The November 8th total lunar eclipse spans the Pacific and is the last until 2025.
Set your alarms: if skies cooperate, next Tuesday morning’s lunar eclipse on November 8th is worth getting up for and braving the cold. Not only is this one of the top astronomical events for 2022, but it’s also the last total lunar eclipse for a while…until, in fact, March 14, 2025.
Friday morning’s partial lunar eclipse will flirt with with totality, as the longest for more than a century.
If you’re like us, we never miss a chance to catch a lunar eclipse, be it penumbral, partial or total. Lunar eclipses are a great time to catch the surety of the clockwork Universe at its best, as the Moon slides into and then exits the Earth’s shadow.
First the bad news: Friday morning’s eclipse in the early hours of November 19th isn’t completely total. However, the good news is that at its maximum around 9:04 Universal Time (UT)/4:04 AM Eastern Time (EST) the eclipse narrowly misses totality, at 97.5% partial.
By now, you’ve heard the news. One of the top astronomy events for 2019 is coming right up on the night of January 20th into the morning of the 21st with a total eclipse of the Moon. There’s lots of hype circulating around this one, as it assumes the meme of the “SuperBloodWolf Moon eclipse” ’round ye ole web.
One of the top astronomy events of 2018 occurs on the evening of Friday, July 27th, when the Moon enters the shadow of the Earth for a total lunar eclipse. In the vernacular that is the modern internet, this is what’s becoming popularly known as a “Blood Moon,” a time when the Moon reddens due to the refracted sunlight from a thousand sunsets falling upon it. Standing on the surface of the Moon during a total lunar eclipse (which no human has yet to do) you would see a red “ring of fire” ’round the limb of the eclipsed Earth.
This is the second total lunar eclipse for 2018, and the middle of a unique eclipse season bracketed by two partial solar eclipses, one on July 13th, and another crossing the Arctic and Scandinavia on August 11th.
The July 27th total lunar eclipse technically begins around 17:15 Universal Time (UT), when the Moon enters the bright penumbral edge of the Earth’s shadow. Expect the see a slight shading on the southwest edge of the Moon’s limb about 30 minutes later. The real action begins around 18:24 UT, when the Moon starts to enter the dark inner umbra and the partial phases of the eclipse begin. Totality runs from 19:30 UT to 21:13 UT, and the cycle reverses through partial and penumbral phases, until the eclipse ends at 23:29 UT.
Centered over the Indian Ocean region, Africa, Europe and western Asia get a good front row seat to the entire total lunar eclipse. Australia and eastern Asia see the eclipse in progress at moonset, and South America sees the eclipse in progress at moonrise just after sunset. Only North America sits this one out.
Now, this total lunar eclipse is special for a few reasons.
First off, we’ll have the planet Mars at opposition less than 15 hours prior to the eclipse. This means the Red Planet will shine at a brilliant magnitude -2.8, just eight degrees from the crimson Moon during the eclipse, a true treat and an easy crop to get both in frame. We fully expect to see some great images of Mars at opposition along with the eclipsed Moon.
How close can the two get? Well, stick around until April 27th, 2078 and you can see the Moon occult (pass in front of) Mars during a penumbral lunar eclipse as seen from South America.
And speaking of occultations, the Moon occults some interesting stars during totality Friday, the brightest of which is the +5.9 magnitude double star Omicron Capricorni (SAO 163626) as seen from Madagascar and the southern tip of Africa. Omicron Capricorni has a wide separation of 22″.
The second unique fact surrounding this eclipse is one you’ve most likely already heard: it is indeed the longest one for this century… barely. This occurs because the Moon reaches its descending node along the ecliptic on July 27th at 22:40 UT, just 21 minutes after leaving the umbral shadow of the Earth. This makes for a very central eclipse, nearly piercing the umbral shadow of the Earth right through its center.
Totality on Friday lasts for 1 hour, 42 minutes and 57 seconds. This was last beat on July 16th, 2000 with a duration of 1 hour, 46 minutes and 24 seconds (2001 is technically the first year of the 21st century). The duration for Friday’s eclipse won’t be topped until June 9th 2123 (1 hour 46 minutes six seconds), making it the longest for a 123 year span.
The longest total lunar eclipse over the span of 5,000 years from 2000 BC to 3000 AD was on May 31st, 318 AD at 106.6 minutes in duration.
