History Archives

September 15, 2015December 23, 2015 by David Dickinson

A Minor Lunar Standstill for 2015

Think you know the Moon? Whether you love our natural neighbor in space for the lunar and solar eclipses it provides, or you simply decide to ‘pack it in’ from deep sky observing on the weeks bookending Full phase — per chance to catch up on image processing — the Moon has provided humanity with a fine crash course in Celestial Mechanics 101.

Take the Moon’s path in the Fall of 2015 as a peculiar case in point. In fact, we’re nearing what’s known as a minor lunar standstill over the next lunation, the first of the 21^st century.

The term lunar standstill is kind of a misnomer. The Moon will continue in its orbit around the Earth like it always does. What’s interesting to note, however, is how shallow the apparent path of the Moon currently is with respect to the ecliptic this year. A technical lunar standstill – the point at which the Moon seems to reverse course from north to south and vice versa – occurs twice a lunation… but not all lunar standstills are created equal.

The path of the ecliptic vs the orbit of the Moon on ‘shallow’ and ‘steep’ years. Image credit: Dave Dickinson

The approximately five degree tilt of the Moon’s path around the Earth with respect to the path of the Earth around the Sun assures that the Moon can actually appear anywhere from 23.5 degrees (the tilt of the Earth’s axis with respect to the ecliptic) plus five degrees above or below the celestial equator, or 28.5 degrees declination north to south.

Such a ‘hilly year’ happens once every 18.6 years, and last occurred in 2006, and won’t take place again until 2025. This orbital phenomenon also results in what’s known as a ‘long nights moon’ when the Full Moon nearest the winter solstice rides high in the sky near the spot the summer Sun occupied six months earlier, and will do so again six months hence.

To quote Game of Thrones: “Winter is coming,” indeed.

Such is the wacky orbit of the Moon. Unlike the majority of natural satellites in the solar system, the inclination of the Moon’s orbit is not fixed in relation to its host planet’s (in this case, the Earth’s) equator, but instead, to the plane of its path around the Sun, that imaginary line known as the ecliptic. Hence, we say the Moon’s path is either steep and ‘hilly’ near a major lunar standstill, or shallow and almost flat-lined, like this year. In between years are sometimes termed ‘ecliptic-like’ and happen between standstills once every 9.3 years.

Why are the nodes of the ecliptic changing? The chief culprit is the gravitational pull of the Sun, which drags the nodes opposite in the Moon’s direction of travel once around full circle every 18.6 years. To confound things even more, the Moon’s line of apsides (the imaginary line bisecting its orbit from apogee to perigee) is moving in the opposite direction and completes one revolution every 8.85 years.

This also means that the Moon can wander off the beaten trail of the zodiac constellations well worn by the classical planets. The Moon can actually transit 18 constellations: the 12 familiar zodiacal constellations, plus Orion, Ophiuchus, Sextans, Corvus, Auriga and Cetus.

This, along with the 26,000 plus year precession of the equinoxes, also means that the stars the Moon can occult along its path are slowly changing as well.

There’s lots of evidence to suggest that ancient astronomers knew something of the cycle of lunar standstills as well. The modern term comes from archaeologist Alexander Thom’s 1971 book Megalithic Lunar Observatories. There is evidence to suggest Bronze Age cultures in the United Kingdom took note of the changing path of the Moon. The famous ‘Sun dagger’ rock alignment of Fajada Butte in Chaco Canyon, New Mexico may have also doubled as a similar sort of calendar that not only marked the yearly solstices and equinoxes, but longer periods of the cycles of the Moon as well.

Knowing the gear clock tick of the heavens gave cultures an edge, allowing them to predict when to sow, reap, hunt and prepare for the onset of winter.

The 2015 minor lunar standstill also impacts this years’ Full Harvest Moon as well. Ordinarily on most years, the evening angle of the ecliptic versus the eastern horizon near the autumnal equinox conspires to make the Moon seem to ‘freeze’ in its nightly path, rising scant minutes later on successive evenings. This effect is most dramatic as seen from mid-northern latitudes in September on years around the major lunar standstill.

Not so in 2015. The Full Harvest Moon occurs on September 28^th at 2:50 UT (10:50 PM EDT on the evening of the 27^th) about four and half days after the autumnal equinox. As seen from latitude 40 degrees north, however, the Moon will rise nearly 40 minutes later each successive evening. Check out these Moonrise times as seen from the U.S. capital near 39 degrees north latitude:

Washington D.C.

Sept 25^th 5:28 PM

Sept 26^th 6:09 PM

Sept 27^th 6:49 PM

Sept 28^th: 7:29 PM

Sept 29^th: 8:11 PM

As you can see, the minor lunar standstill of 2015 ameliorates the usual impact of the Harvest Moon… though we do have the final total lunar eclipse of 2015 to compensate.

SOHO Nears 3,000 Comet Discoveries

A fine sungrazer nears its doom as seen via SOHOs LASCO C2 camera. Image credit: NASA/ESA/SOHO/NRLSungrazers

It’s a discovery that could come any day now.

The Solar Heliospheric Observatory spacecraft known as SOHO is set to cross the 3,000 comet discovery threshold this month. Launched atop an Atlas II rocket on December 2^nd, 1995, SOHO is a joint NASA/ESA mission, and has observed the Sun now for almost 20 years from the sunward L1 lagrange point. That fact is amazing enough, as SOHO has already followed the goings on of our tempestuous host star for nearly two full solar cycles.

And though SOHO wasn’t initially designed as a comet hunter extraordinaire, it has gone on to discover far more comets than anyone—human or robotic.

soho_photo7 — SOHO on Earth. Image credit: NASA/ESA/SOHO

The U.S. Naval Research Laboratory’s (NRL) sungrazer website lists the discovery count as 2,987 as of July 31, 2015, with more comets awaiting verification daily. “In the past, SOHO has often discovered as many as four or five comets in a single day,” Karl Battams, a solar scientist at the NRL told Universe Today. “Suffice to say, it really could be any day now, given how close we are to 3,000! I actually expected it to be a month ago, so I’m surprised it’s dragging out like this. Predicting comets is fraught with uncertainty!”

