Observing Archives

June 3, 2015December 23, 2015 by David Dickinson

Solved: The Riddle of the Nova of 1670

This chart of the position of a nova (marked in red) that appeared in the year 1670 recorded by the astronomer Hevelius and was published by the Royal Society in England in their journal Philosophical Transactions. Image credit: The Royal Society

It is a 17^th century astronomical enigma that has persisted right up until modern times.

On June 20, 1670, a new star appeared in the evening sky that gave 17^th century astronomers pause. Eventually peaking out at +3^rdmagnitude, the ruddy new star in the modern day constellation of Vulpecula the Fox was visible for almost two years before vanishing from sight.

The exact nature of Nova Vulpeculae 1670 has always remained a mystery. The event has often been described as a classic nova… but if it was indeed a garden variety recurrent nova in our own Milky Way galaxy, then why haven’t we seen further outbursts? And why did it stay so bright, for so long?

Now, recent findings from the European Southern Observatory announced in the journal Nature this past March reveal something even more profound: the Nova of 1670 may have actually been the result of a rare stellar collision.

The remnant of the nova of 1670 seen with modern instruments and created from a combination of visible-light images from the Gemini telescope (blue), a submillimetre map showing the dust from the SMA (yellow) and finally a map of the molecular emission from APEX and the SMA (red). Image credit: ESO/T. Kaminski

“For many years, this object was thought to be a nova,” said ESO researcher Tomasz Kaminski of the Max Planck Institute for Radio Astronomy in Bonn Germany in a recent press release. “But the more it was studied, the less it looked like an ordinary nova—or indeed any other kind of exploding star.”

A typical nova occurs when material being siphoned off a companion star onto a white dwarf star during a process known as accretion builds up to a point where a runaway fusion reaction occurs.

ESO researchers used an instrument known as the Atacama Pathfinder EXperiment telescope (APEX) based on the high Chajnantor plateau in Chile to probe the remnant nebula from the 1670 event at submillimeter wavelengths. They found that the mass and isotopic composition of the resulting nebula was very uncharacteristic of a standard nova event.

So what was it?

A best fit model for the 1670 event is a rare stellar merger, with two main sequence stars smashing together and exploding in a grand head on collision, leaving the resulting nebula we see today. This event also resulted in a newly recognized category of star known as a “red transient” or luminous red nova.

Universe Today caught up with Mr. Kaminski recently on the subject of red transients and the amazing find:

“In our galaxy we are quite confident that four other objects were observed in outburst owing to a stellar merger: V838 Mon (famous for its spectacular light echo, eruption 2002), V4332 Sgr (eruption 1994), V1309 Sco (observed as an eclipsing binary before its outburst in 2008), OGLE-2002-BLG-360 (recent, but most similar to CK Vul eruption, 2002).Red transients are bright enough to be observed in nearby galaxies. Among them are M31 RV (first recognized “red variable”, eruption 1989), M85 OT2006 (eruption 2006), NGC300 OT2008, etc. Very recently, a few months ago, another one went off in the Andromeda Galaxy. With the increasing number of sky surveys we surely will discover many more.”

Though astronomers such as Voituret Anthelme, Johannes Hevelius and Giovanni Cassini all noted the 1670 nova, the nebula and suspected progenitor star wasn’t successfully recovered until 1981. Often cited as the oldest and faintest observation of a nova, Hevelius referred to the 1670 apparition as ‘nova sub capite Cygni,’ or a new star located below the head of the Swan near the star Albireo the constellation of Cygnus. Astronomers of the day also noted the crimson color of the new star, also fitting with the modern red transient hypothesis of two main sequence stars merging.

This map includes most of the stars that can be seen on a dark clear night with the naked eye. It shows the small constellation of Vulpecula (The Fox), which lies close to the more prominent constellation of Cygnus (The Swan) in the northern Milky Way. The location of the exploding star Nova Vul 1670 is marked with a red circle. — This chart shows the small constellation of Vulpecula (The Fox), and the location of the exploding star Nova Vul 1670 (red circle). Image credit: ESO/IAU/Sky & Telescope

“We observed CK Vul with the hope to find some submillimeter emission, but were completely surprised by how intense the emission was and how abundant in molecules the gas surrounding CK Vul is,” Kaminski told Universe Today. “Also, we have ongoing observational programs to search for objects similar to CK Vul.”

Follow up observations of the region were also carried out by the Submillimeter Array (SMA) and the Effelsberg radio telescope in Germany. The Nova of 1670 occurred about 1,800 light years distant along the galactic plane in the Orion-Cygnus arm of our Milky Way galaxy, of which the Sun and our solar system is a member. We actually had a naked eye classical nova just last year in roughly the same direction, which was visible in the adjacent constellation of Delphinus the Dolphin.

Of course, these garden variety novae are in a distinctly different class of events from supernovae, the likes of which have not been seen in our galaxy with the unaided eye in modern times since Kepler’s supernova in 1604.

The Atacama Pathfinder Experiment (APEX) telescope on the hunt. Image credit: ESO/ Babak Tafreshi

How often do stars collide? While rogue collisions of passing stars are extremely rare—remember, space is mostly nothing—the odds go up for closely orbiting binary pairs. What would really be amazing is to witness a modern day nearby red transient in the act of formation, though for now, we’ll have to console ourselves with studying the aftermath of the 1670 event as the next best thing.

“Recent estimates give one (merger) event per 2 years in the Milky Way galaxy,” Kaminski told Universe Today. “But we currently know so little about violent merger events that this number is very uncertain.”

Previously cited as a recurrent nova, the story of the 1670 event is a wonderful example of how new methods, combined with old observations, can be utilized to solve some of the lingering mysteries of modern astronomy.

May 31, 2015December 23, 2015 by Bob King

Allergies? Must Be Pollen Corona Season Again

A multi-ringed, oval shaped corona around the Sun on May 30, 2015 seen from northern Minnesota. The white spots are aspen seeds better known as "cotton fluff". Credit: Bob King

Don’t be surprised if you look up in the Sun’s direction and squint with itchy, watery eyes. You might be staring into billows of tree pollen wafting through your town. It’s certainly been happening where I live.

When conditions are right, billions of microscopic pollen grains consort to create small, oval-shaped rings around a bright Moon during the peak of the spring and early summer allergy season. With the Full Moon coming up this week, there’s no better time to watch for them.