A Minimoon Eclipse
Finally, a third factor is assisting this eclipse in its longevity is the onset of the MiniMoon: The Moon reaches apogee at July 27th, 5:22 UT, 14 hours and 37 minutes prior to Full and the central time of the eclipse. This is the most distant Full Moon of the year for 2018 (406,222 km at apogee) the 2nd most distant apogee for 2018. Apogee on January 15th, beats it out by only 237 kilometers. This not only gives the Moon a slightly smaller size visually at 29.3′, versus 34.1′ near perigee, less than half of the 76′ arcminute diameter of the Earth’s shadow. This also means that the Moon is moving slightly slower in its orbit, making a more stately pass through the Earth’s shadow.
What will the Moon look like during the eclipse? Not all total lunar eclipses are the same, but I’d expect a dark, brick red hue from such a deep eclipse. The color of the Moon during a eclipse is described as its Danjon number, ranging from a bright (4) to dark murky copper color (0) during totality.
Tales of the Saros
This particular eclipse is member 38 of the 71 lunar eclipses in saros series 129, running from June 10th, 1351 all the way out to the final eclipse in the series on July 24th, 2613 AD. If you caught the super-long July 16th, 2000 eclipse (the longest for the 20th century) then you saw the last one in the series, and the next one for the series occurs on August 7th, 2036. Collect all three, and you’ve completed a triple exeligmos series, a fine word in Scrabble to land on a triple word score.
Photographing the Moon
If you can shoot the Moon, you can shoot a total lunar eclipse, though a minimum focal length lens of around 200mm is needed to produce a Moon much larger that a dot. The key moment is the onset of totality, when you need to be ready to rapidly dial the exposure settings down from the 1/100th of a second range down to 1 second or longer. Be careful not to lose sight of the Moon in the viewfinder all together!
Are you watching the eclipse during moonrise or moonset? This is a great time to shoot the eclipsed Moon along with foreground objects… you can also make an interesting observation around this time, and nab the eclipsed Moon and the Sun above the local horizon at the same time in what’s termed a selenelion. This works mainly because the Earth’s shadow is larger than the apparent diameter of the Moon, allowing it to be cast slightly off to true center after sunrise or just before sunset. Gaining a bit of altitude and having a low, flat horizon helps, as the slight curve of the Earth also gives the Sun and Moon a tiny boost. For this eclipse, the U2-U3 umbral contact zone for a selenelion favors eastern Brazil, the UK and Scandinavia at moonrise, and eastern Australia, Japan and northeastern China at moonset.
Incidentally, a selenelion is the second visual proof you see during a lunar eclipse that the Earth is indeed round, the first being the curve of the planet’s shadow seen at all angles as it falls across the Moon.
Another interesting challenge would be to capture a transit of the International Space Station during the eclipse, either during the partial or total phases… to our knowledge, this has never been done during a lunar eclipse. This Friday, South America gets the best shots at a lunar eclipse transit of the ISS:
Live on the wrong continent, or simply have cloudy skies? Gianluca Masi and the Virtual Telescope Project 2.0 have you covered, with a live webcast of the eclipse from the heart of Rome, Italy on July 27th starting at 18:30 UT.
Be sure to catch Friday’s total lunar eclipse, either in person or online… we won’t have another one until January 21st, 2019.
Learn about eclipses, occultations, the motion of the Moon and more in our new book: Universe Today’s Guide to the Cosmos: Everything You Need to Know to Become an Amateur Astronomer now available for pre-order.
On Wednesday, January 31st (i.e. today!), a spectacular celestial event occurred. For those who live in the western part of North America, Alaska, and the Hawaiian islands, it was visible in the wee hours of the morning – and some people were disciplined enough to roll out of bed to see it! This was none other than the highly-anticipated “Super Blue Moon“, a rare type of full moon that on this occasion was special for a number of reasons.
For one, it was the third in a series of “supermoons”, where a Full Moon coincides with the Moon being closer in its orbit to Earth (aka. perigee) and thus appears larger. It was also the second full moon of the month, which is otherwise known as a “Blue Moon“. Lastly, for those in right locations, the Moon also passed through the Earth’s shadow, giving it a reddish tint (known as a “Red Moon” or “Blood Moon”).
In short, you could say that what was occurred this morning was a “super blue blood moon.” And as you can see, some truly awesome pictures were taken of this celestial event from all over the world. Here is a collection of pictures that a number of skilled photographers and star gazers have chosen to share with us. Enjoy!
“Thanks to everyone who used the #universetoday hashtag on Instagram to let us know about your pictures. There are many many more in there, so check it out.”
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.
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 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.
