Blood Moon total lunar eclipse

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What is blood moon?

• Blood Moon is not a scientific term, though in recent times it is being widely used to refer to a total lunar eclipse because a fully eclipsed Moon often takes on a reddish color.

• While the moon will be immersed in the earth’s shadow, the red wavelengths of sunlight filter through Earth’s atmosphere, falling on the moon’s surface.

• A total lunar eclipse happens when the Moon travels through the Earth’s umbra and blocks all direct sunlight from illuminating the Moon’s surface. 
• However, some sunlight still reaches the lunar surface indirectly, via the Earth’s atmosphere, bathing the Moon in a reddish, yellow, or orange glow.
• As the Sun’s rays pass through the atmosphere, some colors in the light spectrum—those towards the violet spectrum—are filtered out by a phenomenon called Rayleigh scattering (This is the same mechanism that causes colorful sunrises and sunsets). 
• Red wavelengths are least affected by this effect, so the light reaching the Moon’s surface has a reddish hue, causing the fully eclipsed Moon to take on a red color.
• Depending on the composition of the atmosphere, different parts of the light spectrum are filtered out, so the Moon may also look yellow, orange, or brown during a total lunar eclipse.
• The term Blood Moon is also sometimes used to refer to four total lunar eclipses that happen in the span of two years, a phenomenon astronomers call a lunar tetrad. 
• The eclipses in a tetrad occur about six months apart with five uneclipsed Full Moons between them.

• The 2014–2015 lunar tetrad gathered a lot of attention because of claims by some religious organizations that the eclipses in the tetrad were a sign of the end times.

• The current century 2001 to 2100 will have eight tetrads. 
• The first tetrad of the 21st century took place in 2003-2004, the second was in 2014–2015, and the next will be in 2032–2033.

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