Pollen grains from a variety of different common plants including sunflower, morning glory, prairie hollyhock and evening primrose. Credit: Dartmouth Electron Microscope Facility, Dartmouth College — Pollen grains from a variety of different common plants including sunflower, morning glory, prairie hollyhock and evening primrose magnified 500x and colorized. The green, bean-shaped grain at lower left is 0.05 mm across. Credit: Dartmouth Electron Microscope Facility

Because they’re often lost in the glare of the Sun or Moon, the key to finding one is to hide the solar or lunar disk behind a thick tree branch, roof or my favorite, the power pole. Look for a telltale oval glow, sometimes tinted with rainbow colors, right up next to the Moon or Sun’s edge. Common halos, those that form when light is refracted by ice crystals, span 44° compared to pollen coronas, which measure just a few degrees in diameter.

To see or photograph coronas, you need plenty of light. The Sun’s ideal, but so is the Moon around full. Fortunately, that happens on June 2, neatly fitting into the sneezing season. Last night, the same grains — most likely pine tree pollen — also stoked a lunar corona. Once my eyes were dark adapted and the Moon hidden by an arboreal occulting instrument (tree branch), it was easy to see.

A lunar pollen corona on May 30, 2015. The Moon was hidden by a utility pole. Like the solar version, this one is elongated too. The shape is caused by pollen grains' elongated shape and the fact that they tend to orient themselves as they drift in the wind. Credit: Bob King — A lunar pollen corona on May 30, 2015. The Moon was hidden by a utility pole. Like the solar version, this one was also oval and measured about 3.5° across. The shape is caused by elongated pollen grains fact that orient themselves as they drift in the wind. Credit: Bob King

One of things you’ll notice right away about these biological bullseyes is that they’re not circular. Pollen coronas are oval because the pollen particles are elongated rather than spherical like water droplets. When light from the moon or sun strikes pollen, the minute grains diffract the light into a series of closely-spaced colored rings. I’ve read that pine and birch produce the best coronas, but spruce, alder and and others will work, too.

And here’s another amazing thing about these coronas. You don’t need a transparent medium to produce them. No ice, no water. All that’s necessary are very small, similarly-shaped objects. Light waves are scattered directly off their surfaces; the waves interfere with one another to create a diffraction pattern of colored rings.

A lunar pollen corona photographed on June 22, 2008 displays “bumps” or extensions at approximately 90° angles around its periphery. Credit: Bob King

Pollen coronas tend to become more elongated when the Sun or Moon is closer to the horizon, so look be on the lookout during those times for more extreme shapes. For some reason I’ve yet to discover, pollen disks sometimes exhibit “bumps” or extensions at their tops, bottoms and sides.

So many of us suffer from allergies, perhaps the glowing presence of what’s causing all the inflammation will serve as partial compensation for our misery.

May 26, 2015December 23, 2015 by David Dickinson

Getting Ready For International Space Station Observing Season

The summer season means long days and short nights, as observers in the northern hemisphere must stay up later each evening waiting for darkness to fall. It also means that the best season to spot that orbital outpost of humanity—the International Space Station—is almost upon us. Get set for multiple passes a night for observers based in mid- to high- northern latitudes, starting this week.

This phenomenon is the result of the station’s steep 52 degree inclination orbit. This means that near either solstice, the ISS spends a span of several days in permanent illumination. Multiple sightings favor the southern hemisphere around the December solstice and the northern hemisphere right around the upcoming June solstice.

Here’s a rundown of the ‘ISS all night’ season for 2015. The Sun rises on the ISS after a brief three minute orbital night on May 30^th, 2015 at 16:43 UT, and doesn’t set again until five days later on June 4^th at 4:57 UT over the central US. The ISS full illumination season comes a bit early this year—a few weeks before the June 21st northward solstice—and the next prospect at the end of July sees the Sun angle juuust shy of actually creating a second summer season.

NASA engineers refer to this period as high solar beta angle season. For a satellite in low Earth orbit, the beta angle describes the angle between its orbital plane and the relative direction of the Sun. Beta angle governs the satellite’s length of time in darkness and daylight. In the shuttle era, the Space Shuttle could not approach the ISS during these ‘beta cutout’ times, and the station generally goes into ‘rotisserie mode,’ as the ISS is rotated and its solar panels feathered to create alternating regions of artificial darkness in an effort to combat the continuous heating.

Why the 52 degree inclination orbit for the station? This allows the ISS to be accessible from launch sites worldwide in the spirit of international cooperation exemplified by the ISS. The station can and has been reached by cargo and human crews launching from Cape Canaveral and the Kennedy Space Center in Florida, the Baikonur Cosmodrome, the Tanegashima space port in Japan, and Kourou space center in French Guiana.

Our friend @OzoneVibe on Twitter suggested to us a few years back that a one night marathon session of ISS sightings be known as a FISSION, which stands for Four/Five ISS sightings In One Night. The prospective latitudes to carry out this feat run from 45 to 55 degrees north, which corresponds with northern Europe, the United Kingdom, and the region just north and south of the U.S./Canadian border.

At 72.8 by 108.5 metres in size and orbiting the Earth once every 92 minutes at an average 400 kilometres in altitude, the ISS is the brightest object in low Earth orbit, and reaches magnitude -2 in brightness—not quite as bright as Venus at maximum brightness—on a good overhead pass. Depending on the approach angle, I can just make out a bit of detail when the ISS is near the zenith, looking like either a box, a close double star, or a tiny Star Wars TIE fighter through binoculars. Numerous apps and platforms exist to predict ISS passes based on location, though our favorite is still the venerable Heavens-Above. It’s strange to think, we were using Heavens-Above to chase Mir back in the late 1990s!

There’s another interesting challenge, which, to our knowledge, has never been captured as we near high beta angle season for the ISS: catching an ‘ISS wink out,’ or that brief sunset followed by sunrise a few minutes later on the same pass. It’s worth noting that the central United States may see just such an event during an early morning pass on June 4^th… will you be the first to witness it?

Photographing the ISS is as easy as setting a DSLR on a tripod with a wide field of view lens, and doing a simple time exposure as it drifts by. Be sure to manually set the focus before the pass… Venus is currently well placed as a ‘mock ISS’ to get a fix on beforehand.

And amateur observers can even capture detail on the ISS, though this requires a camera running video coupled to a telescope. High precession tracking is desirable, though not mandatory: we’ve actually got descent results manually aiming a scope at the ISS with video running. The ISS appears in post production, occasionally skipping through the field of view.

PhD student Bob Lansdorp has made some great videos of the ISS with a similar rig.

Another unique method is to know when the ISS will transit the Sun, Moon or near a bright planet or star, aim your rig at the right spot, and let the station come to you. A good site to tailor alerts for such occurrences is CALSky.

After high beta angle season, missions to and from the ISS will resume. This includes the return of ISS crewmembers Shkaplerov, Christoforetti and Virts on June 7^th, followed by a Soyuz launch with Kononeko, Yui, and Lindgren on July 24^th. Also on tap is SpaceX’s Dragon capsule on CRS-7 launching on June 26^th, the return to flight for Progress on July 3^rd, and a HTV-5 launch for JAXA on August 17^th. These can also provide interesting views for ground observers as well, as these spacecraft follow the ISS in its orbit on approach like tiny fainter ‘stars.’

A busy season indeed. Don’t miss a chance to see the ISS coming to a sky near you, and watch as humans work together aboard this orbiting science platform in space.

May 20, 2015December 23, 2015 by David Dickinson

Hunting LightSail in Orbit

The hunt is on in the satellite tracking community, as the U.S. Air Force’s super-secret X-37B space plane rocketed into orbit today atop an Atlas V rocket out of Cape Canaveral. This marks the start of OTV-4, the X-37B’s fourth trip into low Earth orbit. And though NORAD won’t be publishing the orbital elements for the mission, it is sure to provide an interesting hunt for backyard satellite sleuths on the ground.

Previous OTV missions were placed in a 40 to 43.5 degree inclination orbit, and the current NOTAMs cite a 61 degree azimuth angle for today’s launch out of the Cape which suggests a slightly shallower 39 degree orbit. Such variability speaks to the versatile nature of the second stage Centaur motor.

There’s also been word afoot that future X-37B missions may return to Earth at the Kennedy Space Center, just like the Space Shuttle. To date, the X-37B has only landed at Vandenberg Air Force Base in California.

But there’s also another high interest payload being released along with a flock of CubeSats aboard AFPSC-5: The Planetary Society’s Lightsail-1.

About the size of a loaf of bread and the result of a successful Kickstarter campaign, LightSail is set to demonstrate key technologies in low Earth orbit before the Planetary Society’s main solar sail demonstrator takes to space in 2016.

The idea of using solar wind pressure for space travel is an enticing one. A big plus is the fact that unlike chemical propulsion, a solar sail does not need to contend with hauling the mass of its own fuel. The idea of using a solar sail plus a focused laser to propel an interstellar spacecraft has long been a staple of science fiction. But light-sailing technology has had a troubled history—the Planetary Society lost its Cosmos-1 mission launched from a Russian submarine in 2001. JAXA has fared better with its Venus-bound IKAROS, also equipped with a solar sail. To date, the IKAROS solar sail is the largest that has been deployed, at 20-metres on the diagonal.

Another use for space sail technology is the commanded reentry of spacecraft at the end of their mission life, as demonstrated by NanoSail-D2 in 2011.

Prospects of seeing LightSail may well be similar to what we had hunting for NanoSail-D2. Unfolded, LightSail will be 32 square meters in size, or about 5.6 meters on a side. NanoSail-D2 measured 3.1 meters on a side, and the reflective panels on the Iridium satellites which produce brilliant Iridium flares exceeding Venus in brightness measure about the size of a large rectangular door at 1 x 3 meters. Even the Hubble Space Telescope can flare on occasion as seen from the ground if one of its massive solar arrays catches the Sun just right.

The 39 degree orbital inclination angle will also limit visible passes to from about 45 degrees north to 45 degrees south latitude.

Hunting down X-37B and LightSail will push ground observing skills to the max. Like NanoSail-D2, LightSail probably won’t be visible to the naked eye until it flares. What we like to do is note when a faint satellite is set to pass by a bright star, then sit back with our trusty 15x 45 image-stabilized binoculars and watch. We caught sight of the ‘tool bag’ lost during an ISS EVA in 2009 in this fashion. There it was, drifting past Spica as a +7^th magnitude ‘star’. The key to this method is an accurate prediction—Heavens-Above now overlays orbital satellite passes on all-sky charts—and an accurate time source. We prefer to have WWV radio running in the background, as it’ll call out the time signal so we don’t have to take our eyes off the sky.

Veteran satellite watcher Ted Molczan recently discussed the prospects for spotting LightSail once it’s deployed. “By then, the orbit will be visible from the northern hemisphere during the middle of the night. The southern hemisphere may have marginal evening passes. Note that the high area to mass ratio with the sail deployed, combined with the low perigee height, is expected to result in decay as soon as a couple days after deployment.”

Read a further discussion concerning OTV-4 and associated payloads by Mr. Molczan on the See-Sat message board here.

The Planetary Society’s Jason Davis confirmed for Universe Today that LightSail will deploy 28 days after launch. But we may only have a slim two day observation window for LightSail between deployment and reentry.

A deployment of LightSail 28 days after launch would put it in the June 16^th timeframe.

“That’s the nominal mission time, yes,” Davis told Universe Today. “Our orbital models predict 2-10 days. For our 2016 flight, the mission will last at least four months.”

The Planetary Society plans to have a live ‘mission control center’ to track LightSail after P-POD deployment, complete with a Google Map showing pass predictions.

Satellite spotting can be a fun and addictive pastime, where part of the fun is sleuthing out what you’re seeing. Hey, some relics of space history such as the early Vanguards, Telstars, and Canada’s first satellite Alouette-1 are still up there! Nabbing these photographically are as simple as plopping your DSLR on a tripod, setting the focus and doing a time exposure as the satellite passes by.

Here’s to smooth solar sailing and clear skies as we embark on our quest to track down the X-37B and LightSail-1 in orbit.

-Follow us as @Astroguyz on Twitter, as we’ll be providing further info on orbits and visibility passes as they are made public.