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…
Do you welcome the extra evening light of the Full Moon, or curse the additional light pollution? Either way, this week’s Full Moon on Friday April 22nd is special. It’s the smallest Full Moon of 2016, something we here at Universe Today have christened the Mini-Moon.
Mini-Moon 2016: This year’s Mini-Moon falls on April 22nd at 5:25 Universal Time (UT), just 13 hours and 19 minutes after lunar apogee the evening prior at 16:06 UT on April 21st. Though apogee on the 21st is 406,350 km distant – a bit on the far end, but the third most distant for the year by 300 km — this week’s Full Moon is the closest to apogee for 2016 time-wise. The 2015 Mini-Moon was even closer, in the 10 hour range, but you’ll have to wait until December 10th, 2030 to find a closer occurance.
What is the Mini-Moon, you might ask? As with the often poorly defined Supermoon, we like to eschew the ambiguous ‘90% of its orbit’ definition, and simply refer to it as a Full Moon occurring within 24 hours of lunar apogee, or its farthest point from the Earth in its orbit.
Fun fact: the 29.55 day period from perigee to perigee (or lunar apogee-to-apogee) is known as an anomalistic month.
Thank our Moon’s wacky orbit for all this lunacy. Inclined 5.14 degrees relative to the ecliptic plane, the Moon returns to the same phase (say, Full back to Full) every 29.53 days, known as a synodic month. The Moon can appear 33.5′ across during perigee, and shrink to 29.4′ across near apogee.
And don’t fear the ‘Green Moon,’ and rumors going ’round ye’ ole internet that promise a jaded Moon will occur in April or May; this is 100% non-reality based, seeking to join the legends of Super, Blood, and Full Moons, Black and Blue.
The April Full Moon is also known as the Full Pink Moon to the Algonquin Indians. The April Full Moon, can, on occasion be the Full Moon ushering in Easter (known as the Paschal Moon) as per the rule established by the 325 AD council of Nicaea, stating Easter falls on the first Sunday after the first Full Moon after the fixed date of the Vernal Equinox of March 21st. Easter can therefore fall as late as April 25th, as next occurs on 2038. The future calculation of Easter by the Church gets the Latin supervillain-sounding name of Computus.
Of course, the astronomical vernal equinox doesn’t always fall on March 21st, and to complicate matters even further, the Eastern Orthodox Church uses the older Julian Calendar and therefore, Easter doesn’t always align with the modern western Gregorian calendar used by the Roman Catholic Church.
The Moon can create further complications in modern timekeeping as well.
Here’s one wonderful example we recently learned of in our current travels. The Islamic calendar is exclusively based on the synodic cycle of the Moon, and loses 11 days a year in relation to the Gregorian solar calendar. Now, Morocco officially adopted Daylight Saving (or Summer) Time in 2007, opting to make the spring forward during the last weekend of March, as does the European Union to the north. However, the country reverts back to standard time during the month of Ramadan… otherwise, the break in the daily fast during summer months would fall towards local midnight.
You can see a curious future situation developing. In 2016, Ramadan runs from sundown June 5th, to July 4th. Each cycle begins with the sighting of the thin waxing crescent Moon. However, as Ramadan falls earlier, you’ll get a bizarre scenario such as 2022, when Morocco springs forward on March 27th, only to fall back to standard time six days later on April 2nd on the start of Ramadan, only to jump forward again one lunation later on April 30th!
Morocco is the only country we’ve come across in our travels that follows such a convoluted convention of timekeeping.
And the Spring Mini-Moon sets us up for Supermoon season six months later this coming October-November-December. Though lunar perigees less than 24 hours from Full usually occur as a trio, an apogee less than 24 hours from Full is nearly always a solitary affair, owing to the slightly slower motion of the Moon at a farther distance.
Don’t miss the shrunken Mini-Moon rising on the evenings of Thursday April 21st and Friday 22nd, coming to a sky near you.
Brace yourselves for Blue Moon madness. The month of July 2015 hosts two Full Moons: One on July 2nd and another coming right up this week on Friday, July 31st at 10:43 Universal Time (UT)/6:43 AM EDT.
In modern day vernacular, the occurrence of two Full Moons in one calendar month has become known as a ‘Blue Moon.’ This is a result of the synodic period (the amount of time it takes for the Moon to return to a like phase, in this case Full back to Full) of 29.5 Earth days being less than every calendar month except February.
