An Impalpable Penumbral Eclipse

penumbral eclipse

Hey, how ’bout that annular eclipse last week? Some great images flooded in to Universe Today, as the final solar eclipse for 2016 graced the African continent. This not only marked the start of the second and final eclipse season for 2016, but it also set us up for the final eclipse of the year next week.

The path of next week's penumbral eclipse through the Earth's shadow. Adapted from NASA/GSFC/F. Espenak.
The path of next week’s penumbral eclipse through the Earth’s shadow. Adapted from NASA/GSFC/F. Espenak.

We’re talking about the penumbral lunar eclipse coming up next week on September 16th, 2016. this sort of eclipse occurs when the Moon just misses the dark inner core (umbra) of the Earth’s shadow, and instead, drifts through its relatively bright outer cone, known as the penumbra. Though not the grandest show as eclipses go, astute observers should notice a subtle light tea-colored shading of the Full Moon, and perhaps the ragged dark edge of the umbra on the northwestern limb of the Moon as it brushes by around mid-eclipse.

The visibility map for next week's eclipse. Image credit: NASA/GSFC/Fred Espenak.
The visibility map for next week’s eclipse. Image credit: NASA/GSFC/Fred Espenak.

The entirety of the eclipse will be visible from the region surrounding the Indian Ocean on the evening of Friday, September 6th. Viewers in Australia, New Zealand and Japan will see the eclipse transpire at moonset, and the eclipse will get underway at moonrise for observers in western Africa and Europe.

The eclipse runs from first contact at 16:55 Universal Time (UT) to 20:54 UT when the Moon quits the Earth’s shadow almost four hours later. Mid-eclipse occurs at 18:55 UT, with the Moon 91% immersed in the Earth’s outer shadow.

Tales of the Saros

This particular eclipse is member 9 of the 71 lunar eclipses in saros series 147. This saros began on July 2nd 1890 and runs through to the final eclipse in the cycle on May 1st 2990. It will produce its very first partial eclipse next time around on September 28th 2034, and its first total lunar eclipse on June 6th, 2449.

Why penumbrals? Aren’t they the ultimate non-event when it comes to eclipses? Like with much of observational astronomy, a penumbral lunar eclipse pushes our skills as a visual athlete to the limit. Check out the waxing gibbous Moon the night before the eclipse, then the Moon the night of the event. If you didn’t know any better, could you tell the difference from one night to the next? Often, the camera can see what the eye can’t. Photographing the Moon before, during and after a penumbral eclipse will often bring out the subtle shading on post-comparison. You’ll want to photograph the Moon when its high in the sky and free of atmospheric distortion low to the horizon, which tends to discolor the Moon. Such a high-flying Moon during mid-eclipse favors the Indian Subcontinent this time around. We’ve yet to see a good convincing time-lapse documenting a penumbral eclipse, though such a feat is certainly possible.

See anything... shady going on? Here's the penumbral lunar eclipse from this past March. Image credit and copyright: Neeraj Ladia
See anything… shady going on? Here’s the penumbral lunar eclipse from this past March. Image credit and copyright: Neeraj Ladia

When is an eclipse… not an eclipse? By some accounts, the Moon underwent a very shallow penumbral one cycle ago on August 18th, 2016, though the brush past the shadow was so slight that many lists, including the NASA’s GSFC eclipse page omitted it. Three eclipses (a lunar partial and a penumbral, or two penumbrals and one solar) can occur in one eclipse season, if the nodes of the Moon’s orbit where it intersects the ecliptic fall just right. This last occurred in 2013, and will happen again in 2020.

And when there’s a lunar eclipse, there’s also a Full Moon. The September Full Moon is the Harvest Moon, providing a few extra hours of illumination to get the crops in. This year, the Harvest Moon falls just six days from the equinox on September 22nd, marking the start of astronomical Fall in the northern hemisphere and Spring in the southern. The relative ecliptic angle also ensures that moonrise only slides back by a slight amount each evening for observers in mid-northern latitudes around the Harvest Moon.

