Via Earthsky.org: The origin of the term is religious, at least according to Christian pastor John Hagee, who wrote a 2013 book about Blood Moons.
Meanwhile, both astronomers and some proponents of Christian prophesy are talking about the upcoming lunar tetrad – the series of four total lunar eclipses – beginning on the night of April 14-15.
Other times in astronomy you hear “moon” and “blood” in same sentence. The full moon nearly always appears coppery red during a total lunar eclipse. That’s because the dispersed light from all the Earth’s sunrises and sunsets falls on the face of the moon at mid-eclipse. Thus the termblood moon can be and probably is applied to any and all total lunar eclipses. It’s only in years where volcanic activity is pronounced that the moon’s face during a total lunar eclipse might appear more brownish or gray in color. Usually, the moon looks red. We astronomy writers often say it looks blood red. Why? Because it sounds dramatic, and a lunar eclipse is a dramatic natural event. Read more here: Why does the moon look red during a total lunar eclipse?
What’s more, in folklore, all the full moons have names. The names typically coincide with months of the year, or seasons. One of the most famous moon names is the Hunter’s Moon. It is the the full moon immediately following the Harvest Moon, which is the full moon occurring most closely to the autumnal equinox.
The Hunter’s Moon, in skylore, is also sometimes called the Blood Moon. Why? Probably because it’s a characteristic of these autumn full moons that they appear nearly full – and rise soon after sunset – for several evenings in a row. Many people see them when they are low in the sky, shortly after they’ve risen, at which time there’s more atmosphere between you and the moon than when the moon is overhead. When you see the moon low in the sky, the extra air between you and the moon makes the moon look reddish. Voila. Blood moon.
The second total lunar eclipse of the coming lunar tetrad will take place on October 8, the same night as the Hunter’s Moon. So there will be two reasons to use the term Blood Moon that night.
Dates for the Northern Hemisphere’s Harvest and Hunter’s Moons in 2014 and 2015:
Harvest Moon: September 9
Autumn Equinox: September 23
Hunter’s (Blood) Moon: October 8
Autumn Equinox: September 23
Harvest Moon: September 28
Hunter’s (Blood) Moon: October 27
Bottom line: The term Blood Moon in Biblical prophecy appears to have been popularized by two Christian pastors, Mark Blitz and John Hagee. They use the term Blood Moon to apply to the full moons of the upcoming tetrad – four successive total lunar eclipses, with no partial lunar eclipses in between, each of which is separated from the other by six lunar months (six full moons) – beginning on the night of April 14-15, 2014.
Follow their links below to learn more about Blood Moons: