An unusual lunar eclipse that will cause the moon to glow red is expected to occur on April 15.

A total lunar eclipse, also called a "Full Pink Moon," "Blood Red Moon" or "April's Full Moon" will occur on April 15 at 3:42 a.m. GMT. The eclipse will be visible in North and South America, New Zealand, Australia and other parts of the Pacific area. The eclipse is expected to last around 77 minutes. 

The total eclipse will last from 3:07 a.m. until 4:25 a.m. EDT, and partial phases of the eclipse will be able to be viewed for a few hours before and after the total eclipse. 

The moon will appear to have a red shade because the Earth will be positioned directly between the moon and the sun, and the sun's rays are blocked from reaching the moon directly, which means light is reflected off the Earth. As a result, the reflected rays of light will cause the moon to glow with an orange-red color. 

Two factors affect an eclipse's brightness and color: the depth of the moon into the umbra, and the Earth's atmosphere.

The umbra's center is much darker than its outer edge, so the depth of the moon into the umbra will affect the moon's color and brightness. Also, if the atmosphere is very clear, the eclipse will be bright, whereas if it's cloudy (or polluted with volcanic ash,) the eclipse will be dark red or nearly black. 

After the April 15 eclipse, another lunar eclipse will occur two weeks later. 

On April 29, an annular, or "ring of fire" eclipse will be visible from a small region in Antarctica around 2:04 a.m. EDT. 

The April 15 lunar eclipse will be the first of four that are expected to occur within the next two years. The four eclipses, which are called a tetrad, is very uncommon. 

"During the 21st century, there are 9 sets of tetrads, so I would describe tetrads as a frequent occurrence in the current pattern of lunar eclipses," explained Fred Espenak, who studies lunar eclipse patterns at NASA. "But this has not always been the case. During the three hundred year interval from 1600 to 1900, for instance, there were no tetrads at all.

"The most unique thing about the 2014-2015 tetrad is that all of (eclipses) are visible for all or parts of the USA," he added.

The three other eclipses that will occur in the tetrad will be on Oct. 8, 2014; April 4, 2015; and Sept. 28, 2015. All eclipses will be visible from at least a part of the United States.