Can’t wait til the next eclipse? Well, 2017 has four of ’em: an annular on February 26th favoring South America, two lunars (another penumbral on February 11th and a partial on August 7th) and oh yeah, there’s a total solar eclipse crossing the United States on August 21st. And the next total lunar eclipse? The dry spell is broken on January 31st, 2018, when a total lunar eclipse favoring the Pacific Rim occurs. Yeah, we got spoiled with four back-to-back lunar eclipses during the Blood Moon tetrad of 2014-2015…

Read Dave Dickinson’s eclipse-fueled sci-fi tales Exeligmos, Shadowfall, The Syzygy Gambit and Peak Season.

Our Guide to the Bizarre April 29th Solar Eclipse

Will anyone see next week’s solar eclipse? On April 29th, an annular solar eclipse occurs over a small D-shaped 500 kilometre wide region of Antarctica. This will be the second eclipse for 2014 — the first was the April 15th total lunar eclipse — and the first solar eclipse of the year, marking the end of the first eclipse season. 2014 has the minimum number of eclipses possible in one year, with four: two partial solars and two total lunars. This month’s solar eclipse is also a rarity in that it’s a non-central eclipse with one limit. That is, the center of the Moon’s shadow — known as the antumbra during an annular eclipse — will juuuust miss the Earth and instead pass scant kilometres above the Antarctic continent.

The "footprint" of the April 29th solar eclipse. Credit:
The “footprint” of the April 29th solar eclipse. Credit: Eclipse predictions by Fred Espenak, NASA/GSFC.

A solar eclipse is termed “non-central with one limit” when the center of the Moon’s umbra or antumbra just misses the Earth and grazes it on one edge. Jean Meeus and Fred Espenak note that out of 3,956 annular eclipses occurring from 2000 BCE to 3000 AD, only 68 (1.7%) are of the non-central variety. An annular eclipse occurs when the Moon is too distant to cover the disk of the Sun, resulting in a bright “annulus” or “ring-of-fire” eclipse. A fine example of just such an eclipse occurred over Australia last year on May 10th, 2013. An annular eclipse crossed the United States on May 10th, 1994 and will next be seen from the continental U.S. on October 14th 2023. But of course, we’ll see an end the “total solar eclipse drought” long before that, when a total solar eclipse crosses the U.S. on August 21st, 2017!

An animated .gif of the April 29th eclipse. Credit: NASA/GSFC/A.T. Sinclair.
An animated .gif of the April 29th eclipse. Credit: NASA/GSFC/A.T. Sinclair.

The “centrality” of a solar eclipse or how close a solar eclipse comes to crossing the central disk of the Earth is defined as its “gamma,” with 0 being a central eclipse, and 1 as the center of the Moon’s shadow passing 1 Earth radii away from central. All exclusively partial eclipses have a gamma greater than 1. The April 29th eclipse is also unique in that its gamma is very nearly 1.000… in fact, combing the 5,000 year catalog of eclipses reveals that no solar eclipse from a period of 2000 B.C. to 3000 A.D. comes closer to this value. The solar eclipses of October 3rd, 2043 and March 18th, 1950 are, however very similar in their geometry. Guy Ottewell notes in his 2014 Astronomical Calendar that the eclipses of August 29th, 1486 and January 8th, 2141 also come close to a gamma of 1.000. On the other end of the scale, the solar eclipse of July 11th 1991 had a gamma of nearly zero. This eclipse is part of saros series 148 and is member 21 of 75. This series began in 1653 and plays out until 2987 AD. This saros will also produce one more annular eclipse on May 9th 2032 before transitioning to a hybrid and then producing its first total solar eclipse on May 31st, 2068. But enough eclipse-geekery. Do not despair, as several southern Indian Ocean islands and all of Australia will still witness a fine partial solar eclipse from this event. Antarctica has the best circumstances as the Sun brushes the horizon, but again, the tiny sliver of “annularity” touches down over an uninhabited area between the Dumont d’Urville and Concordia  stations currently occupied by France… and it just misses both! And remember, its astronomical fall headed towards winter “down under,” another strike against anyone witnessing it from the polar continent. A scattering of islands in the southern Indian Ocean will see a 55% eclipsed Sun. Circumstances for Australia are slightly better, with Perth seeing a 55% eclipsed Sun and Sydney seeing a 50% partial eclipse.

