On Friday, a “blood moon” captivated eclipse-watchers in large parts of the world. Not only was it the century’s longest total lunar eclipse, it also happened when Mars was at its closest to Earth, and the Red Planet was also visible near the red Moon. But why was the Moon red?
This happens during any total lunar eclipse, because of the nature of sunlight and the positioning of the celestial bodies. Sunlight is made of different colours, from violet and blue (low wavelength) to red and orange (high wavelength). When sunlight enters the Earth’s atmosphere, these colours get scattered in different directions. During a lunar eclipse, the Earth comes between the Sun and the Moon, which means that it blocks light from getting between them. Any sunlight that does reach the Moon, therefore, has to make its way around the Earth. The light that manages to do so is that with the higher wavelengths, towards the red end of the spectrum. When this light hits the surface of the Moon, it gives it the reddish-orange glow that characterise a total lunar eclipse.
Although this has always been the case, the phrase “blood moon” is relatively new. Ed Krupp, director of the Griffith Observatory in Los Angeles, told The New York Times that the term was coined by evangelical ministers. It appears to have originated in 2008 when Mark Biltz, founder of El Shaddai Ministries in Washington State, said he had discovered a pattern among the lunar and solar eclipses that would signal the second coming of Christ. In 2013, megachurch pastor John Hagee prophesied in the book Four Blood Moons: Something Is About to Change that a series of four lunar eclipses within an 18-month span would precede the rapture, the NYT article said. Although the apocalypse did not arrive, “now every total lunar eclipse is called a blood moon,” the article quoted Krupp as saying.