Why does the Moon appear Red during a Lunar Eclipse?

WE EXPERIENCED a lunar eclipse last night, June 15, 2011. Unfortunately, due to cloudy skies, we failed to witness the moon turn into a reddish glowing sphere in the night sky. It should have been an amazing spectacle.

Lunar_Eclipse_by_Jiyang_Chen

 

But why does the moon look red during a lunar eclipse?

A lunar eclipse happens when the Earth is between the Moon and the Sun. The Sun is the source of light and the Earth happens to block it so that light coming from the Sun does not directly hit the Moon.

Light rays from the Sun appear white because it is a combination of all the colors of light in the visible spectrum.

electromagnetic-spectrum
The waves are arranged in decreasing wavelength and increasing frequency.

 

When Sun’s light enters the Earth’s atmosphere, each region of the spectrum travels at different speed. As each light wave’s speed changes, the direction it is headed to also changes. In other words, they bend as they enter the Earth’s atmosphere, but the angle of their bending varies.

Simply put, the light waves are being scattered by the particles in the Earth’s atmosphere. The light waves that have shorter wavelengths are scattered to a higher degree compared to those with longer wavelengths. Because red, orange, and yellow light waves are not scattered very much, these are the waves that appear to be permitted and reach the surface of the moon.

Here is an animated gif image I created using Adobe CS3 to explain the phenomenon:

lunar-eclipse animation

 

Here is another illustration and explanation from Wikipedia:

Lunar_eclipse_optics

 

Curious about other physical phenomena? Ask the Teacher!

ask the teacher

Ariel Lalisan

Ariel Lalisan

Ariel Lalisan is a physics teacher at Alabel National Science High School. He is an advocate of constructivism approach in education. He employs active learning and independent learning in his lessons, and, of course, a lot of technology integration. His goal is to produce students who can solve problems on their own using the concepts they learn in the classroom. Ariel Lalisan is a Google Certified Innovator (Google Teachers Academy Southeast Asia 2014) and a community leader at Google Educator Group Sarangani. He is a co-founder of SoCCSKSarGen and he won the Globe Media Excellence Blogger of the Year Award in 2015.

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5 thoughts on “Why does the Moon appear Red during a Lunar Eclipse?

    1. If you would look at the last illustration (that one from Wikipedia), the moon would look red if it is in that position (the center). Otherwise, it would look like it usually does (bright gray).

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