It’s been too long. The moon last slipped into Earth’s shadow for North America in Dec. 2011. Next Monday night’s eclipse will end the current dry spell and make for a thrilling night out.
This eclipse is the first of four total lunar eclipses spaced about six months apart that will be visible across most of the Americas. The others occur on Oct. 8 this year, April 4, 2015 and Sept. 27, 2015. This particular sequence of four total lunar eclipses with no partials in between is called a ‘tetrad’. While we all hope for clear skies, if the weather’s uncooperative next week, you won’t have to wait long for another eclipse.
Eclipse tetrads explained
Lunar eclipses unfold slowly, lasting up to five hours. Unlike a total solar eclipse, where the sun disappears at most a few minutes, totality during a lunar eclipse can easily last more than an hour, giving you lots of time to enjoy the spectacle.
The only downside will be the late hour. Try to get some shuteye early as most of the eclipse happens after midnight in the wee hours Tuesday morning.
Lunar eclipses occur during full moon when the sun, Earth and moon line up in a neat row, and the moon passes into the shadow cast by our planet. You’d think eclipses would happen every full moon, but they don’t because the moon’s orbit around the Earth is tipped 5 degrees to Earth’s orbit around the sun.
The moon spends most of the time above or below the plane of Earth’s orbit. And since Earth casts a shadow across its orbital plane, a lunar eclipse can only happen if the moon happens to be crossing that plane at the same time it’s full. That’s why eclipses are such a now and again thing.
While total solar eclipses are only visible along a narrow strip of land or ocean, a total lunar can be seen across half the globe wherever the sky is dark and the moon is up.
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.
An eclipse is divided into stages beginning with the moon’s entry into Earth’s lighter penumbral shadow. Most of us won’t notice any shading at all until about a half hour in, when the moon is deep enough inside to reveal a subtle darkening along its eastern edge. The table below lists the times for each stage of the eclipse across the four time zones:
Eclipse Events EDT CDT MDT PDT
|Penumbra visible||1:20 a.m.||12:20 a.m.||11:20 p.m.||10:20 p.m.|
|Partial eclipse begins||1:58 a.m.||12:58 a.m.||11:58 p.m.||10:58 p.m.|
|Total eclipse begins||3:07 a.m.||2:07 a.m.||1:07 a.m.||12:07 a.m.|
|Mid-eclipse||3:46 a.m.||2:46 a.m.||1:46 a.m.||12:46 a.m.|
|Total eclipse ends||4:25 a.m.||3:25 a.m.||2:25 a.m.||1:25 a.m.|
|Partial eclipse ends||5:33 a.m.||4:33 a.m.||3:33 a.m.||2:33 a.m.|
|Penumbra visible||——–||5:10 a.m.||4:10 a.m.||3:10 a.m.|
Partial eclipse begins when the moon treads within the dark umbra. Nibble by nibble the shadow eats away at the lunar disk. When only a sliver of the moon remains in sunlight, you’ll notice the shadowed portion glowing an eerie red or deep copper. To understand why, imagine an astronaut on the moon looking back at Earth during the eclipse.
From her perspective, as the Earth passes in front of the sun, it’s surrounded by a glowing red-orange ring of light. Our atmosphere bends the light from all the sunrises and sunsets around the planet’s circumference into the umbra, coloring the moon red. Earth’s shadow isn’t really black after all but more a deep rusty red. Back on Earth, the moon will hang like a ghostly amber globe near the bright star Spica.
After mid-eclipse, the moon slowly exits the Earth’s shadow and performs the whole show in reverse, transitioning back to partial eclipse and finally exiting the penumbra.
You can take in the eclipse as casually as you like, but are seven cool things you might like to watch for:
#1 – When will you detect the first hint of penumbral shading? Keep an eye on the eastern (left) side of the moon for a “dented” appearance.
#2 – What color and how bright is the totally eclipsed moon? Depending upon the aerosol content of the atmosphere (greatly affected by volcanic eruptions), eclipses range from bright copper to dark brown and even black. Try rating this one on the traditional Danjon scale where “4″ is bright and “0″ is nearly invisible.
#3 – Watch for “the night within the night” phenomenon. If you thought it was dark out at the start of the eclipse, you’ll be amazed at how inky the landscape becomes during totality. As the eclipse progresses, the stars and Milky Way return to view.
#4 – With the entire moon darkened during totality, it will be relatively easy to watch it block or occult any star within its path. Many stars ranging from magnitude +8 and 12 will be occulted when viewed through small to medium telescopes. Click HERE for stars and times.
#5 – Binocular and telescope users should also look for a blue tinge to the encroaching umbral shadow as it slowly envelops the moon caused by light refracted by the upper atmosphere’s ozone layer.
#6 – Variation in the moon’s brightness. The top half will be closer to the center of the umbra and appear darker than the bottom. How obvious will this be?
#7 – Bring home a souvenir with your camera. If you have a telescope, you can hold a cellphone over the eyepiece to get great shots of the bright phases. During total eclipse, longer exposures of 1 to 10 seconds are necessary. For that you’ll need a tripod and a camera that can shoot time exposures. Telephoto lenses will pump up the moon’s size, but even a standard lens can do a great job of recording the sunset-colored moon in a landscape setting. Set your lens to its widest-open setting (f/2.8, 3.5) and expose 10-30 seconds to include the scene.