May 13, 2015December 23, 2015 by David Dickinson

Review: Annals of the Deep Sky by Jeff Kanipe & Dennis Webb

Volumes 1 and 2 on sale now. Image credit: Willmann-Bell, Inc

Any lover of the night sky knows the value of a good star atlas and an astronomical handbook to guide your exploration of the universe. And while it’s true that more information exists out there than ever before online, much of it is intended for a general armchair astronomical audience, or is scattered about the web in disparate places…

But an exciting new series promises to be an essential must for deep sky observers. Annals of the Deep Sky: A Survey of Galactic and Extragalactic Objects by Jeff Kanipe and Dennis Webb is a through rundown of the night sky constellation-by-constellation which is aimed at the advanced observer. Mr. Kanipe is a science writer with 35 years experience, and Mr. Webb is a NASA engineer and observer with more than 25 years of experience exploring the night sky. If the names are familiar to deep sky fans, it might be because they also teamed up to produce the Arp Atlas of Peculiar Galaxies: A Chronicle and Observer’s Guide in 2006. Volumes 1 and 2 covering constellations in alphabetical order from Andromeda to Caelum are out now from Willmann-Bell, Inc., and the projected 12 volume set will cover all 88 constellations when completed. Volume 3 is due out in early 2016.

Messier 31 deconstructed by the Annals of the Deep Sky. Image credit: Willman-Bell, Inc — Messier 31 deconstructed by the *Annals of the Deep Sky*. Image credit: NASA/Willmann-Bell, Inc

Annals promises to join the ranks of some of the classic sky guides. Observers from the pre-digital era will recall the paucity of good observing resources available just a few decades ago. Growing up in rural northern Maine, even getting our hands on Sky and Telescope or Astronomy magazine was a daunting challenge, and we often gleaned knowledge of the astronomical goings on for the year from the tables of the Farmer’s Almanac. I remember hearing of the close 0.0312 AU passage past the Earth of Comet IRAS-Araki-Alcock in 1983, days after it had passed by! Contrast this with today, as message boards and Twitter alert us to new discoveries, sometimes within minutes.

Over the years, Ottewell’s yearly Astronomical Calendar has become a crucial resource as well.

Annals of the Deep Sky promises to be this generation’s answer to Burnham’s Celestial Handbook. You have to be of a certain age to remember Burnham’s, but that landmark three volume guide is one of the few hard copy resources that still resides on our desk well into the digital era. And Burnham’s has survived despite its use of now outdated 1950.0 stellar coordinates… that’s the kind of legendary staying power it has had in the amateur astronomy community!

A monument to Burnham's Celestial Handbook at the Lowell observatory in Flagstaff, Arizona. Image credit: David Dickinson — A monument to *Burnham’s Celestial Handbook* at the Lowell observatory in Flagstaff, Arizona. Image credit: David Dickinson

Annals of the Deep Sky begins with an outline of how to use the books, and a summary of basic observational astronomy and astrophysics. Like Burnham’s, Annals presents the field of observational astronomy beyond the solar system. But unlike Burnham’s—which was mainly text—the true magic of Annals lies in its extensive use of maps, diagrams and charts, all meant for the serious visual and photographic observer, both in planning observation runs and in the field. These also include some innovative ‘3-D’ style views through the constellations themselves as seen from our Earthly perspective. These views take the observer out through the plane of our galaxy and beyond as we peer out into the universe.

Annals of the Deep Sky also incorporates the latest discoveries and our understanding of the universe, as well as how our knowledge of astronomy and astrophysics got to where it is today. Annals not only provides the visual observer with handy field of view overlays for classic objects such as the Andromeda Galaxy (M31), but it also provides charts depicting camera sensor versus focal length and field of view for DLSR photography of key objects. To our knowledge, no other such resource for this specialized level of information exists for astrophotographers. We also enjoyed the graphic depictions of visual and spectroscopic binary star orbits, another tough item to dig up in research, even with today’s modern planetarium programs.

Representative views of visual (top) and spectroscopic binary orbits. Image credit: Willmann-Bell, Inc

The inclusion of history and astronomical lore is also a great touch that really makes the resource ‘pop’ in a vein similar to Burnham’s. This lends a fascinating dimension of astronomical history to the Annals that suits to a casual ‘shotgun’ reading style. Like Burnham’s, I can see discovering something new from a random opening of the Annals for years to come. A fine example is the lingering mystery of the Nova of 1860 in Volume 2 observed by Joseph Baxendell near Arcturus, a fascinating tale we’d never heard of.

We only wish that this awesome resource was also available in digital format so that we could carry this essential reference with us out in the field… we could easily envision cross-referencing information from a laptop planetarium program such as Starry Night or Stellarium at the eyepiece, with Annals of the Deep Sky cued up on the Kindle.

So grab that ‘Dobsonian light bucket’ and the first two volumes of Annals of the Deep Sky. This series promises to be an anticipated gem for many years to come. And hey, you can tell the next generation of hipster backyard observers that you remember what it was like before we had Annals of the Deep Sky to consult!

May 12, 2015December 23, 2015 by David Dickinson

A Guide to Saturn Through Opposition 2015

Getting closer... Saturn as seen on March 25th, 2015. Image credit: Efrain Morales

The month of May generally means the end of star party season here in Florida, as schools let out in early June, and humid days make for thunderstorm-laden nights. This also meant that we weren’t about to miss the past rare clear weekend at Starkey Park. Jupiter and Venus rode high in the sky, and even fleeting Mercury and a fine pass of the Hubble Space Telescope over central Florida put in an appearance.

But the ‘star’ of the show was the planet Saturn as it appeared at nightfall low to the southeast. Currently rising about 9:00 PM local, Saturn is joining the evening skies as it approaches opposition next week.

This also means we’ve got every naked eye planet set for prime time evening viewing this week with the exception of Mars, which reaches solar conjunction on June 14, 2015. Mercury will be the first world to break this streak, as it descends into the twilight glare by mid-May.

The apparent path of Saturn from May to November 2015. Image credit: Starry Night Education software

Saturn reaches opposition for 2015 on May 23^rd at 1:00 Universal Time (UT), which equates to 9:00 PM EDT the evening prior on May 22 at nearly 9 astronomical units (AU) distant. Oppositions of Saturn are getting slightly more distant to the tune of 10 million kilometers in 2015 versus last year as Saturn heads towards aphelion in 2018. Saturn crosses eastward from the astronomical constellation of Scorpius in the first week of May, and spends most of the remainder of 2015 in Libra before looping back into the Scorpion in mid-October. The first of June finds Saturn just over a degree southward of the +4th magnitude star Theta Librae. Saturn takes nearly 30 Earth years to complete one orbit, meaning that it was right around the same position in the sky in 1985, and will appear so again in 2045. Relatively speedy Jupiter also overtakes Saturn as seen from the Earth about once every 20 years, as it last did on 2000 and is set to do so again in 2020.

