Those of you who were able to witness the "Blood Moon" on Oct. 8 know what an incredible sight it was to see the total lunar eclipse of the moon and the rising sun simultaneously.

This effect, called a "selenelion," cannot happen according to celestial geometry, because the moon and the sun are exactly 180 degrees apart during a lunar eclipse (a perfect alignment like this is called a "syzygy"). However, thanks to the trick of atmospheric refraction caused by the earth's atmosphere, we were able to observe the images of both the sun and moon, lifted above the horizon.

What is most unique about the 2014-2015 tetrad is that it is visible to all or most parts of the U.S. The Oct. 8 lunar eclipse was visible to observers in North America, western South America, parts of East Asia, Australia and other parts of the Pacific (weather permitting). This blood moon is the second of the "tetrad"--the next will appear April 4, 2015, and the last will appear on September 28, 2015.

A one-minute time lapse video of NASA TV footage posted on CNN can be seen here, and other remarkable photos of views of the blood moon around the world can be seen in the the tweets below.