The view of the eclipse from multiple locations across the Australian continent at 7:00 UT on April 29th. Created by the author using Stellarium.
The view of the eclipse from multiple locations across the Australian continent at 7:00 UT on April 29th. Created by the author using Stellarium.

Darwin,  Bali Indonesia and surrounding islands will see the Moon just nick the Sun and take a less than 20% “bite” out of it. Observers in Sydney and eastern Australia also take note: the eclipse occurs low to the horizon to the west at sunset, and will offer photographers the opportunity to grab the eclipse with foreground objects. Viewing a partial solar eclipse requires proper eye protection throughout all phases. The safest method to view a partial solar eclipse is via projection, and this can be done using a telescope (note that Schmidt-Cassegrain scopes are bad choice for this method, as they can heat up quickly!) or nothing more sophisticated than a spaghetti strainer to create hundreds of little “pinhole projectors.”

A simulation of the view that no one will see: the annular eclipse one kilometre above latitude 71S longitude 131E above the Antarctic. Created using Stellarium.
A simulation of the view that no one will see: the annular eclipse as seen hovering one kilometre above the Antarctic at latitude 71S longitude 131E . Created using Stellarium.

And although no human eyes may witness the annular portion of this eclipse, some orbiting automated ones just might. We ran some simulations using updated elements, and the European Space Agency’s Sun observing Proba-2 and the joint NASA/JAXA Hinode mission might just “thread the keyhole” and will witness a brief central eclipse for a few seconds on April 29th: And though there’ll be few webcasts of this remote eclipse, the ever-dependable Slooh is expected to carry the eclipse on April 29th. Planning an ad hoc broadcast of the eclipse? Let us know! As the eclipse draws near, we’ll be looking at the prospects for ISS transits and more. Follow us as @Astroguyz as we look at these and other possibilities and tell our usual “tales of the saros”. And although this event marks the end of eclipse season, its only one of two such spans for 2014… tune in this October, when North America will be treated to another total lunar eclipse on the 8th and a partial solar eclipse on the 23rd… more to come! Send in those eclipse pics to the Universe Today Flickr community… you just might find yourself featured in this space!

Get Ready for the April 15, 2014 Total Lunar Eclipse: Our Complete Guide

 April the 15th: In the United States, it’s a date dreaded by many, as the date to file taxes – or beg for an extension – looms large. But this year, Tax Day gives lovers of the sky something to look forward to, as the first of four total lunar eclipses for 2014 and 2015 occurs on the night of April 14th/15th favoring North and South America.

The circumstances for the April 15th, 2105 eclipse.
The circumstances for the April 15th, 2014 eclipse. The top chart shows the path of the Moon through the umbra, and the bottom chart shows the visibility region (light to shaded areas) Click here for a technical description. Credit:  Eclipse Predictions by Fred Espenak, NASA/GSFC.

This marks the first total lunar eclipse visible from since December 10th 2011, which was visible at moonset from North America, and marks the start of the first of two eclipse seasons for 2014. Totality will last 1 hour, 17 minutes and 48 seconds, and will be visible in its entirety from the central Atlantic westward to eastern Australia. Unlike a total solar eclipse, which occurs along a narrow track, a total lunar eclipse can be viewed by the entire moonward facing hemisphere of the Earth.

Tracing the umbra: a mosaic of the December 2010 eclipse. Photos by author.
Tracing the umbra: a mosaic of the December 2010 eclipse. Photos by author.

