4 Blood Moons T-Shirt

The National Aeronautics and Space Administration ( NASA ) defines the occurrence of 4 consecutive total lunar eclipses as a Tetrad. In the years 2014 - 2015 a rare Tetrad sequence will occur on the Jewish Holidays of Passover and the Feast of Tabernacles. In addition to the Tetrad occurrence, 2 total solar eclipses will complement the 4 lunar eclipses on the Jewish New Year and the Feast of Trumpets. Eclipses may occur when the Earth and the Moon are aligned with the Sun, and the shadow of one body cast by the Sun falls on the other. So at new moon (or rather Dark Moon), when the Moon is in conjunction with the Sun, the Moon may pass in front of the Sun as seen from a narrow region on the surface of the Earth and cause a solar eclipse. At full moon, when the Moon is in opposition to the Sun, the Moon may pass through the shadow of the Earth, and a lunar eclipse is visible from the night half of the Earth. Tetradia ; Sometimes 4 total lunar eclipses occur in a row with intervals of 6 lunations (semester), and this is called a tetrad. Giovanni Schiaparelli noticed that there are eras when such tetrads occur comparatively frequently, interrupted by eras when they are rare. This variation takes about 6 centuries. Antonie Pannekoek (1951) explained this phenomenon and found a period of 591 years. Van den Bergh (1954) from Theodor von Oppolzer's Canon der Finsternisse found a period of 586 years. This happens to be an eclipse cycle; see Meeus [I] (1997). Recently Tudor Hughes explained the variation from secular changes in the eccentricity of the Earth's orbit: the period for occurrence of tetrads is variable and currently is about 565 years; see Meeus III (2004) for a detailed discussion.