SUNSET: 
11An unusually brief total eclipse of the Moon will be visible before dawn this Saturday, April 4th, from western North America. The eclipse happens on Saturday evening for Australia and East Asia.
The total eclipse of the Moon on Saturday, April 4th, will be the third in the current "tetrad" of four in a row at half-year intervals.
Sky & Telescope illustration
As was the case last October 8th, this lunar eclipse favors westerners in the U.S. and Canada. And once again many will need to look low in the west as dawn brightens — lower, in fact, than last time.
But in another way this time will be different. This eclipse will be just barely total — in fact, you may get the impression that it never becomes quite total at all. The Moon's north-northeastern limb squeaks so slightly inside the umbra (dark inner portion) of Earth's shadow that it will remain much brighter than the deep red we can expect across the rest of the Moon's face.
So borderline is this eclipse that different authorities give durations of totality ranging from 5 to 12 minutes long — depending on the definition chosen for the exact edge of the umbra, which is actually somewhat fuzzy.
The map, diagram, and timetable here show what to expect at your location and when. Weather permitting, those near the West Coast will see the total phase of the eclipse with the Moon fairly high in a dark sky before dawn even begins. Skywatchers in the Plains states will find dawn brightening and the Moon sinking low in the west around totality. For easterners, the Moon sets (and the Sun rises) during the partial phase before totality begins. New England misses this one altogether.
Meanwhile, as seen from Hawai'i or New Zealand, the eclipse happens deep in the night and high in the sky. For Australia, Japan, China, and Southeast Asia, it comes on Saturday evening local time.
| Total Eclipse of the Moon, April 4, 2015 | ||||||
| Eclipse event | UT |
EDT | CDT | MDT | PDT | HAST |
| Penumbra first visible? | 9:35 | 5:35 a.m. | 4:35 a.m | 3:35 a.m. | 2:35 a.m. | 11:35 p.m. (4/3) |
| Partial eclipse begins | 10:15 | 6:15 a.m. | 5:15 a.m. | 4:15 a.m. | 3:15 a.m. | 12:15 a.m. |
| Total eclipse begins | 11:54 | 7:54 a.m. | 6:54 a.m. | 5:54 a.m. | 4:54 a.m. | 1:54 a.m. |
| Mid-eclipse | 12:00 | — | 7:00 a.m | 6:00 a.m. | 5:00 a.m. | 2:00 a.m. |
| Total eclipse ends | 12:06 | — | 7:06 a.m. | 6:06 a.m. | 5:06 a.m. | 2:06 a.m. |
| Partial eclipse ends | 13:45 | — | — | 7:45 a.m. | 6:45 a.m. | 3:45 a.m. |
| Penumbra last visible? | 14:25 | — | — | — | 7:25 a.m. | 4:25 a.m. |
Where to Watch the Eclipse Online
Can't see the eclipse from where you are? Then check out one of these live webcasts:
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What to Watch for During April 4th's Lunar Eclipse
Sky & Telescope diagram
A total lunar eclipse has five stages, with different things to watch for at each. You only need your eyes to see this celestial drama unfold, though the view is certainly better through binoculars or a small backyard telescope.
The first stage begins when the Moon's leading edge enters the pale outer fringe of Earth's shadow: the penumbra. But the shading is so weak that you won't see anything of the penumbra until the Moon is about halfway across it. Watch for a slight darkening to become apparent on the Moon's celestial southeastern side (likely on the left or lower left as seen in the sky, depending on where you are). The penumbral shading becomes stronger as the Moon moves deeper in.
Johnny Horne
The second stage is the partial eclipse. This begins much more dramatically when the Moon's leading edge enters the umbra, Earth's inner shadow, where no direct sunlight reaches. With a telescope you can watch the edge of the umbra slowly engulf one lunar feature after another. Also note how the entire sky begins to grow darker, as what had been a full Moon gradually disappears.
On April 4th, it'll take a good hour and a half before only a final bright sliver remains outside the umbra. By this time, the rest will already be showing a foreboding reddish glow.