In the ‘two Full Moons in one month’ sense, the last time a Blue Moon occurred was on August 31st, 2012, and the next is January 31st, 2018. The next time a Blue Moon occurs in the month of July is 2034, and the last July Blue Moon was 2004.
We say “once in a blue Moon,” as if it’s a rarity, but as you can see, they’re fairly frequent, occurring nearly once every 2-3 years or so.
Now, we’ll let you in on a secret. Like its modern internet meme cousin the ‘Super-Moon,’ astronomers don’t sit in mountain top observatories discussing the vagaries of the Blue Moon. In fact, astronomers rarely like to observe during the weeks surrounding the light-polluting Full Moon, and often compile data from the comfort of their university offices rather than visit mountaintop observatories these days…
The modern Blue Moon is now more of a cultural phenomenon. We’ve written previously about how an error brought us to the current ‘two Full Moons in one month definition.’ A more convoluted old timey definition was introduced in ye ole Maine Farmer’s Almanac circa 1930s as “the third Full Moon in an astronomical season with four.”
Legend has it that the Maine Farmer’s Almanac denoted this pesky extra seasonal Full Moon with ‘blue’ instead of black ink… to our knowledge, no examples exist to support this intriguing tale. Anyone have any old almanacs in the attic holding such a revelation out there?
Of course, the Moon most likely won’t appear to be physically blue, no matter what friends/family/co-workers/anonymous persons on Twitter say. The Moon can actually appear blue, as it did on September 23rd, 1950 for much of the eastern United States and Canada through the haze of several forest fires in western Canada. The Moon was actually at waxing gibbous phase on the evening of this phenomenon, and as far as we can tell, no photographic documentation of this event exists. Spaceweather, has, however gathered a gallery of blue moon eyewitness reports over the years, including a few images. This occurs when moonlight is filtered through suspended oil drops about a micrometer in diameter which scattered yellow and red light, leaving a Moon with a ghostly indigo glow.
So there’s definitely another challenge to catch and photograph a truly ‘Blue Moon’ under such rare atmospheric circumstances… and remember, the Moon doesn’t have to be near Full to do it!
Watch that Moon, as we’ve got a few red letter dates coming up through the remainder of 2015. First up: the Supermoon season cometh in August, as we have a series of three Full Moons falling less than 24 hours from perigee on August 29th, September 28th, and October 27th. Our money is on that middle one as having the potential to generate the most online lunacy, as it’s also the last total lunar eclipse of the current tetrad of four total lunar eclipses for 2014 and 2015, a ‘super-blood moon eclipse’ anyone? Though the dead won’t rise from the grave to mark such an occasion, you can be sure that many a sky aficionado will stumble zombie-like into the office the next day after pulling an all-nighter for the last good North American total lunar eclipse until 2018.
And it’s worth noting the path of the Moon, as it reaches its shallow mid-point in the last half of 2015. The Moon’s orbit is tilted about five degrees relative to the ecliptic, meaning that it can ride anywhere from 18 degrees—as it does this year—to 28 degrees from the celestial equator. This cycle takes about 19 years to complete, and a wide-ranging ‘long nights Moon’ last occurred in 2006, and will next occur in 2025.
So don’t fear the Blue Moon, but be sure to take a stroll under its light this coming Friday… and perhaps enjoy a frosty Blue Moon beer on the eve of the sultry month of August.
Millions of viewers across the western United States and across the Pacific, to include Australia and New Zealand were treated to a fine Easter weekend lunar eclipse on Saturday. And while this was the third of the ongoing tetrad of four lunar eclipses, it was definitely worth getting up early for and witnessing firsthand.
But was it truly total at all?
To Recap: The April 4th eclipse featured the shortest advertised duration for totality for the 21st century, clocking in at just four minutes and 43 seconds in length. In fact, you’d have to go all the way back to 1529 to find a shorter span of totality, at one minute and 42 seconds. And you’ll have to wait until September 11th, 2155 to find one that tops it in terms of brevity.
A fascinating discussion as to whether this was a de facto total lunar eclipse has recently sprung up on the message boards and a recent Sky and Telescopearticle online.
It all has to do with how you gauge the shape and size of the Earth’s shadow.
This is a surprisingly complex affair, as the Earth’s atmosphere gives the umbra a ragged and indistinct edge. If you’ve ever taken our challenge to determine your longitude using a lunar eclipse — just as mariners such as Christopher Columbus did while at sea — then you know how tough it is to get precise contact timings. There has been an ongoing effort over the years to model the size changes in Earth’s shadow using crater contact times during a lunar eclipse.