And though series of occultations of Saturn by the Moon wrapped up in 2014 and won’t resume again until December 9, 2018, there’s also a good chance to spy Saturn two degrees away from the daytime Moon with binoculars on June 1st just 24 hours prior to Full:

Looking east on the evening of June 1st just before sunset. Image credit: Stellarium

The tilt of the rings of Saturn is also slowly widening from our Earthbound perspective. At opposition, Saturn’s rings subtend 43” across, and the ochre disk of Saturn itself spans 19”. Incidentally, on a good pass, the International Station has a visual span roughly equivalent to Saturn plus rings. In 2015, the rings are tilted 24 degrees wide and headed for a maximum approaching 27 degrees in 2017. The rings appeared edge on in 2009 and will do so again in 2025.

Getting wider... our evolving view of Saturn's rings. Image credit and copyright: Andrew Symes — Getting wider… our evolving view of Saturn’s rings. Image credit and copyright: Andrew Symes

Also, keep an eye out for the Seeliger effect. Also sometimes referred to as the ‘opposition surge,’ this is a retroreflector-style effect that causes an outer planet to brighten up substantially on the days approaching opposition. In the case of Saturn and its rings, this effect can be especially dramatic. Not only is the disk of Saturn and the billions of icy snowballs casting shadows nearly straight back as seen from our vantage point near opposition, but a phenomenon known as coherent backscatter serves to increase the collective brightness of Saturn as well. You see the same effect at work as you drive down the Interstate at night, and highway signs and retroreflector markers down the center of the road bounce your high-beams back at you.

Highway retroreflectors in action. Image credit: Wikimedia Commons/Public Domain

We’ve seen some pretty nifty image comparisons demonstrating the Seeliger effect on Saturn, but as of yet, we haven’t seen an animation of the same. Certainly, such a feat is well within the capacities of amateur astronomers out there… hey, we’re just throwing that possibility out into the universe.

Through a small telescope, the moons of Saturn become readily apparent. The brightest of them all is Titan at magnitude +9, orbiting Saturn once every 16 days. Discovered by Dutch astronomer Christiaan Huygens on March 25, 1655 using a 63 millimeter refractor with an amazing 337 centimeter focal length, Titan would easily be a planet in its own right were it directly orbiting the Sun. Titan also marks the most distant landing of a spacecraft ever carried out by our species, with the descent of the European Space Agency’s Huygens lander on January 14, 2005. Huygens hitched a ride to Saturn aboard NASA’s Cassini spacecraft, which is slated to end its mission with a destructive reentry over the skies of Saturn in 2017. Saturn has 62 known moons in all, and Enceladus, Mimas, Tethys, Dione, Rhea and two-faced Iapetus are all visible from a backyard telescope.

You can check out the current position of Saturn’s major moons (excluding Iapetus) here.

And speaking of Iapetus, the outer moon would make a fine Saturn-viewing vantage point, as it is the only major moon with an inclined orbit out of the ring plane of Saturn:

Expect our Saturn observing resort to open there one day soon.

Up for a challenge? Standard features to watch for include: the shadow of the rings on the planet, and the shadow of the planet across the rings, as well as the Cassini division between the A and B ring… but can you see the disk of the planet through the gap? High magnification and steady seeing are your friends in this feat of visual athletics… catching sight of it definitely adds a three dimensional quality to the overall view.

Let ‘the season of Saturn 2015’ begin!

May 10, 2015December 23, 2015 by Bob King

Head Held High, Comet Lovejoy Does the Polar Plunge

Comet C/2014 Q2 Lovejoy on May 7 with its emerald coma and faint gas tail. Lovejoy is currently around magnitude +7.5 and slowly fading. Credit: Rolando Ligustri

Lots of towns hold a polar plunge fundraising event in the winter. Duluth, Minnesota’s version, where participants jump in Lake Superior every February, might just be the coldest. Comet Lovejoy’s a season behind, but sure enough, it’s following suit, diving deep into the dark waters of the north celestial pole this month.

I dropped in on our old friend last night, when it glowed only 8° from the North Star. In 8×40 binoculars, the comet was faintly visible as a hazy blob of light with a brighter center. Not a sight to knock you over, but the fact that this comet is still visible in binoculars after so many months makes it worthwhile to seek out. Moonless skies for the next 10-11 nights means lots of opportunities.

Just face the North Star (Polaris) to begin tracking Comet Lovejoy. Stars are shown to magnitude +8. Click for a larger version. Created with Stellarium — Just face the North Star (Polaris) to begin tracking Comet Lovejoy. The map shows the sky facing north around 10:30 p.m. local time in mid-May. Stars are plotted to magnitude +8. Click for a larger version. Source: Chris Marriott’s SkyMap

Unless a new comet is discovered, Lovejoy will continue to remain the only “bright” comet visible from mid-northern latitudes for some time. There’s a tiny chance Comet C/2014 Q1 PanSTARRS will wax bright enough to see in twilight in early July, but it will be very low in the northwestern sky at dusk and visible for a few nights at most. Only C/2013 US10 Catalina offers the chance for a naked eye / binocular appearance, when it re-emerges from the solar glare in the latter half of November in the morning sky.

Southern hemisphere observers have more to smile about with Comet C/2015 G2 MASTER currently flaunting its fluff at magnitude +6.6 or just under the naked eye limit. They’ll also get a far better view of C/2014 Q1 PanSTARRS come this July and August.

