The term "blood moon" is not used in official astronomy. However, they denote a lunar eclipse that occurs on a full moon. The shadow of the Earth floats to the Moon, it completely closes and turns into a blood-red hue due to a certain refraction in the atmosphere of the sun's rays.
When the moon is called "bloody"
"Blood moons" are not uncommon, they occur once every five to six months. However, this phenomenon can not always be observed, at this moment the Moon may be behind the horizon. An eclipse occurs when the Earth is between the Sun and the Moon, and the Moon enters the shadow cast by the Earth. Such an eclipse is considered complete, the disk of the moon is always in sight, it darkens and changes color. During an eclipse, the sun's rays reach the Earth's satellite only from the red part of the spectrum, as a result of which the Moon becomes crimson.
"Blood moon" in the old days terrified people. Such phenomena were attributed to ominous influence on future events. It was believed that the moon was bleeding at this time, which predicted great misfortunes. The first such eclipse was recorded in the ancient Chinese annals in 1136 BC. The last time in Russia the "bloody moon" was observed on April 15, 2014. This phenomenon is included in the so-called "tetrad" - four total lunar eclipses, passing one after the other within two years. Dates for the following three total lunar eclipses: October 8, 2014, April 4, 2015, September 28, 2015.
Tetrads, their role in predictions
Tetrads are rare. 142 tetrads have been observed over the past 5000 years, the last of which occurred in 2003-2004. Moreover, in the period from 1582 to 1908 there was not a single tetrad, and in the period from 1909 to 2156 there will be 17. According to the Canadian Astronomical Society, the "bloody moon" can be observed in 2032-2033 and 2043-2044. In April 2014, in addition to the first red moon of the tetrad, the Sun, Earth and Mars lined up in one line. In the predictions of the biblical prophet Joel it is written that the apocalypse will come "when the sun turns into darkness and the moon turns into blood." The same thing is repeated in Revelation (chapter six) and in Acts (2:20), so Christians seriously think about the end of the world.
There are several notebooks left in history, which became bloody not only because of the color. In 162-163 AD, they preceded the persecution of Christians under Marcus Aurelius. The next tetrad took place in 1493-1494, and before that, in 1492, an edict of Ferdinand and Isabella was announced in Spain about the expulsion of Jews from the country. Blood moons in 1949-1950 were observed after the end of the Israeli War of Independence. It is also noteworthy that all 4 eclipses of 2014-2015 fall on Jewish holidays - twice on the Feast of Tabernacles (Sukkot) and twice on the Jewish Passover. Among the Muslims, eclipses are also indicated among the signs of the approaching Doomsday.