Wednesday's blood moon is bigger than April's and the second in a series of four

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People in the Americas have been treated to a rare "blood moon" lunar eclipse. Jonathan Amos explains the science behind the colour change.

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The Denver Post reported on Oct. 4 that a “blood moon” or total lunar eclipse will be visible in the night skies on Wednesday. This total eclipse is the second in a series of four (tetrad) blood moons scheduled to appear through 2015. The Wednesday total lunar eclipse will appear bigger than the one from April and those living in the western states will have access to some of the most impressive views.

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You’ll have to get up early to view the sight, though not quite as early (or late) as the April eclipse required. The event begins about 2:17 a.m. MSTwith totality predicted to last from 4:27 a.m. to 5:22 a.m. The total length of the eclipse will last till right after sunrise.

Blood moons are named such because the moon looks red or reddish orange when it has completely become eclipsed. The cause for this coloring is the way sunlight refracts off of the Earth’s atmosphere as the Earth’s shadow completely covers the moon. The moon will appear so big to the eye, (almost as big as a supermoon!) because of its placement in space at the time of the eclipse. The moon will be at the closest point to the Earth in its orbit and appear a little more than 5 percent larger than April’s total lunar eclipse.

The tetrad of blood moons is a rarity that will only occur 8 times total in the 21st century with the first of them having appeared in 2003 and the last of them to appear in 2091. According to NASA, the appearance of tetrads (a succession of total lunar eclipses without partial or penumbral eclipses occurring during that succession) are variable over time. None appeared between the years 1582 and 1908 but 17 happened or will happen from 1909 to 2156. At some point, tetrads will not occur, as the Earth’s orbit changes in eccentricity.

The Oct. 8 blood moon appears just six months after the last one. Succeeding blood moons will appear in approximately six month intervals with the next to appear on April 4, 2015 and September 28, 2015.

*originally published on the now defunct Examiner.com