The third stage is total eclipse, beginning when the last rim of Moon slips into the umbra — depending on how the edge of the umbra is defined! The edge is not sharp, since Earth has a semitransparent atmosphere. In a grazing instance like this, so critical is the adopted definition that the U.S. Naval Observatory's Astronomical Almanac (which S&T uses) lists totality as lasting 12.3 minutes, whereas Fred Espenak's Fifty-Year Canon of Lunar Eclipses says 8.6 minutes. The French national almanac lists it as 4.7.
Most of the Moon is sure to glow some shade of intense orange or red. That red light shining onto the Moon is sunlight that has skimmed and bent through Earth's atmosphere: that is, from all the sunrises and sunsets that ring the world at any given moment.
Sky & Telescope illustration
Two factors affect a lunar eclipse's color and brightness. The first is simply how deeply the Moon goes into the umbra as it passes through; the center of the umbra is much darker than its edges. The second factor is the state of Earth's atmosphere along the sunrise-sunset line. If the air there is very clear, the eclipse is bright. But when a major volcanic eruption has recently polluted the stratosphere with thin haze worldwide, a lunar eclipse will be dark red, ashen gray, or occasionally almost black.
In addition, blue light refracted through Earth's clear, ozone-rich upper atmosphere can also add to the scene, especially near the umbra's edge, creating a subtle mix of changing colors. Time-lapse videos may show large "flying shadows" in the umbra, caused by changing cloud-shadowing effects around the sunrise-sunset line as Earth moves and turns.
And then, as the Moon continues eastward along its orbit, events replay in reverse order. The Moon's edge re-emerges into sunlight, ending totality and beginning stage four: a partial eclipse again. When all of the Moon escapes the umbra, only the last, penumbral shading is left for stage five. By about 45 minutes later, nothing unusual remains.
Here's Alex Mellinger's cool time-lapse video of the total lunar eclipse last October, tracked on the reference frame of Earth's shadow:
The Moon's face is rich with geologic wonder. To track down all the details with your telescope, you'll want to have Sky & Telescope's laminated Moon map at your side.
Comments
Larry McNish
March 30, 2015 at 7:46 pm
There are also a couple of minor differences in the timings quoted from the U.S. Naval Observatory's Astronomical Almanac as compared to NASA's Eclipse page for the event, available via: http://eclipse.gsfc.nasa.gov/lunar.html
NASA timings for April 4, 2015:
Total eclipse begins: 11:57:54 UT.
Total eclipse ends: 12:02:37 UT.
Duration of just 4 min 43 sec.
But don't let these small disagreements stop you from going out to observe it!
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Curt Renz
March 31, 2015 at 10:57 pm
Actually, there will be only a partial (nearly total) lunar eclipse during Saturday morning 2015 APR 04. The Earth’s umbra will only cover 99.5% of the Moon’s diameter. Therefore the “tetrad” is spoiled.
Unlike other eclipse sources that assume the Earth’s umbra to be perfectly circular, I take into account the oblate shape of the Earth and the resulting elliptical umbra. I rely on highly accurate positions of the Sun and Moon based on the numerical integration program Solex, and the shape of the Earth from the World Geodetic System.
Belgian eclipse guru Jean Meeus has written eclipse books in association with NASA’s Fred Espenak. They have the upcoming eclipse listed as total. Meeus replied to me in a recent email, “Yes, I know that the lunar eclipse of April 2015 may be partial if the oblateness of the umbra is taken into account.”
Those able to view the eclipse at its maximum may be want to report their opinion of whether the eclipse appears partial or total.
