Science behind 'Super moon' and 'Blood moon'

On 27th and 28th September 2015, we witnessed the celestial phenomena of   "Super Moon" and the  "Blood Moon". And before people fall prey to various speculations and superstitions, let me put before them what science says about them.

A Super moon is a phenomenon that occurs when a full or new Moon coincides with a Moon that is nearing its minimum distance (perigee) to Earth. The Moon takes an elliptical orbit around Earth, which means that the average distance between the two changes from as much as 405,000km (its apogee) to as low as 363,000km at the perigee. Simply put, the Supermoon occurs when the Moon is at its closest to the Earth. The phenomenon can make the Moon appear larger by nearly 14 times its usual visible size and it appears very bright too.

As for the beautiful blood red colour we saw, here’s explanation for the same: During a total lunar eclipse, white sunlight hitting the atmosphere on the sides of the Earth gets absorbed and then radiated out (scattered). That is, the atmosphere filters out (scatters away) most of the blue-colored light... what’s left is the orange- and red-coloured light. This red coloured light passes through our atmosphere without getting absorbed and scattered, before the atmosphere bends it (refracts it) back out, projecting indirect, reddish light on to the Moon. The reddish light projected on the Moon is dimmer than the full white sunlight that the Moon typically reflects back to us. That’s because the light is indirect and because the red-coloured wave lengths are only part of what makes up the white light from the Sun that the Moon usually receives.

The reason why the Moon turns red during a total lunar eclipse is related to why we have such beautiful pink, orange and red sunrises and sunsets to enjoy. When we see a sunrise or sunset from our perspective on Earth, sunlight is coming in at a low angle. It has to travel through a lot of atmosphere, scattering more and more blue-colored light as it goes... until what is left when the light reaches us at these day/night transition times is the more reddish wavelengths that get through. You’re basically seeing all of the sunrises and sunsets across the world, all at once, being reflected off the surface of the Moon.

Observers on Earth may see a Moon that is brick-coloured, rusty, blood red or sometimes dark grey, depending on terrestrial conditions. Here in India, we didn't actually see red blood coloured moon on Monday but a very pale tinge of orange appeared on its very bright surface.

Picture credit: Reuters