Posted on by Bob King

Don’t Blink! April 4th Lunar Eclipse Shortest of the Century

The phases of a total lunar eclipse. Credit: Keith Burns / NASA

Get ready for one awesome total lunar eclipse early Saturday morning April 4th. For the third time in less than a year, the Moon dips into Earth’s shadow, its dazzling white globe turning sunset red right before your eyes.  All eclipses are not-to-miss events, but Saturday’s totality will be the shortest in a century. Brief but beautiful – just like life. Read on to find out how to make the most of it.

Four total lunars in succession is called a tetrad. During the 21st century there are nine sets of tetrads. Credit: NASA
Four total lunar eclipses in succession with no partials in between is called a tetrad. The April 4th eclipse is part of a tetrad that started last April and will wrap up on September 28. During the 21st century there will be eight sets of tetrads. Credit: NASA

Lunar eclipses don’t usually happen in any particular order. A partial eclipse is followed by a total is followed by a penumbral and so on. Instead, we’re in the middle of a tetrad, four total eclipses in a row with no partials in between. The final one happens on September 28.  Even more remarkable, part or all of them are visible from the U.S. Tetrads will be fairly common in the 21st century with eight in all. We’re lucky — between 1600 and 1900 there were none! For an excellent primer on the topic check out fellow Universe Today writer David Dickinson’s “The Science Behind the Blood Moon Tetrad“.

The Moon moves out of total eclipse and into partial phases during the second of the four tetrad eclipses on October 8, 2015. Credit: Bob King
The partially eclipsed Moon on October 8, 2015.  For skywatchers across the eastern half of North America, this is about how the Moon will appear shortly before it sets. Those living further west will see totality. Credit: Bob King

Lots of people have taken to calling the tetrad eclipses Blood Moons, referring to the coppery color of lunar disk when steeped in Earth’s shadow and the timing of both April events on the Jewish Passover. Me? I prefer Bacon-and-Eggs Moon. For many of us, the eclipse runs right up till sunrise with the Moon setting in bright twilight around 6:30 a.m. What better time to enjoy a celebratory breakfast with friends after packing away your gear?

Map showing where the April 4 lunar eclipse will be penumbral, partial and total. Inset shows a world map. Credit: Larry Koehn / shadowandsubstance.com
Map showing where the April 4 lunar eclipse will be penumbral, partial and total. World map shown in inset. Credit: Larry Koehn / shadowandsubstance.com Inset: Fred Espenak

But seriously, Saturday morning’s eclipse will prove challenging for some. While observers in far western North America, Hawaii, Japan, New Zealand and Australia will witness the entire event, those in the mountain states will see the Moon set while still in totality. Meanwhile, skywatchers in the Midwest and points East will see only the partial phases in a brightening dawn sky. Here are the key times of eclipse events by time zone:

A total lunar eclipse occurs only during Full Moons when the Sun, Earth and Moon form a straight line. The Moon slips directly behind Earth into its shadow. The outer part of the shadow or penumbra is a mix of sunlight and shadow. The inner cone, called the umbra, the Sun is completely blocked from view. However, light refracted by Earth's atmosphere is bent into the umbra where it colors the eclipsed Moon red.
A total lunar eclipse occurs only during full moon phase when the Sun, Earth and Moon lie in a straight line. The Moon slips directly behind Earth into its shadow. The outer part of the shadow or penumbra is a mix of sunlight and shadow and only partially dark. From  the inner shadow, called the umbra, the Sun is completely blocked from view. A small amount of sunlight refracted or bent by Earth’s atmosphere into the umbra, spills into the shadow, coloring the eclipsed Moon red.

Eclipse Events                                     EDT              CDT              MDT             PDT

Penumbra eclipse begins 5:01 a.m. 4:01 a.m. 3:01 a.m. 2:01 a.m.
Partial eclipse begins 6:16 a.m. 5:16 a.m. 4:16 a.m. 3:16 a.m.
Total eclipse begins ——– ——– 5:58 a.m. 4:58 a.m.
Greatest eclipse ——– ——– 6:00 a.m. 5:00 a.m.
Total eclipse ends ——– ——– 6:03 a.m. 5:03 a.m.
Partial eclipse ends ——— ——– ——– 6:45 a.m.
Penumbra eclipse ends ——— ——— ——– ——–

* During the penumbral phase, shading won’t be obvious until ~30 minutes before partial eclipse.

Partial eclipse, when the Moon first enters Earth's dark, inner shadow called the umbra, begins at 5:16 a.m. CDT near the start of morning twilight. Totality begins at 6:58 a.m. with the Moon already set for the eastern half of the country. Credit: Fred Espenak
Partial eclipse, when the Moon first enters Earth’s dark umbral shadow, begins at 5:16 a.m. CDT near the start of morning twilight. Totality begins at 6:58 a.m. with the Moon already set for the eastern half of the country. Credit: Fred Espenak

This eclipse will also be the shortest total eclipse of the 21st century; our satellite spends just 4 minutes and 43 seconds inside Earth’s umbra or shadow core. That’s only as long as a typical solar eclipse totality. Ah, the irony.

Better have your camera ready or you’ll miss it. The maps below show the maximum amount of the Moon visible shortly before setting from two eastern U.S. cities and the height of the totally eclipsed Moon from two western locations. Click each panel for more details about local circumstances.