Part of what gives SOHO an edge is its LASCO (the Large Angle and Spectrometric Coronagraph) C2 and C3 coronagraphs. With a field of view about 15 degrees wide, the C3 imager monitors the faint corona of the Sun, while blocking its dazzling disk. The corona is the pearly white outer atmosphere of the Sun, and is about half as bright as a Full Moon. On Earth, we only see the corona briefly during a total solar eclipse. SOHO routinely sees sungrazing comets ‘photobomb’ the view of its LASCO C3 camera, sometimes to the tune of more than 200 a year.

Comet NEAT makes its way through the field of view of SOHO's LASCO C2 camera in 2003. Image credit: NASA/ESA/NRL/Sungrazers — Comet NEAT makes its way through the field of view of SOHO’s LASCO C2 camera in 2003. Image credit: NASA/ESA/NRL/Sungrazers

SOHO has rewritten the history of sungrazers. How far we’ve come: flashback to 1979, and less than a dozen sungrazers were known, one being the famous Comet Ikeya-Seki in 1965. Early space-based platforms such as Solwind and SMM sported early coronagraphs, and paved the way for SOHO. Think about that for a moment; a vast majority of the cometary population of the solar system was simply sliding by, unobserved from the ground. And this was only a generation ago.

Most of what SOHO sees are what’s termed as Kreutz group sungrazers. First theorized by astronomer Heinrich Kreutz in 1888, SOHO has given researchers the ability to classify and characterize the orbits of these doomed comets. These sungrazers nearly always incinerate during their perihelion passage. C/2011 W3 Lovejoy was a famous exception, which passed about 140,000 kilometers from the surface of the Sun on December 16^th, 2011 and went on to become a fine southern hemisphere comet.

“We knew little of the Kreutz population, other than that it seemed there were ‘a few’ objects on the Kreutz path,” Battams said. “I would say that probably when the Sungrazer Project was launched in late 2000 was the point at which the team realized that this was something more than just seeing an occasional comet.”

The typical track of a Kreutz-group comet. Click here for the full diagram of C2/C3 tracks throughout the year. Image Credit: NASA/ESA/SOHO

Kreutz comets also have seasons and predictable directions of approach along the ecliptic as seen from SOHO’s point of view. Some periodic comets, such as 96P Machholz, — which orbits the Sun once every six years — have become old friends. To date, SOHO has observed 96P Machholz four times.

Upping the Comet Hunting Game

But here’s the amazing second half of the tale. Legions of dedicated amateurs make these discoveries, patiently combing over daily images sent back by SOHO. In many ways, SOHO has grown up with the rise of the internet. Think about it: what was your internet surfing experience like way back in 1995? Karl Battams at NRL relays these discoveries to the Central Bureau for Astronomical Telegrams, the clearing house for potential comet discoveries. Founded in 1882 and based at Harvard College Observatory since 1965, CBAT actually received its last ‘telegram’ announcing the possible discovery that would become Comet Hale-Bopp in 1995.

The rise of automated surveys and satellites such as SOHO has definitely upped the game. To date, the all-time human champ amongst comet hunters is Robert H. McNaught, with the discovery of 44 long-period and 26 short-period comets.

And I think we can all remember where we were on U.S. Thanksgiving Day 2013, as SOHO gave us a front row seat to the demise of Comet ISON. It’s been a roller coaster ride for sure, and it’s hard to imagine a time now when we didn’t have SOHO as a daily resource. Heck, it’s just fun to watch planets transit the field of view of SOHO, as they move from the dawn to dusk sky and back again.

Looking at the "SOHO Bump" and the rise of automated comet hunters in the early 21st century. Image credit: Dave Dickinson — Looking at the “SOHO Bump” and the rise of automated comet hunters in the early 21st century. Image credit: Dave Dickinson

Comet hunting via SOHO is fun and easy to do, though yes, there are lots of eyeballs out there looking, so you have some pretty dedicated competition. Patience is key, and there’s also a dedicated message board describing the latest discoveries and known objects entering the field of view that have already been identified.

“What’s the future of SOHO? “December is SOHO’s 20^th anniversary, so that’s another milestone,” Battams said. “Beyond that, who knows? Engineers designed SOHO to operate for two years, and with no intention of comet discovery; it has lasted 20 years and re-written the history books for comets. It remains the only coronagraph we have along the Sun-Earth line, so for space weather forecasting it remains a unique and valuable asset.”

Congrats, and be sure to follow Karl Battam’s @SungrazerComets account on Twitter… number 3,000 could be discovered any day now!

September 8, 2015December 23, 2015 by David Dickinson

Kicking Off Eclipse Season: Our Guide to the September 13th Partial Solar Eclipse

The March 11th, 2013 partial solar eclipse as seen from Saida, Lebanon. Image credit and copyright: Ziad El Zaatari

Eclipse season 2 of 2 for 2015 is nigh this weekend, book-ended by a partial solar eclipse on September 13^th, and a total lunar eclipse on September 28^th.

First, the bad news. This weekend’s partial solar eclipse only touches down across the very southern tip of the African continent, Madagascar, a few remote stations in Antarctica, and a few wind-swept islands in the southern Indian Ocean. More than likely, the only views afforded humanity by Sunday’s partial solar eclipse will come out of South Africa, where the eclipse will be about 40% partial around 5:30 Universal Time (UT).

It’s the curious circumstances surrounding the September 13^th eclipse that conspire to hide it from the majority of humanity. First, the Moon reaches its ascending node along the plane of the ecliptic at 4:38 UT on Monday, September 14^th, nearly 22 hours after New phase. The umbra, or dark inner core of the shadow of Earth’s Moon ‘misses’ the Earth, passing about 380 kilometres or 230 miles above the South Pole. The outer penumbra of the Moon’s shadow just brushes the planet Earth, assuring a 79% maximum obscuration of the Sun over Antarctica around 6:55 UT.

Second, the Moon also reaches its most distant apogee for 2015 on September 14^th at 11:29 UT, 406,465 kilometers from the Earth. This is just over 28 hours after New, assuring that the umbra of the Moon falls 25,000 kilometres short of striking the Earth. The eclipse would be an annular one, even if we were in line to see it.

Observers will see the eclipse begin at sunrise over South Africa and the Kalahari Desert, great for photography and catching the eclipse along with foreground objects. Observers will need to follow solar observing safety protocols during all stages of the eclipse. A high value neutral density filter will bring out the silhouette of foreground objects while preserving the image of the partially eclipsed Sun, but remember that such a filter is for photographic use only.

P1, or the first contact of the Moon’s penumbra with the Earth occurs on the morning of the 13^th over the Angola/South Africa border at 4:41 UT, and the shadow footprint races across the southern Indian Ocean to depart Earth near the Antarctic coast (P4) at 09:06 UT.

New Moon occurs on September 13^th at 6:43 UT, marking the start of lunation 1147.

For saros buffs, this eclipse is a part of saros series 125 (member 54 of 73). Saros 125 started on February 4^th, 1060 and produced just four total eclipses in the late 13^th and early 14^th centuries. Mark your calendars, as this saros will end with a brief partial eclipse on April 8^th, 2358. The final total eclipse for this particular saros crossed over central Europe on July 16^th, 1330, when an observation by monks near Prague noted “the Sun was so greatly obscured that of its great body, only a small extremity like a three night old Moon was seen.”

Missing out on the eclipse? The good folks over at Slooh have got you covered, with a live webcast set to start at 4:30 UT/12:30 AM EDT.

Planning an ad-hoc webcast of your own from the eclipse viewing zone? Let us know!

There are also some chances to nab the eclipse from space via solar observing satellites in low Earth orbit:

The European Space Agency’s Proba-2 will see eclipses on the following passes – 5:01 UT (partial)/6:31 UT (annular) 8:00 UT (partial).

And JAXA’s Hinode mission will see the same at the following times: 5:56 UT (Partial)/7:46 UT (partial). Unfortunately, there are no good circumstances for an ISS transit this time around, as the ISS never passes far enough south in its orbit.

Looking for more? You can always participate in the exciting pastime of slender moonspotting within 24 hours post or prior to the New Moon worldwide. This feat of extreme visual athletics favors the morning of Saturday, September 12^th to sight the slim waning crescent Moon the morning before the eclipse, or the evenings of September 13^th and 14^th, to spy the waxing crescent Moon on the evenings after.

And this eclipse sets us up for the grand finale: the last total lunar eclipse of the ongoing tetrad on September 28^th, visible from North America and Europe. And yes, the Moon will be near perigee to boot… expect Super/Blood Moon wackiness to ensue.

Watch for our complete guide to the upcoming lunar eclipse, with observational tips, factoids, eclipse lunacy and more!

August 26, 2015December 23, 2015 by David Dickinson

Ice Giants at Opposition

It seems as if the planets are fleeing the evening sky, just as the Fall school star party season is getting underway. Venus and Mars have entered the morning sky, and Jupiter reaches solar conjunction this week. Even glorious Saturn has passed eastern quadrature, and will soon depart evening skies.

Enter the ice giants, Uranus and Neptune. Both reach opposition for 2015 over the next two months, and the time to cross these two out solar system planets off your life list is now.

Aug 26 — Looking east at dusk in late August, as Uranus and Neptune rise. Image credit: Stellarium

First up, the planet Neptune reaches opposition next week in the constellation Aquarius on the night of August 31^st/September 1^st. Shining at magnitude +7.8, Neptune spends the remainder of 2015 about three degrees southwest of the +3.7 magnitude star Lambda Aquarii. It’s possible to spot Neptune using binoculars, and about x100 magnification in a telescope eyepiece will just resolve the blue-grey 2.3 arc second disc of the planet. Though Neptune has 14 known moons, just one, Triton, is within reach of a backyard telescope. Triton shines at magnitude +13.5 (comparable to Pluto), and orbits Neptune in a retrograde path once every 6 days, getting a maximum of 15” from the disk of the planet.

Nep Aug-Nov Triton aug 31 — The path of Neptune from late August through early November 2015. Inset: the position of Neptune’s moon Triton on the evening of August 31st: Image credit: Starry Night Education software

Uranus reaches opposition on October 11^th in the adjacent constellation Pisces. Keep an eye on Uranus, as it nears the bright +5.2 magnitude star Zeta Piscium towards the end on 2015. Shining at magnitude +5.7 with a 3.6 arc second disk, Uranus hovers just on the edge of naked eye visibility from a dark sky site.

Credit — Uranus, left of the eclipsed Moon last October. Image credit and copyright: A Nartist

It’ll be worth hunting for Uranus on the night of September 27^th/28^th, when it sits 15 degrees east of the eclipsed Moon. Uranus turned up in many images of last Fall’s total lunar eclipse. This will be the final total lunar eclipse of the current tetrad, and the Moon will occult Uranus the evening after for the South Atlantic. This is part of a series of 19 ongoing occultations of Uranus by the Moon worldwide, which started in August 2014, and end on December 20^th, 2015. After that, the Moon will move on and begin occulting Neptune next year in June through the end of 2017.

Occultation — The visibility footprint of the September 29th occultation of Uranus by the Moon. Image credit: Occult 4.0.

Uranus has 27 known moons, four of which (Oberon, Ariel, Umbriel and Titania) are visible in a large backyard telescope. See our extensive article on hunting the moons of the solar system for more info, and the JPL/PDS rings node for corkscrew finder charts.

Uranus aug-dec moons oct12 — The path of Uranus, from late August through early December 2015. Inset: the position of the moons of Uranus on the evening of October 12th. Image credit: Starry Night Education software

The two outermost worlds have a fascinating entwined history. William Herschel discovered Uranus on the night of March 13^th, 1781. We can be thankful that the proposed name ‘George’ after William’s benefactor King George the III didn’t stick. Herschel initially thought he’d discovered a comet, until he followed the slow motion of Uranus over several nights and realized that it had to be something large orbiting at a great distance from the Sun. Keep in mind, Uranus and Neptune both crept onto star charts unnoticed pre-1781. Galileo even famously sketched Neptune near Jupiter in 1612! Early astronomers simply considered the classical solar system out to Saturn as complete, end of story.

And the hunt was on. Astronomers soon realized that Uranus wasn’t staying put: something farther still from the Sun was tugging at its orbit. Mathematician Urbain Le Verrier predicted the position of the unseen planet, and on and on the night of September 23^rd, 1846, astronomers at the Berlin observatory spied Neptune.

In a way, those early 19^th century astronomers were lucky. Neptune and Uranus had just passed each other during a close encounter in 1821. Otherwise, Neptune might’ve remained hidden for several more decades. The synodic period of the two planets—that is, the time it takes the planets to return to opposition—differ by about 2-3 days. The very first documented conjunction of Neptune and Uranus occurred back in 1993, and won’t occur again until 2164. Heck, In 2010, Neptune completed its first orbit since discovery!

To date, only one mission, Voyager 2, has given us a close-up look at Uranus and Neptune during brief flybys. The final planetary encounter for Voyager 2 occurred in late August in 1989, when the spacecraft passed 4,800 kilometres (3,000 miles) above the north pole of Neptune.

All thoughts to ponder as you hunt for the outer ice giants. Sure, they’re tiny dots, but as with many nighttime treats, the ‘wow’ factor comes with just what you’re seeing, and the amazing story behind it.

August 24, 2015December 23, 2015 by David Dickinson

Astro-Challenge: Splitting 44 Boötis

44 Bootis from the Palomar Sky Survey. Image credit: The CDS/Aladin previewer

How good are your optics? Nothing can challenge the resolution of a large light bucket telescope, like attempting to split close double stars. This week, we’d like to highlight a curious triple star system that presents a supreme challenge over the next few years and will ‘keep on giving’ for decades to come.

The location of 44 Boötis in the constellation of the Herdsman. Image credit: Stellarium click image to enlarge

The star system in question is 44 Boötis, in the umlaut-adorned constellation of Boötes the herdsman. Boötes is still riding high to the west at dusk for northern hemisphere observers in late August, providing observers a chance to split the pair during prime-time viewing hours.

Sometimes also referred to as Iota Boötis, William Herschel first measured the angular separation of the pair in 1781, and F.G.W. Struve discovered the binary nature of 44 Boötis in 1832. Back then, the pair was headed towards a maximum apparent separation of 5 arc seconds in 1870. We call this point apastron. A fast forward to 2015 sees the situation reversed, as the pair currently sits about an arc second apart, and closing. 44 Boötis will pass a periastron of just 0.23” from the primary in 2020. Can you split the pair now? How ‘bout in 2016 onward? Can you recover the split, post 2020?

The physical parameters of the system are amazing. About 42 light years distant, 44 Boötis A is 1.05 times as massive as our Sun, and shines at magnitude +4.8. The B component is in a 210 year elliptical orbit with a semi-major axis of 49 AUs (for comparison, Pluto at aphelion is 49 AUs from the Sun), and is itself a curious contact spectroscopic binary about one magnitude fainter. Though you won’t be able to split the B-C pair with a backyard telescope, they betray their presence to professional instruments due to their intertwined spectra. 44 Boötis B and C have a combined mass of 1.5 times that of our Sun, and orbit each other once every 6.4 hours at a center-to-center distance of only 750,000 miles, or only 3 times the distance from Earth to the Moon:

That’s close enough that the pair shares a merging atmosphere. It’s a mystery as to just how these types of contact binary stars form, and it would be fascinating to see 44 Boötis up close. This fast spin along our line of sight also means that 44 Boötis B-C varies in brightness by about half a magnitude over a six hour span.

An artist’s conception of the B-C pair of the 44 Boötis system, using data from the Chandra X-ray observatory. Image credit: NASA/CXC/M.Weiss

Though the visual 44 Boötis A-B pair doesn’t quite have an orbital period that the average humanoid could expect to live through, beginning amateur astronomers can watch as the pair once again heads towards a wide an easy 5” split during apastron around 2080.

Collimation, or the near-perfect alignment of optics, is key to the splitting close binaries, and also serves as a good test of a telescope and the stability of the atmosphere. A well-collimated scope will display stars with sharp round Airy disks, looking like luminescent circular ripples in a pond. We call the lower boundary to splitting double stars the Dawes Limit, and on most nights, atmospheric seeing will limit this to about an arc second.

But there’s another method that you can use to ‘split’ doubles closer than an arc second, known as interferometry. This relies on observing the star by use of a filtering mask with two slits that vary in distance across the aperture of the scope. When the mask is rotated to the appropriate position angle and the slits are adjusted properly, the ‘fringes’ of the star snap into focus. A formula utilizing the slit separation can then calculate the separation of the close binary pair. This method works with stars that are A). Closer than 1” separation, and B). Vary by not more than a magnitude in brightness difference.

44 Boötis near periastron definitely qualifies. As of this writing, our ‘cardboard interferometer’ is still very much a work in progress. We could envision a more complex version of this rig mechanized, complete with video analysis. Hey, if nothing else, it really draws stares from fellow amateur astronomers…

We promise to delve into the exciting realm of backyard cardboard interferometry once we’ve worked all of the bugs out. In the meantime, be sure to regale us with your tales of tragedy and triumph observing 44 Boötis. Revisiting double stars can pose a life-long pursuit!