The action begins at 4:37 Universal Time (UT)/12:37 AM EDT, when the Moon enters the western edge of the Earth’s shadow known as the penumbra. The Moon will be completely immersed in the penumbra by 5:58 UT/1:58 AM EDT, but don’t expect to see anything more than a faint tan shading that’s slightly darker on the Moon’s northeastern edge.

The real action begins moments later, as the Moon encounters the ragged edge of the umbra, or the inner core of the Earth’s shadow. When does the umbra first become apparent to you? Totality then begins at 7:06 UT/3:06 AM EDT and lasts until 8:24 UT/4:24 AM EDT, with mid-eclipse occurring just south of the center of the Earth’s shadow at 7:46 UT/3:46 AM EDT.

Finally, the eclipse ends as the Moon slides out of the penumbra at 10:37 UT/ 6:37 AM EDT.  Michael Zeiler (@EclipseMaps) has complied a fine video guide to the eclipse:

Field guide to the total lunar eclipse of April 14 – 15, 2014 from Michael Zeiler on Vimeo.

This eclipse is also notable for being part of a series of four lunar eclipses in 2014 & 2015, known as a “tetrad.” NASA eclipse expert Fred Espenak notes that this series of eclipses is also notable in that all four are visible in part or in their entirety from the United States. We’re in a cycle of 9 sets of tetrads for the 21st century, which began with the first set in 2003. Before that, you have to go all the way back to the 16th century for the last set of eclipse tetrads!

4AM EDT. Credit Starry Night Education software.
The position of the Moon within the Earth’s umbra on the morning of April 15th at 4AM EDT/8UT. Credit: Starry Night Education software.

For saros buffs, the April 15th eclipse is Member 56 of 75 of saros 122, which began on August 14th 1022 A.D. and runs out until a final penumbral eclipse of the series on October 29th, 2338. There are only two total eclipses left in this particular saros, one in 2032 and 2050. If you caught the total lunar eclipse of April 4th, 1996, you saw the last lunar eclipse in this same saros series.

Lunar eclipses have turned up at some curious junctures in history. For example, a lunar eclipse preceded the fall of Constantinople in 1453. A 2004 lunar eclipse also fell on the night that the Red Sox won the World Series after an 86 year losing streak, though of course, lunar eclipses kept on occurring during those losing years as well. Christopher Columbus was known to evoke an eclipse on occasion to get him and his crew out of a jam, and also attempted to use a lunar eclipse to gauge his position at sea using a method first described by Ptolemy while studying the lunar eclipse of September 20th, 331 B.C.

A handful of stars in the +8th to +12th magnitude range will be occulted by the eclipsed Moon as well. Brad Timerson of the International Occultation Timing Association (IOTA) has put together a list, along with graze line prospects across the United States. The brightest star to be occulted by the eclipsed Moon is +5th magnitude 76 Virginis across western South America and Hawaii:

Credit: Occult 4.0
The occultation footprint of 76 Virginis during the April 15th lunar eclipse. Credit: Occult 4.0

Note that the bright star Spica will be only just over a degree from the eclipsed Moon, and Mars will also be nearby, just a week past its 2014 opposition. And to top it off, Saturn is just one constellation to the east in Libra!

During the partial phases of the eclipse, watch for the Moon to take on a “Pacman-like” appearance. The Earth’s umbra is just under three times the size of the Moon, and the Greek astronomer Aristarchus of Samos used this fact and a little geometry to gauge the distance to our natural satellite in the 3rd century B.C.

As totality approaches, expect the innermost rim of the Moon to take on a ruddy hue. This is the famous “combination of all the sunrises and sunsets” currently underway worldwide as light is bent through the Earth’s atmosphere into its shadow. It’s happening every night, and during the totality of a lunar eclipse is the only chance that we get to see it.

4AM Credit: Stellarium
Looking to the southwest at 4 AM EDT from latitude 30 degrees north on the morning of April 15th. Credit: Stellarium.