The Earth's shadow will take only a small bite out of the Moon before sunrise (6:47 a.m.) as seen from Washington D.C. Source: Stellarium
The Earth’s shadow will take only a small bite out of the Moon before sunrise (6:47 a.m.) as seen from Washington D.C. From all mainland U.S. locations Virgo’s brightest star Spica will appear about 10° to the left of the Moon. Source: Stellarium
Here's the view from Chicago where sunrise occurs at 6:27 a.m. Source: Stellarium
Here’s the view from Chicago where sunrise occurs at 6:27 a.m.  Source: Stellarium
Totality will be visible From Denver, Colorado with the Moon low in the western sky. Source: Stellarium
Totality will be visible From Denver, Colorado with the Moon low in the western sky in morning twilight. Sunrise is 6:42 a.m. Source: Stellarium
Seattle and the West Coast get a great view of totality in a dark sky. The final partial phases will also be visible. Sunrise there is 6:40 a.m. Source: Stellarium
Seattle and the West Coast get a great view of totality in a dark sky. The final partial phases will also be visible. Sunrise there is 6:40 a.m. Source: Stellarium

Now that you know times and shadow coverage, let’s talk about the fun part — what to look for as the event unfolds. You’ll need to find a location in advance with a good view to the southwest as most of the action happens in that direction. Once that detail’s taken care of and assuming clear weather, you can kick back in a folding chair or with your back propped against a hillside and enjoy.

During the early partial phases you may not see the shadowed portion of the Moon with the naked eye. Binoculars and telescopes will show it plainly. But once the Moon's about 50% covered, the reddish-orange tint of the shadowed half becomes obvious. Credit: Jim Schaff
During the early partial phases you may not see the shadowed portion of the Moon with the naked eye. Binoculars and telescopes will show it plainly. But once the Moon is about 50% covered, the reddish-orange tint of the shadowed half becomes obvious. During total eclipse (right), the color is intense.  Credit: Jim Schaff

The entire eclipse can be enjoyed without any optical aid, though I recommend a look through binoculars now and then. The eclipsed Moon appears distinctly three-dimensional with only the slightest magnification, hanging there like an ornament among the stars. The Earth’s shadow appears to advance over the Moon, but the opposite is true; the Moon’s eastward orbital motion carries it deeper and deeper into the umbra.

Nibble by nibble the sunlit Moon falls into shadow. By the time it’s been reduced to half, the shaded portion looks distinctly red even to the naked eye. Notice that the shadow is curved. We live on a spherical planet and spheres cast circular shadows. Seeing the globe of Earth projected against the Moon makes the roundness of our home planet palpable.

Artist view of Earth totally eclipsing the sun as viewed from the moon. Low angled sunlight filtered by our atmosphere is reddened in exactly the same way a setting sun is reddened. That red light bathes the moon’s surface which reflects a bit of it back toward Earth, giving us a red moon during totality.
A simulated view looking back at Earth from the Moon during a total lunar eclipse on Earth. Sunlight grazing Earth’s circumference gets filtered by our atmosphere in exactly the same way the setting or rising Sun looks red. All the cooler colors have been scattered away by air and Red light, bent into the umbra by atmospheric refraction, bathes the lunar surface in red. As you might have guessed, when we see a total lunar eclipse on Earth, lunar inhabitants see a total eclipse of the Sun by Earth. Source: Stellarium

When totality arrives, the entire lunar globe throbs with orange, copper or rusty red. These sumptuous hues originate from sunlight filtered and bent by Earth’s atmosphere into the umbral shadow. Atmospheric particles have removed all the cooler colors, leaving the reds and oranges from a billion sunrises and sunsets occurring around the planet’s circumference. Imagine for a moment standing on the Moon looking back. Above your head would hang the black disk of Earth, nearly four times the size of the Moon in our sky, ringed by a narrow corona of fiery light.

Color varies from one eclipse to the next depending on the amount of water, dust and volcanic ash suspended in Earth’s atmosphere. The December 30, 1982 eclipse was one of the darkest in decades due to a tremendous amount of volcanic dust from the eruption of the Mexican volcano El Chichon earlier that year.

The more particles and haze, the greater the light absorption and darker the Moon. That said, this eclipse should be fairly bright because the Moon does not tread deeply into Earth’s shadow. It’s in for a quick dip of totality and then resumes partial phases.

The Moon's color can vary from yellow-orange to dark, smoky brown during totality depending on the state of the atmosphere. You can also see lots of stars in the sky right up to the Moon's edge when it's in Earth's shadow. This photo from last April's eclipse. Credit: Bob King
The Moon’s color can vary from yellow-orange to dark, smoky brown during totality depending on the state of the atmosphere. You can also see lots of stars in the sky right up to the Moon’s edge when it’s in Earth’s shadow. This photo from last April’s eclipse. Spica is below the Moon and Mars to the right. Credit: Bob King

It’s northern edge, located close to the outer fringe of Earth’s umbra, should appear considerably brighter than the southern, which is closer to the center or darkest part of the umbra.

Earth's shadow exposed! During a lunar eclipse that occurs at dusk or dawn (like the April 4th one and this one last October) we have the rare opportunity to see Earth's shadow on the distant Moon at the same time it's visible as a dark purple band cast on the upper atmosphere as seen here on October 8, 2015. Credit: Bob King
Earth’s shadow exposed! When a lunar eclipse occurs at dusk or dawn we have the rare opportunity to see Earth’s shadow on the distant Moon at the same time it’s visible as a dark purple band cast on the upper atmosphere as seen here on October 8, 2015. Credit: Bob King

Besides the pleasure of seeing the Moon change color, watch for the sky to darken as totality approaches. Eclipses begin with overwhelming moonlight and washed out, star-poor skies. As the Moon goes into hiding, stars return in a breathtaking way over a strangely eerie landscape. Don’t forget to turn around and admire the glorious summer Milky Way rising in the eastern sky.

Lunar eclipses remind us we live in a Solar System made of these beautiful, moving parts that never fail to inspire awe when we look up to notice.

In case you can’t watch the eclipse from your home due to weather or circumstance, our friends at the Virtual Telescope Project  and SLOOH will stream it online.