– Be sure to check out another double star challenge from Universe Today, with the hunt for Sirius B.

August 11, 2015December 23, 2015 by David Dickinson

A Thrift Store Find Yields an Astronomical Mystery

A good mystery is often where you find it. Photographer Meagan Abell recently made a discovery during a thrift store expedition that not only set the internet abuzz, but also contains an interesting astronomical dimension as well. This is an instance where observational astronomy may play a key role in pinning down a date, and we’d like to put this story before the Universe Today community for further insight and consideration.

Meagan first discovered the set of four medium format negatives at a thrift store on Hull Street in Richmond, Virginia. Beyond that, they have no provenance. Meagan was amazed at what see saw when she scanned in the negatives: the images of a woman walking into the surf have an ethereal beauty all their own. Obviously the work of a skilled photographer, the photos appear to date from the late 1940s or 1950s.

Meagan turned to social media for help, and cyber-sleuths responded in a big way. #FindTheGirlsOnTheNegatives became a viral hit, but thus far, who the women in the images are and the story behind them remains a mystery.

We do know one tantalizing bit of information: several Facebook users have pinned down the location as Dockweiler Beach, California near Los Angeles International Airport. Keen-eyed observers noted the similarity of the outline of the distant hills seen to the north in one of the images.

A few things caught our eye upon reading the mystery of the girls in the negatives this past weekend. One shot clearly shows the notch of the Sun just below the twilight horizon. A second, even more intriguing image shows a tiny sliver of Moon just to the subject’s upper left.

Could a date, or set of dates, be estimated based on these factors alone?

Let’s slip into astro-detective mode now. A few things are obvious right off the bat. First, the Moon is a waxing crescent, meaning the shots would have to be set in the evening. This also lends credence to the ocean being the Pacific, because the sunset is occurring over water. The similarity in cloud formations across all of the images seen also strongly suggests the photographer took all of the pictures on the same evening, during one session.

Can that crescent Moon tell us anything? It’s tiny and indistinct, but we have a few things to go on. The Moon looks to be a 5-6 day old waxing crescent about 30-40% illuminated. Not all waxing crescent Moons are created equal, as the ‘horns of the Moon’ can point in various directions based on the angle of the ecliptic to the local horizon at different times of the year.

The horns of the Moon appear to be oriented about 35 degrees from horizontal. Assuming the subject in the red dress is elevated slightly and about 20 feet from the observer, the Moon would be about 25-30 degrees above the horizon in the shot.

Now, Dockweiler Beach is located at latitude 33 degrees 55’ 20” north, longitude 118 degrees 26’ 3” west. The beach itself faces a perpendicular azimuth of 240 degrees out to sea, or roughly WSW.

Already, we can rule out winter and spring, because of the unfavorable angle of the dusk ecliptic. We want a time of year with A) a shallow southward ecliptic and B) a sunset roughly due west.

Turns out, late July through early October fit these ideal conditions for the location.

Can we narrow this even further? Well, here’s one possibility. Remember, this next step is what gumshoe PIs call a ‘hunch’…

The motion of the Moon is a wonderfully complicated affair. The path of the Moon is inclined about five degrees relative to the ecliptic, meaning that the Moon can ride anywhere from declination 28 degrees south, to 28 degrees north. From latitude 34 degrees north, this puts the mid-July ecliptic at about 33 degrees elevation across the meridian at sunset.

The nodal points where the path of the Moon crosses the ecliptic also precess slowly around the celestial sphere. This motion completes one revolution every 18.6 years, meaning that the Moon reaches those maximum declination values (sometimes referred to as a ‘long nights’ or the Major Lunar Standstill of the Moon) just under once every 19 years.

This occurred last in 2006, and will occur next in 2025. Incidentally, we’re at a shallow mid-point (known as a Minor Lunar Standstill) between the two dates this coming Fall.

A good fit? A comparison of the Moon in the image (left) with a simulated view in Stellarium from August 19th, 1950 (click to enlarge). Image credit: Dave Dickinson/Meagan Abell

This also puts the late summer 1^st quarter Moon as far south ‘in the weeds’ as possible. Extrapolating back in time, this sort of wide-ranging Moon occurred around 1949. Looking at the celestial scene in Stellarium, three dates nail the horn angle and elevation of the Moon seen in the photograph pretty closely around this time:

-August 11^th, 1948

-August 29^th, 1949

-August 19^th, 1950

Of course, this is just a hunch. Perhaps the subject was standing on a westward facing spit of rocks. Or maybe the photographer was closer or farther away than estimated. Or maybe the negative was inverted left to right along the way… that’s why I’d like to invite, you, the astute sky watcher, to weigh in.

And even if we pinned down the date, the mystery remains. Who are the girls in the negatives? What became of the photo shoot? And how did the negatives end up in a thrift store in Virginia?

Read another astronomical mystery sleuthed out by Dave Dickinson, with The Downing of Spirit ‘03: Did the Moon Play a Role?

Update: an sharp-eyed reader noticed that if you boost the contrast, you can see an additional ‘speck’ in the Moon image (see comment discussion below):

Update: Meagan responds: “The object along the horizon in the crescent Moon image is actually just a transparency defect.” A second image from the same strip does not show the white speck (arrowed above) near the horizon.

August 4, 2015December 23, 2015 by David Dickinson

The Dog Days and Sothic Cycles of August

The month of August is upon us once again, bringing with it humid days and sultry nights for North American observers.

You’ll often hear the first few weeks of August referred to as the Dog Days of Summer. Certainly, the oppressive midday heat may make you feel like lounging around in the shade like our canine companions. But did you know there is an astronomical tie-in for the Dog Days as well?

