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What Is a Blood Moon?

A total lunar eclipse is sometimes called a Blood Moon, owing to the reddish tinge of the eclipsed Full Moon. The term is also used to describe 4 total lunar eclipses that occur in a row.

Total lunar eclipse.

A total lunar eclipse can be a Blood Moon.

Blood Moon is sometimes used to describe 4 total lunar eclipses in a row.


Why Blood Moons Are Red

While Blood Moon is not a scientific term, it is used colloquially to refer to a total lunar eclipse, because a fully eclipsed Moon often takes on a reddish color. So why does the Moon turn red?

A total lunar eclipse happens when the Moon travels through the Earth's umbra, the dark central portion of its shadow, and the Earth blocks all direct sunlight from falling onto the Moon's surface. However, the Moon does not turn completely dark during a total eclipse as part of the sunlight still reaches the lunar surface indirectly, via the Earth's atmosphere.

As the Sun's rays pass through the atmosphere, some of their colors are filtered out by a phenomenon called Rayleigh scattering, which 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 during the eclipse, different parts of the light spectrum are filtered out, so the Moon may also look yellow, orange, or brown during a total lunar eclipse.

Lunar Tetrad

The term Blood Moon is also sometimes used to refer to four total lunar eclipses that happen in the space of two years, a phenomenon astronomers call a lunar tetrad. The eclipses in a tetrad occur six months apart with at least six Full Moons between them.

Usually, only about one in three lunar eclipses are total, and about four to five total eclipses can be seen from any single location on Earth in a decade. This means that lunar tetrads are rare occurrences, leading some to attach special, even religious, significance to these events.

Blood Moons & the 2014–2015 Lunar Tetrad

Dates of the Total Lunar Eclipse Tetrad 2014 - 2015
2014–2015 lunar tetrad.
2014–2015 lunar tetrad.

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. Some even called the eclipses Blood Moons after a statement in the Book of Joel in the Hebrew Bible, that referred to the Sun turning dark and the Moon turning red before the second coming of Jesus.

Christian pastors Mark Blitz and John Hagee are thought to have been instrumental in popularizing the idea of the prophetic nature of the 2014–2015 Blood Moons, which supposedly had special significance because they coincided with important Jewish festivals. The April 15, 2014 and April 4, 2015 Total Lunar Eclipses occurred at the same time as Passover, while the October 8, 2014 and September 28, 2015 eclipses occurred during the Feast of Tabernacle.

The 2014–2015 lunar tetrad or Blood Moons were significant for an additional reason—all 4 total lunar eclipses were visible from most of the United States. The September 28, 2015 eclipse was the last total lunar eclipse visible from mainland USA until January 31, 2018.

Another Prophecy That Never Came True

Reports of impending doom due to the Blood Moon prophecy were clearly exaggerated, especially since 8 tetrads since 1 C.E. have coincided with Jewish holidays without the world going under. In fact, prior to the last eclipse of the 2014–2015 tetrad, many religious organizations debunked the doomsday claims and reassured their followers that the world wasn't going to end anytime soon.

How Often do Lunar Tetrads Happen?

It depends on the century you look at. Italian astronomer Giovanni Schiaparelli calculated that the occurrence of lunar tetrads varies over centuries. Some 300-year intervals have several lunar tetrads, while other 300-year intervals do not have any. For example, the years between 1582 and 1908 did not have any tetrads, whereas the next 250 years—from 1909 to 2156—will have 17 tetrads.

When's the Next Blood Moon?

According to NASA, the current century—2001 to 2100—will have 8 tetrads. The first tetrad of the 21st century took place in 2003, the second was in 2014–2015, and the next will be in 2032–2033, with the following eclipses:

Upcoming 5 Total Lunar Eclipses

More details about upcoming Eclipses

Topics: Astronomy, Eclipses, Moon

Next Total Lunar Eclipse


Total Lunar Eclipse

Jan 31, 2018 at 10:51:13 UTCSee more


Eclipse Lookup

Lunar Eclipses

  1. When Is the Next Lunar Eclipse?
  2. Total Lunar Eclipse
  3. Why Does the Moon Turn Red?
  4. Partial Lunar Eclipse
  5. Penumbral Lunar Eclipse
  6. Can I See a Lunar Eclipse?
  7. Blood Moon - Total Lunar Eclipse
  8. Magnitude of Eclipses


Eclipse Shadows

  1. Umbra
  2. Penumbra
  3. Antumbra

Why Are There 3 Shadows?

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