My eclipse preview graphics and data appear at http://www.CurtRenz.com/moon.html
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Fred Espenak
April 1, 2015 at 11:03 am
The USNO defines the diameters of the Moon's umbral and penumbral shadows in a different and older way as compared to the NASA and EclipseWise.com websites. For a discussion about this, see:
http://www.eclipsewise.com/lunar/LEhelp/LEenlargement.html
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Curt Renz
April 1, 2015 at 11:31 am
Fred, like you and our mutual friend Jean Meeus, I use the French Rule for shadow enlargement. However, Jean and apparently you assume for eclipse predictions that the Earth is perfectly spherical and the umbra is perfectly circular. I take into account the oblate shape of the Earth and the resultant elliptical umbra. For the positions of the Sun and Moon I employ the ultra-accurate numerical integration program Solex. As a result I find the upcoming lunar eclipse to not be total, but to be partial with a magnitude of +0.995. Jean has conceded to me that if the true shape of the Earth is considered, the eclipse should be deemed partial.
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Fred Espenak
April 2, 2015 at 9:55 am
You bring up an interesting point. My calculations include a simple correction for Earth's oblateness at a latitude of 45°. This plus the use of Danjon's method for defining the shadow diameters results in a total phase lasting 4.5 minutes. It also reveals that the northern limb of the Moon lies within just 2 arc-seconds of the umbra's edge. It's possible that a more detailed model for the oblateness of the umbral shadow could place the Moon's northern limb on the edge or even outside of the umbra. So the April 4 eclipse is a very interesting test case. Unfortunately, the edge of the umbral shadow may be too diffuse for us to observationally determine whether the eclipse is a very short total or a very deep partial. The weather forecast in Arizona is promising so I will be watching and imaging.
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Fred Espenak
April 1, 2015 at 11:04 am
I've posted a lot more information about this eclipse on the new eclipse predictions website EclipseWise.com:
http://www.eclipsewise.com/lunar/LEnews/TLE2015Apr04/TLE2015Apr04.html
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Larry-Koehn
April 1, 2015 at 4:59 pm
I have spoken to the people at USNO about there eclipse timings, and they feel very confident about what they release and feel their model is current. They never comment on other people's work as "older way." Everyone has their own idea of what the eclipse timings are. Try to get anyone to get together to work out their differences and come up with an agreeable model - no way! I tried getting Sky & Telescope to look into the discrepancies in eclipse calculations: There answer was to "live with the ambiguities!" Why? So when the August 2017 TSE comes around Sky & Telescope, whose data are you going with and why? I hate ambiguities!
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Helio C. Vital
April 3, 2015 at 12:28 pm
Based on our statistics of 30 lunar eclipses and more than seven thousand published crater and limb
timings, I have calculated a 95% chance that this eclipse will be total. Our predictions use rigorous
models of the umbra based on the geoid published by Souslby and also by Sinnott&Herald (last year)
and have mostly agreed within +-0.3 min. (1 sigma) with 2,140 contact timings made by ourselves
(REA/BRAZIL) and others. Also, our algorithms and computer programs have been empirically tested for over 15 years now and have yielded atmospheric umbral enlargement factors in good agreement (usually better than 0.1%) with those calculated by Roger Sinnott. My feeling is that, apart from using an acurate model to describe the umbra, the variability of the atmospheric contribution to the size of the umbra is actually the major source of uncertainty in predictions. For the eclipse on April 4, I have calculated that if it is less than 1.25% (or 1.6 sigma below our 1.34+-0.06% mean of 30 observed eclipses) of the moon`s equatorial horizontal parallax, then a deep partial eclipse will occur. In fact, although the chance of that happening is indeed small, only 1 in 20, it is not negligible at all. Thus contact timings of this very special event are really welcomed since the fuzzy border of the umbra may make it quite difficult to tell when or even if the lunar disc was completely hidden inside the darker region of Earth`s shadow. Finally, regarding its brightness, the moon`s path inside the umbra being practically as shallow as possible for a total eclipse, added to the fact that major volcanic explosions have not occurred recently and thus the stratosphere is mostly clean, will probably render this eclipse as bright as a total lunar eclipse can be. Thus our prediction for the moon`s visual magnitude at mid-eclipse is m=-3.5+-0.3. For more information, please visit our Lunissolar2003 eclipse pages at
http://www.geocities.ws/lunissolar2003 or directly our article at
http://www.geocities.ws/lunissolar2003/2015_Apr04_Lunar_Eclipse.htm .