We’ve written extensively about the Dog Days of Summer previously, and how the 1460 year long Sothic Cycle of the ancient Egyptians became attributed to the Greek adoption of Sothis, and later in medieval times to the ‘Dog Star’ Sirius. Like the Blue Moon, say something wrong enough, long enough, and it successfully sticks and enters into meme-bank of popular culture.

Sirius (to the lower right) along with The Moon, Venus and Mercury and a forest fire taken on July 22, 2014. (Note- this was shot from the Coral Towers Observatory in the southern hemisphere). Image credit and copyright: Joseph Brimacombe

A water monopoly empire, the Egyptians livelihood rested on knowing when the annual flooding of the Nile was about to occur. To this end, they relied on the first seasonal spotting of Sirius at dawn. Sirius is the brightest star in the sky, and you can just pick out the flicker of Sirius in early August low to the southeast if you know exactly where to look for it.

Sundown over Cairo during the annual flooding of the Nile river. Image Credit: Travels through the Crimea, Turkey and Egypt 1825-28 (Public Domain). — Sundown over Cairo during the annual flooding of the Nile river. Image Credit: *Travels through the Crimea, Turkey and Egypt 1825-28* (Public Domain).

Sirius lies at a declination of just under 17 degrees south of the celestial equator. It’s interesting to note that in modern times, the annual flooding of the Nile (prior to the completion of the Aswan Dam in 1970) is commemorated as occurring right around August 15th. Why the discrepancy? Part of it is due to the 26,000 year wobbling of the Earth’s axis known as the Precession of the Equinoxes; also, the Sothic calendar had no intercalculary or embolismic (think leap days) to keep a Sothic year in sync with the sidereal year. The Sothic cycle from one average first sighting of Sirius to another is 365.25 days, and just 9 minutes and 8 seconds short of a sidereal year.

But that does add up over time. German historian Eduard Meyer first described the Sothic Cycle in 1904, and tablets mention its use as a calendar back to 2781 BC. And just over 3 Sothic periods later (note that 1460= 365.25 x 4, which is the number of Julian years equal to 1461 Sothic years, as the two cycles ‘sync up’), and the flooding of the Nile now no longer quite coincides with the first sighting of Sirius.

Such a simultaneous sighting with the sunrise is known in astronomy as a heliacal rising. Remember that atmospheric extinction plays a role sighting Sirius in the swampy air mass of the atmosphere low to the horizon, taking its usual brilliant luster of magnitude -1.46 down to a more than a full magnitude and diminishing its intensity over 2.5 times.

This year, we transposed the seasonal predicted ‘first sightings’ of Sirius versus latitude onto a map of North America:

Another factor that has skewed the date of first ‘Sirius-sign’ is the apparent motion of the star itself. At 8.6 light years distant, Sirius appears to move 1.3 arc seconds per year. That’s not much, but over the span of one Sothic cycle, that amounts up to 31.6’, just larger than the average diameter of a Full Moon.

Sirius has been the star of legends and lore as well, not the least of which is the curious case of the Dogon people of Mali and their supposed privileged knowledge of its white dwarf companion star. Alvan Graham Clark and his father discovered Sirius B in 1862 as they tested out their shiny new 18.5-inch refractor. And speaking of Sirius B, keep a telescopic eye on the Dog Star, as the best chances to spy Sirius B peeking out from the glare of its primary are coming right up around 2020.

Sirius image Credit — The dazzling visage of Sirius. Image credit: Dave Dickinson

Repeating the visual feat of spying Sirius B low in the dawn can give you an appreciation as to the astronomical skill of ancient cultures. They not only realized the first sighting of Sirius in the dawn skies coincided with the annual Nile flooding, but they identified the discrepancy between the Sothic and sidereal year, to boot. Not bad, using nothing but naked eye observations. Such ability must have almost seemed magical to the ancients, as if the stars had laid out a celestial edge for the Egyptians to exploit.

You can also exploit one method of teasing out Sirius from the dawn sky a bit early that wasn’t available to those Egyptian astronomer priests: using a pair of binoculars to sweep the skies. Can you nab Sirius with a telescope and track it up into the daytime skies? Sirius is just bright enough to see in the daytime against a clear blue sky with good transparency if you know exactly where to look for it.

Let the Dog Days of 2015 begin!

July 28, 2015December 23, 2015 by David Dickinson

Faces of the Solar System

Move over, Pluto... Disney already has dibs on Mercury as seen in this MESSENGER photo. Image credit: NASA/JHAPL/Carnegie institution of Washington

“Look, it has a tiny face on it!”

This sentiment was echoed ‘round the web recently, as an image of Pluto’s tiny moon Nix was released by the NASA New Horizons team. Sure, we’ve all been there. Lay back in a field on a lazy July summer’s day, and soon, you’ll see faces of all sorts in the puffy stratocumulus clouds holding the promise of afternoon showers.

Pluto's moon Nix as imaged by New Horizons from 590,000 kilometers distant. Image credit: NASA/JHUAPL/SWRI — Pluto’s moon Nix as imaged by New Horizons from 590,000 kilometers distant. Image credit: NASA/JHUAPL/SWRI

This predilection is so hard-wired into our brains, that often our facial recognition software sees faces where there are none. Certainly, seeing faces is a worthy survival strategy; not only is this aspect of cognition handy in recognizing the friendlies of our own tribe, but it’s also useful in the reading of facial expressions by giving us cues of the myriad ‘tells’ in the social poker game of life.

And yes, there’s a term for the illusion of seeing faces in the visual static: pareidolia. We deal lots with pareidolia in astronomy and skeptical circles. As NASA images of brave new worlds are released, an army of basement bloggers are pouring over them, seeing miniature bigfoots, flowers, and yes, lots of humanoid figures and faces. Two craters and the gash of a trench for a mouth will do.