You don’t need anything more sophisticated than the naked eye or “Mark 1 eyeball” to enjoy a lunar eclipse, though it’s fun to watch through binoculars or a low-power telescope field of view. One interesting project that has been ongoing is to conduct timings for the moment when the umbra contacts various craters on the Moon. It’s a curious mystery that the Earth’s shadow varies by a small (1%) but perceptible amount from one eclipse to the next, and efforts by amateur observers may go a long way towards solving this riddle.

Said color of the fully eclipsed Moon can vary considerably as well: the Danjon scale describes the appearance of the eclipsed Moon, from bright and coppery red (Danjon 4) to so dark as to almost be invisible (Danjon 0). This is a product of the amount of dust, volcanic ash and aerosols currently aloft in the Earth’s atmosphere.  During the lunar eclipse of December 9th, 1992 the Moon nearly disappeared all together, due largely to the eruption of Mount Pinatubo the year prior.

A lunar eclipse also presents a chance to nab what’s known as a Selenelion. This occurs when the Sun and the totally eclipsed Moon appear above the local horizon at the same time. This is possible mainly because the Earth’s shadow is larger than the Moon, allowing it to linger a bit inside the umbra after sunrise or before sunset. Gaining some altitude is key to making this unusual observation.  During the April 15th eclipse, selenelion sightings favor the Mid-Atlantic and Greenland where totality is underway at sunrise and eastern Australia, where the reverse is true at sunset.

Want to have a go at measuring the brightness or magnitude of the eclipsed Moon? Here’s a bizarre but fun way to do it: take a pair of binoculars and compare the pinpoint Moon during totality to the magnitude of a known star, such as Antares or Spica.

Note that to do this, you’ll first need to gauge the magnitude extinction of your particular binoculars: NASA’s got a table for that, or you could field test the method days prior on Venus, currently shining at a brilliant -4.2 in the dawn. Hey, what’s a $1,000 pair of image-stabilized binocs for?

And of course, weather prospects are the big question mark for the event. Mid-April weather for North America is notoriously fickle. We’ll be watching the Clear Sky Chart and Skippy Sky for prospects days before the eclipse.

Photography during an eclipse is fun and easy to do, and you’ll have the waxing gibbous Moon available to practice on days prior to event. Keep in mind, you’ll need to slow down those shutter speeds as the Moon enters into totality, we’re talking going down from 1/60th of a second down to ¼” pretty quickly. In the event of a truly dark eclipse, the Moon may vanish in the view finder all together. Don’t be afraid to step exposures up to the 1 to 4 second range in this instance, as you’ve got over an hour to experiment.

Photo by author
Our “eclipse hunting rig…” the DSLR is piggy-backed to shoot stills on the main scope, which will shoot video. Note that the “f/34 field stop” will most likely be removed!  Photo by author

Thus far, only one webcast for the eclipse has surfaced, courtesy of the venerable Slooh. We’ll most likely be doing a follow up roundup of eclipse webcasts as they present themselves, as well as a look at prospects for things like a transit of the ISS in front of the eclipsed Moon and weather forecasts closer to show time.

And speaking of spacecraft, China’s Chang’e 3 lander and Yutu rover will have a fine view of a solar eclipse overhead from their Mare Imbrium vantage point, as will NASA’s LRO and LADEE orbiters overhead. In fact, NASA hinted last year that the April 15th eclipse might spell the end of LADEE entirely…

And thus marks the start of eclipse season one of two for 2014. Next up will be a curious non-central annular solar eclipse over Antarctica on April 29th, followed by another total lunar eclipse on October 8th, and a fourth and final partial solar eclipse of the year for North America of October 23rd.

Watch this space and follow us on Twitter as @Astroguyz, as we’ll be “all eclipses, all the time,” for April… no new taxes guaranteed!

Next up: Heard the one about the Blood Moon? Yeah, us too… join us as we debunk the latest lunacy surrounding the eclipse tetrad!

–      Got pics of the lunar eclipse? Send ‘em in to Universe Today, as a post-eclipse photo round up is a very real possibility!