Wide view of the sky facing north in mid-May around 10:30 p.m. local time. Use the Pointer stars in the Big Dipper to point you to Polaris and from there to the comet. Source: Chris Marriott's SkyMap — Wide view of the sky facing north in mid-May around 10:30 p.m. local time. Use the Pointer stars in the Big Dipper to point you to Polaris and from there to the comet. Source: Chris Marriott’s SkyMap

Through a telescope, Lovejoy still shows off a round, 6 arc minute diameter coma (one-fifth as wide as a full moon) and a denser, brighter core highlighted by a starlike false nucleus. We call it false because the true comet nucleus, probably no more than a few kilometers across, hides within a dusty cocoon of its own making. Only spacecraft have been able to get close enough for a clear view of comet nuclei. Each shows a unique and usually non-spherical shape because comets aren’t massive enough for their own self-gravity to crush them into spheres the way larger moons and planets do. If you’re a single object and big, being spherical comes naturally.

Comet Lovejoy will be closest to the imaginary point in the sky called the north celestial pole on May 29. Polaris lies 0.75° from the pole and describes a small circle 1.5° in diameter around it each day. Source: Stellarium

In my 15-inch (37-cm) telescope a faint wisp of a tail poked from the coma to the north. Looking at the map, you can see the comet’s headed due north through Cepheus toward Polaris, the North Star. Each passing night, it draws closer to the sky’s celestial pivot point, missing it by just 1° on the evenings of May 27 and 28. Closest approach to the north celestial pole, which marks the spot in the sky toward which Earth’s north polar axis currently points, occurs on May 29 with a separation of 54 arc minutes or just under a degree.

Finding Polaris is easy. Just draw a line through the two stars at the end of of the Big Dipper’s Bowl toward the horizon. The first similarly bright star you run into is the North Star. Using the map, you can navigate from Polaris to the fuzzy comet with either binoculars or telescope.

May 7, 2015December 23, 2015 by David Dickinson

Tales (Tails?) of Two Comets: Prospects for Q1 PanSTARRS & G2 MASTER

Comet G2 MASTER passes near the Helix Nebula in Aquarius on the night of April 21st.

Did you catch the performance of Comet C/2014 Q2 Lovejoy earlier this year? Every year provides a few sure bets and surprises when it comes to binocular comets, and while we may still be long overdue for the next truly ‘Great Comet,’ 2015 has been no exception.

This week, we’d like to turn your attention to two icy visitors to the inner solar system which may present the best bets comet-wise over the next few weeks: Comets C/2014 Q1 PanSTARRS and C/2015 G2 MASTER.

First up is Comet C/2014 Q1 PanSTARRS. Discovered on August 16, 2014 by the Panoramic Survey Telescope & Rapid Response System (PanSTARRS) based atop Mount Haleakala in Hawaii, we’ve known of the potential for Q1 PanSTARRS to put on a decent show this summer for a while. In fact, it made our roundup of comets to watch for in our 101 Astronomical Events for 2015. Q1 PanSTARRS currently sits at +11^th magnitude as a morning sky object in the constellation Pisces. On a 39,000 year long parabolic orbit inclined 45 degrees relative to the Earth’s orbit, Q1 PanSTARRS will leap up across the ecliptic on May 17^th and perhaps reach +3^rd magnitude as it nears perihelion in early July and transitions to the evening sky.

An image of Comet C/2014 Q1 PanSTARRS shortly after discovery. Credit and copyright: Efrain Morales Rivera.

Though it may put on its best show in July and August, a few caveats are in order. First, we’ll be looking at Q1 PanSTARRS beyond the summer Sun, and like C/2011 L4 PanSTARRS a few years back, it’ll never leave the dusk twilight, and will always appear against a low contrast backdrop.

May June (AM) Starry Night Education software. — The May-June path of Comet Q1 PanSTARRS through the dawn sky as seen from latitude 30 degrees north. Credit: Starry Night Education software.

Here are some notable upcoming events for Comet C/2014 Q1 PanSTARRS:

(Unless otherwise noted, a ‘close pass’ is here considered to be less than one degree of arc, about twice the diameter of a Full Moon.)

May 16: Passes into the constellation Aries.

May 16: The waning crescent Moon passes 2 degrees distant.

May 17: Crosses northward through the ecliptic.

May 20: May break +10^th magnitude.

June 11: Passes in to the constellation Taurus.

June 12: Passes 2 degrees from M45 (The Pleiades).

June 15: May break 6^th magnitude.

June 20: Passes into Perseus.

June 21: Passes into Auriga.

June 23: Passes +2.7 magnitude star Hassaleh (Iota Aurigae).

June 25: Passes the +7.5 magnitude open cluster IC 410.

June 26: Passes +6 magnitude Pinwheel Open Cluster (M36).

Evening path. Starry Night Education software. — The July-August evening path of Q1 PanSTARRS as seen from latitude 30 degrees north. Credit: Starry Night Education software.

July 2: Crosses into Gemini.

July 3: Passes the +3.6 magnitude star Theta Geminorum.

July 5: Passes 10 degrees north of the Sun and into the evening sky.

July 6: Passes midway between Castor and Pollux.

July 6: Reaches perihelion at 0.315 astronomical units (AU) from the Sun.

July 7: May top out at +3^rd magnitude.

July 8: Crosses into Cancer.

July 12: Photo Op: passes M44, the Beehive Cluster.

July 13: Sits 30 degrees from Comet C/2015 G2 MASTER (see below).

July 15: May drop below +6^th magnitude.

July 15: Crosses the ecliptic southward.

July 17: The waxing crescent Moon passes 1.5 degrees south.

July 19: Crosses into Leo.

July 20: Closest to Earth, at 1.18 AU distant.

July 21: Less than 10 degrees from Jupiter and Venus.

July 22: Crosses into Sextans.

July 26: Crosses the celestial equator southward.

August 4: Crosses into Hydra.

August 5: Crosses into Crater.

August 18: Crosses back into Hydra.

August 30: Crosses into Centaurus.

September 1: Drops below +10^th magnitude.

Light curve. — The projected light curve of Q1 PanSTARRS over time. The black dots represent observations. Credit: *Weekly Information about Bright Comets*.

The next comet on deck is the recently discovered C/2015 G2 MASTER. If you live in the southern hemisphere, G2 MASTER is the comet that perhaps you haven’t heard of, but should be watching in the dawn sky. Discovered last month on April 7 as by MASTER-SAAO (The Russian built Mobile Astronomical System of Telescope-Robots at the South African Astronomical Observatory), this is not only the first comet bagged by MASTER, but the first comet discovery from South Africa since 1978. G2 MASTER has already reached magnitude +7 and is currently crossing the constellation Sculptor. It is also currently only visible in the dawn sky south of 15 degrees north latitude, but images already show a short spiky tail jutting out from G2 MASTER, and the comet may rival Q2 Lovejoy’s performance from earlier this year. Expect G2 MASTER to top out at magnitude +6 as it nears perihelion in mid-May. Observers around 30 degrees north latitude in the southern U.S. should get their first good looks at G2 MASTER in late May, as it vaults up past Sirius and breaks 10 degrees elevation in the evening sky after sunset. Again, as with Q1 PanSTARRS, cometary performance versus twilight will be key!