Now that new images of Pluto and its entourage of moons are pouring in, neural circuits ‘cross the web are misfiring, seeing faces, half-buried alien skeletons and artifacts strewn across Pluto and Charon. Of course, most of these claims are simply hilarious and easily dismissed… no one, for example, thinks the Earth’s Moon is an artificial construct, though its distorted nearside visage has been gazing upon the drama of humanity for millions of years.

Do you see the 'Man in the Moon?' Image credit: Dave Dickinson — Do you see the ‘Man in the Moon?’ Image credit: Dave Dickinson

The psychology of seeing faces is such that a whole region of the occipital lobe of the brain known as the fusiform face area is dedicated to facial recognition. We each have a unique set of neurons that fire in patterns to recognize the faces of Donald Trump and Hillary Clinton, and other celebs (thanks, internet).

Damage this area at the base of the brain or mess with its circuitry, and a condition known as prosopagnosia, or face blindness can occur. Author Oliver Sacks and actor Brad Pitt are just a few famous personalities who suffer from this affliction.

The 'Snowman of Vesta,' as imaged by NASA's Dawn spacecraft. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA — The ‘Snowman of Vesta,’ as imaged by NASA’s Dawn spacecraft. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Conversely, ‘super-recognizers’ at the other end of the spectrum have a keen sense for facial identification that verges on a super-power. True story: my wife has just such a gift, and can immediately spot second-string actors and actresses in modern movies from flicks and television shows decades old.

It would be interesting to know if there’s a correlation between face blindness, super-recognition and seeing faces in the shadows and contrast on distant worlds… to our knowledge, no such study has been conducted. Do super-recognizers see faces in the shadowy ridges and craters of the solar system more or less than everyone else?

A well-known example was the infamous ‘Face on Mars.’ Imaged by the Viking 1 orbiter in 1976, this half in shadow image looked like a human face peering back up at us from the surface of the Red Planet from the Cydonia region.

Image credit: The 'Face on Mars': HiRISE vs Viking 1 (inset): Image credit: NASA/JPL — Image credit: The ‘Face on Mars’: HiRISE vs Viking 1 (inset): Image credit: NASA/JPL

But when is a face not a face?

Now, it’s not an entirely far-fetched idea that an alien entity visiting the solar system would place something (think the monolith on the Moon from Arthur C. Clarke’s 2001: A Space Odyssey) for us to find. The idea is simple: place such an artifact so that it not only sticks out like a sore thumb, but also so it isn’t noticed until we become a space-faring society. Such a serious claim would, however, to paraphrase Carl Sagan, demand serious and rigorous evidence.

But instead of ‘Big NASA’ moving to cover up the ‘face,’ they did indeed re-image the region with both the Mars Reconnaissance Orbiter and Mars Global Surveyor at a much higher resolution. Though the 1.5 kilometer feature is still intriguing from a geological perspective… it’s now highly un-facelike in appearance.

A 'face' or... more fun with 'scifi spacecraft pareidolia. Image credit: NASA/JPL/Paramount Pictures — A ‘face’ or… more fun with ‘scifi spacecraft pareidolia.’ Image credit: NASA/JPL/Paramount Pictures

Of course, it won’t stop the deniers from claiming it was all a big cover-up… but if that were the case, why release such images and make them freely available online? We’ve worked in the military before, and can attest that NASA is actually the most transparent of government agencies.

We also know the click bait claims of all sorts of alleged sightings will continue to crop up across the web, with cries of ‘Wake up, Sheeople!’ (usually in all caps) as a brave band of science-writing volunteers continue to smack down astro-pareidolia on a pro bono basis in battle of darkness and light which will probably never end.

What examples of astro-pareidolia have you come across in your exploits?

July 27, 2015December 23, 2015 by David Dickinson

Blues for the Second Full Moon of July

An artificially created 'Blue Moon,' using the white balance settings on the camera. Image credit and copyright: John Chumack

Brace yourselves for Blue Moon madness. The month of July 2015 hosts two Full Moons: One on July 2^nd and another coming right up this week on Friday, July 31^st 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 31^st, 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?

The ghostly glow of the gibbous moon in Jean-Francois Millet's The Sheepfold. Image Credit: Public Domain — The ghostly glow of the gibbous moon in Jean-Francois Millet’s The Sheepfold. Image Credit: Public Domain

We’ve also laid out the occurrences for both types of Blue Moons for the remainder of the decade, as well as its New Moon cousin and internet meme to be, the Black Moon.

Untitled — The rising waxing gibbous Moon on the night of September 23rd, 1950. Image credit: Stellarium

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 23^rd, 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 29^th, September 28^th, and October 27^th. 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.

A 'mock Blue Moon...' — A ‘mock Blue Moon…’ induced by use of a military flashlight filter. Image credit: Dave Dickinson

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.

July 21, 2015December 23, 2015 by David Dickinson

Moonspotting-A Guide to Observing the Moons of the Solar System

Like splitting double stars, hunting for the faint lesser known moons of the solar system offers a supreme challenge for the visual observer.

Sure, you’ve seen the Jovian moons do their dance, and Titan is old friend for many a star party patron as they check out the rings of Saturn… but have you ever spotted Triton or Amalthea?

Welcome to the challenging world of moon-spotting. Discovering these moons for yourself can be an unforgettable thrill.

One of the key challenges in spotting many of the fainter moons is the fact that they lie so close inside the glare of their respective host planet. For example, +11^th magnitude Phobos wouldn’t be all that tough on its own, were it not for the fact that it always lies close to dazzling Mars. 10 magnitudes equals a 10,000-fold change in brightness, and the fact that most of these moons are swapped out is what makes them so tough to see. This is also why many of them weren’t discovered until later on.

