Tuesday’s Total Lunar Eclipse Ushers in Series of Four

In the early morning hours of Tuesday, April 15, a total lunar eclipse will be visible across North America, turning the moon blood red or orange as the moon passes through Earth’s shadow.

The colorful eclipse ushers in an unusual series of astronomical events, said Dr. Mary Urquhart, associate professor and head of the Department of Science and Mathematics Education at The University of Texas at Dallas.

“This is the first of four, consecutive total lunar eclipses occurring at approximately six-month intervals, an occurrence known as a ‘tetrad of lunar eclipses,’” said Urquhart, who also is a planetary scientist.

“Also, all four eclipses will be visible from North America, which makes this tetrad special for sky watchers in the United States.”

Lunar eclipses occur roughly twice a year, when the sun, Earth and moon are lined up in such a way that the full moon crosses Earth’s shadow. (Parents: Download a PDF of an eclipse model that you and your children can build.)  But only a fraction are total eclipses — when the entire moon is covered by Earth’s shadow. During a partial eclipse, for example, only a portion of the moon is darkened, and during a penumbral eclipse, the moon barely skirts the edge of Earth’s shadow. Typically, these types of eclipses occur in no particular order.

“It’s not often that we have the opportunity to witness four total eclipses in a row,” Urquhart said. “If you don’t mind staying up a little late, this is a great science activity for students and families to enjoy for free. Weather permitting, of course.”

According to NASA, there will be several tetrads this century; but, between the years 1600 and 1900, there were none. After Tuesday, the other three total lunar eclipses in the current tetrad will occur on Oct. 8; April 4, 2015; and Sept. 28, 2015.

As seen from the Dallas-Fort Worth area, the moon will begin to enter the Earth’s outer shadow, called the penumbra, at about 1 a.m. CDT the morning of April 15. By about 2 a.m., the moon will be completely within the core of Earth’s shadow, and the moon will appear red. This phase, called “totality,” will continue until about 3:25 a.m., when the moon begins to emerge from the shadow and return to its normal color.

Viewers who want to catch a glimpse of the lunar eclipse won’t need any special filters to protect their eyes or their cameras.

“Unlike solar eclipses, lunar eclipses are perfectly safe to look at directly,” Urquhart said. 

So, why does the moon turn red?

“That red color is no more ominous than a sunset,” Urquhart said.

If you were standing on the moon during a lunar eclipse, and looking back at Earth, our planet would block out the sun’s light, except for a thin ring around the circumference of Earth. That ring is our planet’s atmosphere.

“From the moon, we’d be seeing light filtered and bent through Earth’s atmosphere, which is essentially the light of all the sunsets and sunrises occurring at that time,” Urquhart said. “We normally don’t see the Earth-reddened light on the full moon simply because it’s outshone by the sun’s light.”

The Texas Astronomical Society will host a free lunar eclipse watch from 12:30 a.m. to 4:30 a.m. April 15 at Brookhaven College in Farmers Branch.