An April 10th image of Comet C/2015 G2 MASTER, plus an initial projected light curve versus solar elongation over time. Credit: Ernesto Guido & Nick Howes/Remanzacco Observatory

Here are some key dates with astronomical destiny for Comet G2 MASTER over the coming weeks:

May 9: Crosses into Fornax.

May 15: May top out at +6^th magnitude.

May 13: Closest to Earth at 0.47 AU.

May 14: Crosses into Eridanus.

May 16: Crosses into Caelum.

May 17: Crosses into Lepus.

May 20: Passes the +3.8 magnitude star Delta Leporis.

May 23: Crosses into Canis Major.

May 23: Reaches perihelion at 0.8 AU from the Sun.

May 27: Crosses into Monoceros.

May 28: Passes the +5.9 magnitude Open Cluster M50.

Comet G2 MASTER imaged on May 7th. Credit and copyright: Adriano Valvasori

June 8: Crosses northward over the celestial equator and into the constellation Canis Minor.

July 1: May drop below 10^th magnitude.

G2 MASTER also crosses SOHO’s field of view on July 24^th through August 4^th, though it may be too faint to see at this point.

Here are the Moon phases for the coming weeks to aid you in your comet quest:

Full Moons: June 2^nd, July 2^nd, July 31^st, August 29^th.

New Moons: May 18^th, June 16^th, July 16^th, August 14^th.

Binoculars are our favorite ‘weapon of choice’ for comet hunting. Online, Heavens-Above is a great resource for quickly and simply generating a given comet’s sky position in right ascension and declination; we always check out the Comet Observers Database and Seiichi Yoshida’s Weekly Information about Bright Comets to see what these denizens of the outer solar system are currently up to.

Good luck, and be sure to regale us with your comet-hunting tales of tragedy and triumph!

April 30, 2015December 23, 2015 by Bob King

Mercury MESSENGER Mission Concludes with a Smashing Finale!

The image shown here is the last one acquired and transmitted back to Earth by the mission. The image is located within the floor of the 93-kilometer-diameter crater Jokai. The spacecraft struck the planet just north of Shakespeare basin. The image measures 0.6 miles (1 km) across. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

The planet Mercury has a brand new 52-foot-wide crater. At 3:26 p.m. EDT this afternoon, NASA’s MESSENGER spacecraft bit the Mercurial dust, crashing into the planet’s surface at over 8,700 mph just north of the Shakespeare Basin. Because the impact happened out of sight and communication with the Earth, the MESSENGER team had to wait about 30 minutes after the predicted impact to announce the mission’s end.

NASA estimates that the MESSENGER spacecraft would crash into Mercury this afternoon at 3:26 p.m. EDT near the 30-mile-wide crater Janacek on the opposite side of the planet from Earth. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington — NASA predicted that the MESSENGER spacecraft would crash into Mercury this afternoon at 3:26 p.m. EDT near the 30-mile-wide crater Janacek and the large Shakespeare Basin on the opposite side of the planet from Earth. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Even as MESSENGER faced its demise, it continued to take pictures and gather data right up until impact. The first-ever space probe to orbit the Solar System’s innermost planet, MESSENGER has completed 4,103 orbits as of this morning. Not only has it imaged the planet in great detail, but using it seven science instruments, scientists have gathered data on the composition and structure of Mercury’s crust, its geologic history, the nature of its magnetic field and rarefied sodium-calcium atmosphere, and the makeup of its iron core and icy materials near its poles.

Color-coded view of Carnegie Rupes (ridge) with low elevations in blue and high in red. The ridge formed as the Mercury's interior cooled, resulting in the overall shrinking of the planet. Parts of the landscape lapped over other parts as the planet shrunk. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington — Color-coded view of Carnegie Rupes at left with low elevations in blue and high in red. The ridge formed as Mercury’s interior cooled, resulting in the overall shrinking of the planet. Parts of the landscape lapped over other parts as the planet shrunk. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Images show those ubiquitous craters but also features that set its moonlike landscape apart from the Moon including volcanic plains, tectonic landforms that indicate the planet shrank as its interior cooled and mysterious mouse-like nibbles called “hollows”, where surface material may be vaporizing in sunlight leaving behind a network of holes. To learn more about the mission’s “greatest hits”, check out its Top Ten discoveries or pay a visit to the Gallery.

The rounded, depressions, called "hollows", are a fascinating discovery of MESSENGER's orbital mission and may have been formed by vaporization of something in the material when exposed by the Raditladi impact. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington — The rounded depressions, called “hollows”, are a fascinating discovery of MESSENGER’s orbital mission and may have been formed by vaporization of materials in the surface when exposed by the Raditladi impact. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

MESSENGER mission controllers conducted the last of six planned maneuvers on April 24 to raise the spacecraft’s minimum altitude sufficiently to extend orbital operations and further delay the probe’s inevitable impact onto Mercury’s surface, but it’s now out of propellant. Without the ability to counteract the Sun’s gravity, which is slowly pulling the craft closer to Mercury’s surface, the team prepared for the inevitable.

False color images of Mercury taken with MESSENGER's Mercury Atmosphere and Surface Composition Spectrometer (MASCS) in everything from infrared to ultraviolet light reveal colorful differences in terrain and surface mineralogy. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington — False color images of Mercury taken with MESSENGER’s Mercury Atmosphere and Surface Composition Spectrometer (MASCS) in everything from infrared to ultraviolet light reveal colorful differences in terrain and surface mineralogy. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

The spacecraft actually ran out of propellant a while back, but controllers realized they could re-purpose a stock of helium, originally carried to pressurize the fuel, for a few final blasts to keep it alive and doing science right up to the last minute. During its final hours today, MESSENGER will be shooting and sending back as many new pictures as possible the same way you’d squeeze in one last shot of the Grand Canyon before departing for home. It’s also holding hundreds of older photos in its memory chip and will send as many of those as it can before the final deadline.