But don’t despair. One thing you can use that’s relatively easy to construct is an occulting bar eyepiece. This will allow you to hide the dazzle of the planet behind the bar while scanning the suspect area to the side for the faint moon. Large aperture, steady skies, and well collimated optics are a must as well, and don’t be afraid to crank up the magnification in your quest. We mentioned using such a technique previously as a method to tease out the white dwarf star Sirius b in the years to come.

What follows is a comprehensive list of the well known ‘easy ones,’ along with some challenges.

We included a handy drill down of magnitudes, orbital periods and maximum separations for the moons of each planet right around opposition. For the more difficult moons, we also noted the circumstances of their discovery, just to give the reader some idea what it takes to see these fleeting worlds. Remember though, many of those old scopes used speculum metal mirrors which were vastly inferior to commercial optics available today. You may have a large Dobsonian scope available that rivals these scopes of yore!

Mars- The two tiny moons of Mars are a challenge, as it’s only possible to nab them visually near opposition, which occurs about once every 26 months. Mars next reaches opposition on May 22^nd, 2016.

Phobos:

Magnitude: +11.3

Orbital period: 7 hours 39 minutes

Maximum separation: 16”

Deimos:

Magnitude: +12.3

Orbital period: 1 day 6 hours and 20 minutes

Maximum separation: 54”

The moons of Mars were discovered by American astronomer Asaph Hall during the favorable 1877 opposition of Mars using the 26-inch refracting telescope at the U.S. Naval Observatory.

Jupiter- Though the largest planet in our solar system also has the largest number of moons at 67, only the four bright Galilean moons are easily observable, although owners of large light buckets might just be able to tease out another two. Jupiter next reaches opposition March 8^th, 2016.

Ganymede:

Magnitude: +4.6

Orbital period: 7.2 days

Maximum separation: 5’

Callisto

Magnitude: +5.7

Orbital period: 16.7 days

Maximum separation: 9’

Magnitude: +5.0

Orbital period: 1.8 days

Maximum separation: 1’ 50”

Europa

Magnitude: +5.3

Orbital period: 3.6 days

Maximum separation: 3’

Amalthea

Magnitude: +14.3

Orbital period: 11 hours 57 minutes

Maximum separation: 33”

Himalia

Magnitude: +15

Orbital period: 250.2 days

Maximum separation: 52’

Note that Amalthea was the first of Jupiter’s moons discovered after the four Galilean moons. Amalthea was first spotted in 1892 by E. E. Barnard using the 36” refractor at the Lick Observatory. Himalia was also discovered at Lick by Charles Dillon Perrine in 1904.

Titan and Rhea imaged via Iphone and a Celestron NexStar 8SE telescope. Image credit: Andrew Symes (@failedprotostar)

Saturn- With a total number of moons at 62, six moons of Saturn are easily observable with a backyard telescope, though keen-eyed observers might just be able to tease out another two:

(Note: the listed separation from the moons of Saturn is from the limb of the disk, not the rings).

Titan

Magnitude: +8.5

Orbital period: 16 days

Maximum separation: 3’

Rhea

Magnitude: +10.0

Orbital period: 4.5 days

Maximum separation: 1’ 12”

Iapetus

Magnitude: (variable) +10.2 to +11.9

Orbital period: 79 days

Maximum separation: 9’

Enceladus

Magnitude: +12

Orbital period: 1.4 days

Maximum separation: 27″

Dione

Magnitude: +10.4

Orbital period: 2.7 days

Maximum separation: 46”

Tethys

Magnitude: +10.2

Orbital period: 1.9 days

Maximum separation: 35”

Mimas

Magnitude: +12.9

Orbital period: 0.9 days

Maximum separation: 18”

Hyperion

Magnitude: +14.1

Orbital period: 21.3 days

Maximum separation: 3’ 30”

Phoebe

Magnitude: +16.6

Orbital period: 541 days

Maximum separation: 27’

Hyperion was discovered by William Bond using the Harvard observatory’s 15” refractor in 1848, and Phoebe was the first moon discovered photographically by William Pickering in 1899.

Uranus- All of the moons of the ice giants are tough. Though Uranus has a total of 27 moons, only five of them might be spied using a backyard scope. Uranus next reaches opposition on October 12^th, 2015.

Titania

Magnitude: +13.9

Orbital period:

Maximum separation: 28”

Oberon

Magnitude: +14.1

Orbital period: 8.7 days

Maximum separation: 40”

Umbriel

Magnitude: +15

Orbital period: 4.1 days

Maximum separation: 15”

Ariel

Magnitude: +14.3

Orbital period: 2.5 days

Maximum separation: 13”

Miranda

Magnitude: +16.5

Orbital period: 1.4 days

Maximum separation: 9”

The first two moons of Uranus, Titania and Oberon, were discovered by William Herschel in 1787 using his 49.5” telescope, the largest of its day.

Neptune- With a total number of moons numbering 14, two are within reach of the skilled amateur observer. Opposition for Neptune is coming right up on September 1^st, 2015.

Triton

Magnitude: +13.5

Orbital period: 5.9 days

Maximum separation: 15”

Nereid

Magnitude: +18.7

Orbital period: 0.3 days

Maximum separation: 6’40”

Triton was discovered by William Lassell using a 24” reflector in 1846, just 17 days after the discovery of Neptune itself. Nereid wasn’t found until 1949 by Gerard Kuiper.

Pluto-Yes… it is possible to spy Charon from Earth… as amateur astronomers proved in 2008.

Charon

Magnitude: +16

Orbital period: 6.4 days

Maximum separation: 0.8”

In order to cross off some of the more difficult targets on the list, you’ll need to know exactly when these moons are at their greatest elongation. Sky and Telescope has some great apps in the case of Jupiter and Saturn… the PDS Rings node can also generate corkscrew charts of lesser known moons, and Starry Night has ‘em as well. In addition, we tend to publish cork screw charts for moons right around respective oppositions, and our ephemeris for Charon elongations though July 2015 is still active.

Good luck in crossing off some of these faint moons from your astronomical life list!