Many observers have commented in forums and social media that the northern limb of the Moon stayed pretty bright throughout the brief stretch of totality for Saturday’s eclipse.
“There are 3 ways of computing the magnitude of a lunar eclipse,” Eclipse expert David Herald mentioned in a recent Solar Eclipse Message List (SEML) posting:
The ‘traditional’ way as used in the Astronomical Almanac is attributed to Chauvenet – where the umbral radius is increased by a simple 2% – with the radius being based on the Earth’s radius at 45 deg latitude (and otherwise the oblateness of the Earth is ignored). For this eclipse the Chauvenet magnitude was 1.005.
The second way (used in the French Almanac, and more recently by Espenak & Meeus in their ‘Five Millennium Canon of Lunar Eclipses’ is the Danjon method. It similarly uses the Earth’s radius at 45 deg (and otherwise the oblateness is ignored), and increases the Earth’s radius by 75km. For this eclipse the Danjon magnitude is 1.001
The most recent approach (Herald & Sinnott JBAA 124-5 pgs 247-253, 2014) is based on the Danjon approach; however it treats the Earth as oblate, allows for the varying inclination of the Earth relative to the Sun during the year, and increases the Earth’s radius by 87km – being the best fit to 22,539 observations made between 1842 and 2011. For this eclipse the magnitude is computed as 1.002.
“As for eclipses, to me it is total when sliver of light comes through the edge of the Earth’s profile,” eclipse chaser Patrick Poitevin told Universe Today. “Once a minimum of light passes through any of the lunar dales (as it does during a total solar eclipse) I do not concede it as a total. Same for a lunar eclipse.”
This is a complex question because the shape of the Earth’s umbra upon the Moon is diffuse due to the effects of the Earth’s atmosphere. The various models used (with corrected radii for the Earth) are empirically based on crater timings of past lunar eclipses, of which there is some uncertainty. I’m sure this accounted for the difference between the USNO duration of eclipse and NASA.
The comment (in the recent Sky & Telescope post online) by Curt Renz is valid; correcting for the Earth’s flattening (meaning that the Earth’s radius from pole to pole is about a third of a percent shorter than the radius across the equator) might influence whether this very low magnitude eclipse is total or not. I haven’t made the calculation whether the Earth’s flattening tips this eclipse from total to partial, but it’s plausible.
There is another wrinkle: due to parallactic shifts of the Moon when observing from either pole of the Earth, it might be that for a lunar eclipse right on the knife edge of total/partial, that it may indeed be total from one polar region and partial from another. This is a kind of libration, but it would be a very subtle difference and probably unobservable.
It is only possible to conclusively define Saturday’s eclipse as total or partial if you define a brightness threshold for the Sun’s photosphere illuminating an edge of the Moon. The problem here is that this line is indistinct and fuzzy. I watched the lunar eclipse carefully with this question in mind and I could not decide for myself whether this lunar eclipse was total or partial. I think it would require a photometer to make this distinction.
Certainly, there’s little record of just how the 102 second long lunar eclipse of 1529 appeared. Ironically, it too was a total eclipse near sunrise as seen from Europe. On the other side of the coin, the deep partial eclipse of August 26th, 1961 just missed totality at 98.6% obscuration… and the two lunar eclipses in 2021 have similar circumstances, with a barely total lunar eclipse just 15 minutes long on May 26th and a 97.4% partial lunar eclipse on November 19th.
So maybe we won’t have to wait until 2155 to see another brief lunar eclipse that blurs the lines and refuses to play by the rules.
What do you, the readers think? What did you see last Saturday morn, a bright total lunar eclipse, or a deep partial?
Boy, how about that total solar eclipse last Friday? And there’s more in store, as most of North America will be treated to yet another total lunar eclipse on the morning of April 4th. This eclipse is member three of four of a quartet of lunar eclipses, known as a tetrad.
Solar and lunar eclipses are predictable, and serve as a dramatic reminder of the clockwork nature of the universe. Many will marvel at the ‘perfect symmetry’ of eclipses as seen from the Earth, though the true picture is much more complex. Yes, the Sun is roughly 400 times larger in diameter than the Moon, but also about 400 times farther away. This distance isn’t always constant, however, as the orbits of both the Earth and Moon are elliptical. And to complicate matters, the Moon is currently moving 3 to 4 centimetres farther away from the Earth per year. Already, annular eclipses are more common in the current epoch than are total solar eclipses, and about 1.4 billion years from now, total solar eclipses will cease to happen entirely.
