Chandra Grahan In May 2023: Why Does Moon Appear Red On Lunar Eclipse?

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In astronomy, this celestial event holds immense significance, especially for enthusiastic stargazers, but in Hinduism, eclipses are seen as associated with inauspiciousness.

This year, the first Lunar Eclipse (Penumbral lunar eclipse) will begin on 05 May 2023 at 08: 44 pm IST and will end at 01:01 am IST on 6 May 2023. This will be visible in South/Eastern Europe, most of Asia, Australia, Africa, Pacific, Atlantic, Indian Ocean, and Antarctica. It will also coincide with Buddha Purnima.

The second lunar eclipse will happen on 28 October 2023 at 04:24 pm in Europe, Asia, Australia, Africa, North America, North/East South America, Pacific, Atlantic, Indian Ocean, Arctic, and Antarctica. However, the lunar eclipse will not be visible from India.

How Does Lunar Eclipse Work?
Lunar eclipses happen during the full moon phase when the Earth positions itself precisely between the Moon and the Sun. The Earth casts its shadow on the surface of the moon and dims it. Due to this, at times, the lunar surface appears striking red for the course of a few hours. There Are Three Different Types Of Lunar Eclipses - total lunar eclipse, partial lunar eclipse, and Penumbral eclipse.

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Lunar Eclipse In May 2023: Why Does Moon Appear Red On Chandra Grahan?
So, why does the moon appear red on Chandra Grahan? According to NASA, during a lunar eclipse, the Moon turns red when the sunlight reaches the Moon and passes through Earth's atmosphere. The more dust or clouds in the Earth's atmosphere during the eclipse, the redder the Moon will appear. It's as if all the world's sunrises and sunsets are projected onto the Moon.

While some colours like blue and violet have shorter wavelengths, the others like red and have longer wavelengths. Therefore, whenever, the Sun is overhead, the sky appears blue, but when the sun sets, we see colours like yellow, orange and red, which dominate the sky entirely. This phenomenon is known as Rayleigh scattering.

This same phenomenon occurs during lunar eclipse which makes the moon appear red. In a post on their website, NASA explains that light travels in waves, and therefore, different colours of light have distinct physical properties. 'Blue light has a shorter wavelength and is scattered more easily by particles in Earth's atmosphere than red light, which has a longer wavelength.'

Blue travels in shorter and smaller waves and therefore, it gets easily scattered by the particles and dust during sunset. The sunlight reaches us from low in the sky, and travels farther before it reaches our eyes. Consequently, it passes through more air and particles scattering and rescattering blue light many times, in numerous directions. This is the reason, it gets removed from the atmosphere, and only the red, orange and yellow colours which have larger wavelengths make it through.