Thank you for your attention and good observing to everyone.
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April 4, 2015 at 10:14 pm
It started before I awoke in Albuquerque, nm. At 4:45am mountain time 1/2 the moon was eclipsed. It took till 6:00 am to completely cover and eclipse. The upper right side remained lit like a hat for about 30 minutes before the moon dropped rapidly from 60 degrees to 15 degrees above the horizon volcanoes. The moon did achieve full eclipse here, but was visible grey while opaqued. It was amusing like a piece of fruit in a tree hanging from its bough in the morning just before sunrise. The weather grew cold on Wednesday here in 40s in night and 50s in morning. The sun rise was blue at 6:10. I went back to sleep and at 9am white clouds coveted the sky. They broke up by 11am and returned by 5pm. I believe there is a water source drawn in from the gulf of new mexico into the chaco canyon area causing this damp clouding on full moon mornings. Its dry when the moon is high and damp when falling and afterwards. The pain in your scull isd real here at 6,000 feet and big bats and wolves do wander about for believers in that stuff.
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Graham-Wolf
April 8, 2015 at 8:22 pm
Hi Fred (Dr Eclipse)
Great to hear from you again... and your blogs!
"Pseudo-totality" from the Barber Grove Observatory at Lower Hutt, NZ, was some 10.5 minutes.
Thin 30 x 400km sliver of intense white along the bottom limb (terrestrial orientation). Interesting Danjon estimates (quite darker than last October). Used a 26cm f4.9 GSO 1/16 wave dielectric Dobbie with GSO SV15 eyepiece and corresponding 2 inch 2x ED Barlow.
Excellent clear skies with a 20 kt Northerly. Yes... got to see Nova Sgr AND Mv 9 NGC 4697 (galaxy in Virgo) during mid-eclipse. Last October, I observed (as did Chris Wyatt of Walcha, NSW) 4 faint comets during then totality.
Hope you soon "un-retire" back to NASA-Goddard... keep up the awesome work, Fred. You're still an impressive inspiration to us "Eclipse chasers" out there!
Graham W. Wolf:-
Barber Grove Observatory, Lower Hutt, NZ
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Graham-Wolf
April 11, 2015 at 11:06 pm
Hi all.
An updated correction.
I sill (respectfully) rate the Eclipse as a near Total.
Using software ("Virtual Moon Atlas"), field sketches, and some charts by Rukil to cross check... I now have to say...
1. Using Plato as a 100km "measure", the lit "sliver" at "Totality" appears to be more like 1800 x 100km +/- 20%.
2. The sliver was further back (towards the limb) than Endymion which was the last significant crater that I successfully timed in Ingress. From NZ, the sliver was orientated (to the naked eye) at the bottom edge... i.e. 5 o'clock to 7 o'clock.
3. Anaxagoras was NOT shadowed, neither was Meton..
4. All of Mare Frigoris was shadowed.
5. The sliver appeared to be approx. 150% of the diameter of Mare Imbrium, in total length.
6. The craters at each end of the sliver appeared to be ...
(a) Pythagoras (133km diam) at 62.8 W 63.5 N.
(b) De La Rue (139km diam) at 53.0 E 59.1 N.
And, whilst ball this was happening, several HIP stars entered behind the limb of the Moon during the Eclipse. Did you notice any of these???
Hope this helps settle the "Totality" issue.
First and last umbral contacts appeared to be well within a few seconds of prediction, as were the crater timings themselves. From my own NZ location, the Moon was some 50 deg alt in NE, and approx. 2/3 of the way along a line between Spica and Porrima in Virgo.
Regards to all who observed it....
Good luck with the number-crunching Fred (Dr Espenak)!
Graham W. Wolf:-
Barber Grove Observatory, Lower Hutt, New Zealand.
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