The totally eclipsed moon on April 15, 2014 from Duluth, Minn. This was the first in the series of four eclipses called a tetrad. Some refer to this lunar eclipse as a “Blood Moon” because it coincides with the Jewish Passover. Credit: Bob King
Doing anything this weekend? The third in a series of four total lunar eclipses happens early Saturday morning across North and South America, Hawaii, Asia and Australia. If you live in the eastern half of the U.S. and Canada however, this will be a partial eclipse with the moon setting before totality.
Bacon could be an option after watching Saturday’s dawn eclipse. Credit: Bob King
There’s nothing like the bacon-colored eclipsed me to get you thinking about breakfast. Weather permitting, my friends and I hope to watch the event together and then make a beeline for breakfast at sunrise. The timing couldn’t be better.
When four total lunar eclipses occur in a row with no partials in between, it’s called a tetrad. We’re three-quarters through the current tetrad with the final of the four slated for September 28 this year. Tetrads can be relatively common, as they will be this century with the maximum of eight, or rare, as they were during the 300 year period between 1600 and 1900, when there were exactly zero.
When Sun, Earth and full moon all lie in a straight line, the moon moves directly behind Earth and into its shadow, giving us a lunar eclipse. Because of the moon’s tilted orbit and the small size of Earth’s shadow at the moon’s distance (just 1.4°) the moon misses the shadow, but several times a year, the alignment is exact and we get an eclipse.
Lunar eclipses happen when the Sun, Earth and full moon all lie in a straight line. The moon moves into the two-part shadow cast by the Earth and we see an eclipse. Because the moon’s orbit is tilted about 5°, it usually misses the shadow during most full moons or only passes through the outer part for a partial eclipse.
Earth’s shadow is composed of two nested components – the inner umbra, where the Earth completely blocks the Sun from view, and an outer penumbra, where the planet only partially blocks the sun. Because the penumbra is a mix of shadow and sunlight, it’s nowhere near as dark as the umbra. You can see the slight penumbral shading beginning about a half hour before partial eclipse and up to a half hour after it ends.
Animation showing the moon’s path through Earth’s shadow on April 4th. Credit: Tom Ruen
Saturday’s eclipse is unusual because the moon only barely makes it inside the umbra with totality lasting just under 5 minutes. Partial phases, which begin when the moon first touches the umbra and end when it departs, are far more generous, lasting better than 3 1/2 hours.
If you live in the eastern U.S. along the coast, the moon will only be 10-20% covered in Earth’s shadow near the time it sets in morning twilight. That fraction increases to 50-75% or more for the Midwest. Totality occurs in morning twilight shortly before moonset in the mountain states, while lucky West Coasters will see the fully eclipsed moon in dark sky. Hands down, Hawaii’s the best place to see it for obvious reasons but also because you’ll be able to watch the entire event in a dark sky.
Map showing eclipse visibility across the western hemisphere. West of a line running through western Minnesota, Iowa, Missouri, Arkansas and Louisiana, skywatchers will see a total eclipse before moonset. Inset map shows worldwide visibility. Credit: Larry Koehn / shadowandsubstance.com. Inset: Fred Espenak
To see the eclipse at its best, whether that be partial or total, find a spot with a clear view to the southwest. For much of the U.S., the moon will be dropping down toward the southwest horizon during morning twilight. The moon begins the night before as full, but when you get up before dawn on Saturday, you’ll see a bite taken out of it. That bite grows bigger as the moon drops closer to the horizon.
For much of the Midwest, the moon will appear half to two-thirds eclipsed low in the southwestern sky in a bright dawn sky. This is the view from Chicago at 6:15 a.m. with the moon just 3° high. Created with Stellarium
Given its low altitude and the light of dawn, this will be a perfect opportunity to photograph the eclipse against a landscape or skyline. Even a mobile phone will be able to handle the challenge — go for it!
One fun thing to watch for during the event, especially where totality is visible in a dark sky, is the return of darkness and a starry sky. The color of the moon is also a variable. Sometimes it’s bright copper orange, others time smoky brown depending on the amount of particulates like salt, water and volcanic dust suspended in the atmosphere. This should be a bright totality if only because the moon passes just within the umbra’s edge.
Phases of a lunar eclipse leading to totality (right). Credit: Jim Schaff
You’d think the moon would disappear when it slid into Earth’s shadow. Hardly. If we had no atmosphere it would, but that thin layer of air filters the sunlight grazing the planet’s edge and colors it red and orange just like a sunset or sunrise. The atmosphere also acts like a lens and bends or refracts the red light directly into the shadow, coloring the moon.
This diagram shows how the moon moves through Earth’s shadow during the eclipse. Times are Central Daylight (Midwest, central Canada and Mid-South). Because the Sun rises around 6:30-45 a.m., totality won’t be visible in the central part of the country. Credit: Fred Espenak
I like to imagine standing on the lunar surface, bathed in red during the eclipse, looking back toward Earth eclipsing the Sun. Seen from this perspective, Earth wears a marvelous collar of sunrise-sunset light.
Seen from the moon, a total lunar eclipse becomes a total solar eclipse with the Earth eclipsing the Sun. Notice the Earth’s red rim. Created with Stellarium
For more cool stuff to see during this eclipse, click HERE. The diagram above shows the CDT or Central Daylight viewing times. Click below for others:
* Eastern Daylight time diagram
* Mountain Daylight time diagram
* Pacific Daylight time diagram
* Alaska Daylight time diagram
* Hawaii Daylight time diagram
For skywatchers in the eastern half of the country to make the most of the eclipse, it helps to know the time the sun rises for your town. Plan to be out at least an hour and a half before that to catch the show.
For observers either not in the eclipse zone or unfortunately clouded out, you can watch it online at SLOOH and the Virtual Telescope Project. If you do take any pictures of the shadow-dipped moon, please send them to me at firstname.lastname@example.org and I’ll put up a gallery later Saturday morning … after I finish breakfast. Good luck and enjoy!