by: Alli Gay ’15
A blood moon as seen from Earth.
(Photo credit: “Blog Archives.” ॐ Heartbliss ॐ. N.p., n.d. Web. 08 Jan. 2015.)
What Causes a Blood Moon?
Because the moon’s orbit is slightly tilted, most of the time the moon passes above or below the Earth’s shadow and no eclipse occurs. Sometimes, it passes only through the penumbra and produces what is called a penumbral eclipse, a moon so lightly shaded that the casual observer might not even notice a difference. Sometimes the moon only dips slightly into the central shadow and it produces a partial lunar eclipse. The rarest of all lunar eclipses are those in which the moon passes through the darkest part of the shadow, a true total lunar eclipse.
A Blood Moon can occur during a total lunar eclipse. A total lunar eclipse occurs when the moon passes through the Earth’s shadow. The Earth’s shadow consists of two parts:
– a dark inner core called the “umbra”
-a lighter outer part called the “penumbra”
Rather than being truly dark, the inner shadow is usually tinted orange or red by light passing through the ring of atmosphere surrounding the Earth.
This diagram depicts a total lunar eclipse.
(Photo source: “Lunar Eclipse on Wednesday 15 June.” Enjoy Space :. N.p., n.d. Web. 06 Jan. 2015.)
Depending on the atmospheric conditions of Earth in the band of atmosphere through which the sun’s light passes, the umbra may take on a range of colors from a light coppery-red to almost total black. During others, clouds may block the light, causing a dark eclipse. On rare occasions, the light reaching the moon is a blood-red.
In conclusion, a blood moon is the rarest color of the rarest form of an eclipse.
Four Blood Moons: The Lunar Eclipse Tetrad
Every once in a while, four blood moons occur over a year-long period. This is called a tetrad. Two nights in 2014, April 15th and October 8th, a deep red full moon hung in the sky. There will be two blood moons in 2015 as well on April 4th and September 28th. Mark down the dates on your calendars if you want to witness this rare and beautiful event.
A blood moon as seen from space.
(Photo credit: “Lunar Eclipse on Wednesday 15 June.” Enjoy Space :. N.p., n.d. Web. 06 Jan. 2015.)