, it gets scattered. Not all colors in the light spectrum, however, get equally scattered. Colors with shorter wavelengths, for example those towards the violet spectrum, are scattered more strongly than those with longer wavelengths like red and orange, which pass through the atmosphere. This light then gets bent or refracted back to the surface of the Moon and gives it the reddish-orange glow that total lunar eclipses are famous for.

Look for a Blue Band

Veteran eclipse watchers will tell you that if you look really hard right at the beginning and just before the end of totality, you may detect a light blue band on the Moon's face. This happens because the Earth's Ozone Layer scatters red light and lets through some of the blue light that gets refracted to the Moon.

We must have to understand the reason why some time moon appears blue around its ring along with red during lunar eclipse. As you can observe in the figure the rays those refracted from the outer atmosphere means 12 kilometer above the sea level results blue appearance . In figure you can see two rays both are white but after refraction they are showing different color . These are just representation . The ray which refract from 12 km above sea level will bring you the blue appearance of the moon reason is that the Ozone layer absorbs the orange , red light and offers least scattering because at height the density of atmosphere is less , so when that ray reflected from the surface of the moon and reached our eye it's Blue color intensity retained  , which results in blue appearance.

Sunbeams change their color as they pass through the earth atmosphere and refract into the umbra. The upper beam turns blue because orange light is absorbed by ozone when passes through the stratosphere. The lower beam, which refracts more due to denser earth atmosphere, turns red because short wavelength are scattered more thoroughly as the beam passes through denser troposphere. (source: Stanley David Gedzelman)

Please observe the image above carefully and see the blue  appearance on the moon.  

Many Shades of Red

The Moon can take on different shades of red, orange or gold during a total lunar eclipse, depending on the conditions of the Earth's atmosphere at the time of the Eclipse. The amount of dust particles, water droplets, clouds and mist can all have an effect on the shade of red. Volcanic ash and dust in the atmosphere can also lead to the Moon turning dark during an eclipse. In December 1992, not long after the eruption of Mount Pinatubo in the Philippines, there was so much dust in Earth’s atmosphere that the totally eclipsed moon could barely be seen.

What happened if there is no atmosphere on the earth?

If Earth didn’t have an atmosphere, then, when the moon was entirely eclipsed within Earth’s shadow, the moon would would appear dark …