Farewell MESSENGER! Artist view of the spacecraft orbiting the innermost planet Mercury. Credit: NASA — Farewell MESSENGER! Artist view of the spacecraft in orbit about Mercury. Credit: NASA

“Operating a spacecraft in orbit about Mercury, where the probe is exposed to punishing heat from the Sun and the planet’s dayside surface as well as the harsh radiation environment of the inner heliosphere (Sun’s sphere of influence), would be challenge enough,” said Principal Investigator Sean Solomon, MESSENGER principal investigator. “But MESSENGER’s mission design, navigation, engineering, and spacecraft operations teams have fought off the relentless action of solar gravity, made the most of every usable gram of propellant, and devised novel ways to modify the spacecraft trajectory never before accomplished in deep space.”

Face northwest starting about 45 minutes after sunset to look for Mercury tonight. It will lie about two fists below Venus and only 1.5 from the Pleiades star cluster. Source: Stellarium — Face northwest starting about 45 minutes after sunset to find Mercury tonight. It’s located about two fists to the lower right of Venus and just 1.5° below the Pleiades star cluster. Use binoculars to see the star cluster more easily. Source: Stellarium

Ground-based telescopes won’t be able to spy MESSENGER’s impact crater because of its small size, but the BepiColombo Mercury probe, due to launch in 2017 and arrive in orbit at Mercury in 2024, should be able to get a glimpse. Speaking of spying, you can see the planet Mercury tonight (and for the next week or two), when it will be easily visible low in the northwestern sky starting about 45 minutes after sundown. The planet coincidentally makes its closest approach to the Pleiades star cluster tonight and tomorrow.

Use the occasion to wish MESSENGER a fond farewell.

April 30, 2015December 23, 2015 by David Dickinson

Crossing Quarters: Would the Real Astronomical Midway Point Please Stand Up?

Happy May Day Eve!

Maybe May 1^st is a major holiday in your world scheme, or perhaps you see it as the release date of Avengers: Age of Ultron.

We’re approximately mid-way between the March equinox and the June solstice this week, as followers of the Gregorian calendar flip the page tomorrow from April to May. Though astronomical spring began back on March 20^th for the northern hemisphere, May 1^st is right around the time it starts to feel like spring weather for most of the residents of mid- northern latitudes.

Blame solar insolation, as the Sun transits ever higher in its daily trek towards the June solstice. Sure, the 23 degree 26’ 21” axial tilt of our fair planet is the reason for the season, and the pair of equinoxes and solstices are easily marked… but did you know that there are four other astronomical waypoints along the ecliptic that aren’t so readily defined?

A ‘sidewalk sundial’ in front of the Flandrau observatory in Tucson, Arizona. Credit and copyright: Dave Dickinson

Welcome to the curious world of cross-quarter days. Tomorrow, May 1^st is also known as May Day, which is one such holiday. Perhaps, if you’re reading this in the remaining socialist states of China, Cuba or North Korea, you observe May Day as a major communist holiday. True story: back in our Cold Warrior days, May Day usually meant deployment to a forward location to chase Soviet Bear bombers out of friendly air space.

The cycle of four cross quarter days and four quarter (two solstices and two equinoxes) comprise the modern ‘Wheel of the Year’ on the Pagan calendar. The Christian holidays of Easter and Christmas also have their equinoctial and solstice roots.

The other three cross quarter holidays on our modern calendar are: Groundhog Day (February 2nd), Lammas Day (August 1st) and Halloween on October 31^st. It’s great to see suburbanites don garb and request treats in a yearly re-enactment of ancient ritual.

But the solstice and equinoctial points aren’t fixed on the Gregorian calendar, but instead drift as we attempt to keep measured time in sync with astronomical time. These midway dates should actually be referred to as ‘cross-quarter tie-in holidays,’ as the actual midpoint between solstice and equinox can be determined in several different ways.

Here are the technical mid-points for 2015:

*Note that Easter in the Catholic Church is defined by the First Council of Nicaea in 325 A.D. as the first Sunday after the First Full Moon after March 21^st. It can, therefore, fall anywhere from March 22nd to April 25th. The Eastern Orthodox Church uses the older Julian calendar, meaning the dates of Easter for the two sects of Christianity do not always coincide. Keep in mind, however, that March 21^st is only an approximation for the northward equinox, which, in the 20^th through 21^st century, can fall anywhere from March 19^th to March 21st.

Marking the technical midway point in declination simply means noting when the Sun crosses 11 degrees 43’ 10” north or south. Note that these always cluster with a bias towards the equinoxes, as the apparent motion of the Sun is faster in declination as it moves at a steeper angle around these dates. Sol’s motion in declination is shallowest near the solstices, which is why the gain and loss of daylight is least noticeable around these dates.

The true position of the Sun on May 1st. Credit: Stellarium

And the second way we can mark the technical midpoints is strictly in time… but keep in mind, the seasons are not precisely equal in length due to the elliptical orbit of the Earth. Though it may not seem like it, Earth actually reaches perihelion and moves slightly faster around the Sun in early January during the depths of northern hemisphere winter!

And our friend the precession of the equinoxes plays a role as well, moving the two equinoctial points where the ecliptic and the celestial equator intersect once all the way around the sky as the Earth completes one ‘wobble’ every 26,000 years… live out a typical 72 year life span, and the equinoctial points will have moved about one degree, or twice the diameter of a Full Moon.

An Earthbound analemma simulation. Credit: Starry Night Education Software

And you can ‘observe’ the motion of the Sun and trace out the figure 8 shape of the analemma noting the quarter and cross-quarter points by imaging the Sun at the same time of the day once every week or so for a year:

Note: make sure you stay on local solar time in your yearlong analemma quest… don’t let the archaic vagaries of Daylight Saving Time throw you off by an hour!

Mars analemma. Credit: — A Mars analemma as seen from Opportunity. Credit: NASA/JPL/Cornell/ASU/TAMU

And other planets have extraterrestrial analemmas as well. In the case of Mars, the path of the Sun over the Martian year is actually teardrop-shaped:

However you reckon the springtime mid-point, don’t miss any local ‘May Day-henge’ alignments coming to a horizon near you.