This has an impact on lunar eclipses as well. The dark inner umbra of the Earth is an average of about 1.25 degrees across at the distance from Earth to the Moon. The Moon’s orbit is inclined 5.1 degrees relative to the ecliptic plane, which traces out the Earth’s path around the Sun. If this inclination was equal to zero, we’d be treated to two eclipses — one solar and one lunar — every 29.5 day synodic month.
This inclination assures that we have, on average, two eclipse seasons year, and that eclipses occur in groupings of 2-3. The maximum number of eclipses that can occur in a calendar year is 7, which next occurs in 2038, and the minimum is 4, as occurs in 2015.
A solar eclipse occurs at New Moon, and a lunar eclipse always occurs at Full — a fact that many works of film and fiction famously get wrong. And while you have to happen to be in the narrow path of a solar eclipse to witness totality, the whole Moonward facing hemisphere of the Earth gets to witness a lunar eclipse. Ancient cultures recognized the mathematical vagaries of the lunar and solar cycles as they attempted to reconcile early calendars. Our modern Gregorian calendar strikes a balance between the solar mean and tropical year. The Muslim calendar uses strictly lunar periods, and thus falls 11 days short of a 365 day year. The Jewish and Chinese calendars incorporate a hybrid luni-solar system, assuring that an intercalculary ‘leap month’ needs to be added every few years.
But trace out the solar and lunar cycles far enough, and something neat happens. Meton of Athens discovered in the 5th century BC that 235 synodic periods very nearly equals 19 solar years to within a few hours. This means that the phases of the Moon ‘sync up’ every 19-year Metonic cycle, handy if you’re say, trying to calculate the future dates for a movable feast such as Easter, which falls on (deep breath) the first Sunday after the first Full Moon after the March equinox.
But there’s more. Take a period of 223 synodic months, and they sync up three key lunar cycles which are crucial to predicting eclipses;
Synodic month- The time it takes for the Moon to return to like phase (29.5 days).
Anomalistic month- The time it takes for the Moon to return to perigee (27.6 days).
Draconic month- the time it takes for the Moon to return to a similar intersecting node (ascending or descending) along the ecliptic (27.2 days).
That last one is crucial, as eclipses always occur when the Moon is near a node. For example, the Moon crosses ascending node less than six hours prior to the start of the April 4th lunar eclipse.
And thus, the saros was born. A saros period is just eight hours shy of 18 years and 11 days, which in turn is equal to 223 synodic, 242 anomalistic or 239 draconic months.
The name saros was first described by Edmond Halley in 1691, who took it from a translation of an 11th century Byzantine dictionary. The plural of saros is saroses.
This also means that solar and lunar eclipses one saros period apart share nearly the same geometry, shifted 120 degrees in longitude westward. For example, the April 4th lunar eclipse is member number 30 in a cycle of 71 lunar eclipses belonging to saros series 132. A similar eclipse occurred one saros ago on March 24th, 1997. Stick around until April 14th, 2033 and you’ll complete a personal triple saros of eclipses, known as an exeligmos.
Dozens of saros series — both solar and lunar — are underway at any particular time.
But there’s something else unique about April’s eclipse. Though saros 132 started with a slim shallow penumbral eclipse way back on May 12th, 1492, this upcoming eclipse features the very first total lunar eclipse of the series. You can tell, as the duration of totality is a short 4 minutes and 43 seconds, a far cry from the maximum duration of 107 minutes that can occur during a central eclipse.
This particular saros cycle of eclipses will continue to become more central as time goes on. The final total lunar eclipse of the series occurs on August 2nd, 2213 AD, and the saros finally ends way out on June 26th, 2754.
Eclipses, both lunar and solar, have also made their way into the annuals of history. A rising partial eclipse greeted the defenders of Constantinople in 1453, fulfilling a prophecy in the mind of the superstitious when the city fell to the Ottoman Turks seven days later. And you’d think we’d know better by now, but modern day fears of the ‘Blood Moon‘ seen during an eclipse still swirl around the internet even today. Lunar eclipses even helped mariners get a onetime fix on longitude at sea: Christopher Columbus and Captain James Cook both employed this method.
All thoughts to ponder as you watch the April 4th total lunar eclipse. This eclipse will be visible for observers across the Pacific, the Asian Far East, Australia and western North America, after which you’ll have one more shot at total lunar eclipse in 2015 on September 28th. The next total lunar eclipse after that won’t be until January 31st 2018, favoring North America.