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Late June offers a grab bag of clusters and nebulae "lined up" at the midnight hour. Time your southern deep-sky viewing with meridian passage and you'll be a happy camper.
The meridian's the place to be. No doubt about it. Stars and the deep-sky quarry we all love to explore begin their nightly arc in the east, reach their greatest height above the horizon when crossing the meridian, and then descend into the west.
The meridian begins at the due south point on the horizon, climbs to the zenith, then drops to the due north point on the northern horizon. A celestial object in the southern sky will be at its greatest altitude and seen most clearly through the least amount of atmosphere when crossing the southern meridian. Objects in the northern sky will be highest when they cross the meridian above the polestar and lowest (at nadir) when they cross it below the pole.
I'd be willing to bet most amateurs observe more objects on their way up rather than on their way down. There's a freshness to deep-sky objects when they first appear in the east and the pleasure of knowing that with every passing minute, Earth's rotation carries it higher and higher toward the meridian.
Summertime brings great riches in the eastern sky for skywatchers. One of the richest parts of the Milky Way courses through Scorpius, Ophiuchus, and Sagittarius, filling each of these constellations with visual and photographic treasures: dozens of globulars and planetary nebulae, scores of open clusters and bright nebulae, and too many dark nebulae to count!
How to make sense of it all? There are many ways to break down this bounty into manageable groups. For instance, you can select a bright star and star-hop your way from one deep-sky object to the next, the way you'd jump from rock to rock to ford a creek. Or you could choose to visit all of summer's globular clusters over the course of several nights.
Allow me to offer a slight variation — the "meridian package." Dobsonian owners will find this one of the easier ways to scoop up summer's southern clusters and nebulae. Point your Dob due south, and finding objects will involve a simple up or down push with a nudge east or west.
Of course, timing is everything. That's why I selected midnight local daylight time on July 1st. A ride along the midnight meridian on that date offers an incredible diversity of deep-sky objects within 1°–2° of vertical.
I can offer one for-sure guarantee — the objects, which inhabit the low southern sky, will be seen to their best advantage. So let's get started. The map above shows a strip of sky centered on the meridian with stars to magnitude +9.5 and a selection of deep-sky objects from about 10th magnitude and up. Since the rotating Earth makes everything in the sky a moving target, you might consider beginning a half-hour before midnight to take better advantage seeing them all at maximum altitude.
Midnight may seem late but with twilight not over till after 10:30 p.m. from many locations, the hour arrives sooner than you'd think. Plus you have another option. Thanks to Earth's revolution around the Sun which causes the constellations to drift westward with the seasons, they'll be lined up north-south around 11:30 p.m. on July 8th, 11 p.m. on July 15th, and 10:30 p.m. on July 22nd.
All the objects lie near the Stinger Stars, Shaula and Lesath, in the tail of Scorpius, and concentrate around two bright, naked-eye star clusters, M6, a.k.a. the Butterfly Cluster, and M7, Ptolemy's Cluster. Most are open clusters, but two globulars, several oxymoronic faint, "bright" nebulae from the Sharpless H II list, and a healthy selection of dark nebulae from E. E. Barnard's famous catalog, spice things up.
The table below includes details and brief descriptions for 32 objects. I observed with a 10-inch f/4.5 Dob from northern Minnesota, where few climb higher than 10° during meridian passage. A few eluded my sight, but you may have better luck particularly if you live further south. I started at the Stingers and worked my way northward using the map to star-and-deep-sky-object-hop from one to the next, using magnifications of 57× and 115×.
Here are additional details on a few of my favorites:
* M6 and M7. For sheer brilliance and sparkle, these are incredible in both binoculars and small-sized telescopes. M6 looks like a plump moth, while M7 always reminds me of a sideways letter "K." The misty faint globular NGC 6453 makes for a nice challenge along its western border and an excellent comet imposter!
* What is it about Trumpler open clusters? Nearly every one I've seen has so much character and typically contains a nice mix of brighter stars that overlie a rich, misty backdrop of fainter members. The three on this list are no exception.
* Many Barnard dark nebulae can be low-contrast, difficult objects, but the two flanking M6 (its "ears") and Barnard 286, centered on a single bright star south of M7, stood out well enough at 57× even at their low altitudes.
* NGC 6383 looks like a bright star at first blush, but increase the magnification to around 100× and you'll uncover a dozen faint stars almost hidden in its glare. The stellar clutches of NGC 6451 and NGC 6400 were two more of my favorites. They're both small and lack the glamor of the big clusters, but they compensate with sugar-grain starriness.
Happy summer nights! May you so lose yourself in the spiral arms of the Milky Way that you completely forget the time.Name Mag. SIZE R. A. DEC. Comments Collinder 332 8.9 2′ 17h 31m –37º 04′ Small, faint, nebulous in Lesath's glow Ha 16 ~8 ~15′ 17h 31m –36º 50′ Moderately rich cluster, E-W elongated Collinder 333 9.8 8′ 17h 31m –34º 00′ ~10 stars, loose, not concentrated Barnard 271 ---- 120′ ×
10-15′ 17h 34m –34º 15′ Vague, low contrast dark nebula NGC 6383 5.5 20′ 17h 34m –32º 35′ Nice! 6 mag. star anchors a faint dozen Trumpler 27 6.7 7′ 17h 36m –33º 29′ Tiny bright stellar triangle on w. side. Trumpler 28 7.7 6′ 17h 37m –32º 28′ Very nice! Misty with faint stars. Rich. NGC 6396 8.5 3′ 17h 37m –35º 02′ ~10 stars with two close doubles Collinder 338 8.0 20′ 17h 38m –37º 33′ Couldn't confirm sighting Barnard 273 ---- 15′ 17h 38m –33º 20′ Another vague, low contrast nebula Barnard 275 ---- 13′ × 4′ 17h 38m –32º 19′ One of two dark "ears" either side M6 NGC 6404 10.6 6′ 17h 40m –33º 14′ Bright but sparse NGC 6400 8.8 12′ 17h 40m –36º 57′ Rich with faint stars, very pretty! M6 4.2 33′ 17h 40m –32º 13′ Spectacular! Butterfly cluster. Barnard 278 ---- 15′ × 4′ 17h 42m –32º 18′ Dark "ear" on east side of M6. NGC 6416 5.7 15′ 17h 44m –32º 21′ Cool anchor shape. Moderately rich. Collinder 345 10.9 4.8′ 17h 44m –33º 52′ Loose group of 15-20 stars NGC 6421 star cloud ---- 45′ 17h 35m –33º 41′ Nebulous appearance with faint stars Collinder 347 8.8 10′ 17h 46m –29º 20′ Small, loose cluster, arc-shaped Sharpless 2-16 ---- 20′ 17h 46m –29º 23′ Suspected "haze" with UHC filter. NGC 6425 7.2 10′ 17h 47m –31º 32′ Nice ~25-star brightish group. Sharpless 2-19 ---- 12′ 17h 49m –29º 07′ Not seen with or w/o UHC filter Collinder 351 9.3 8′ 17h 50m –28º 46′ Moderately rich, loose, not a standout Sharpless 2-15 ---- 30′ 17h 50m –31º 16′ Faint misty presence with UHC filter NGC 6441 globular 7.2 9.6′ 17h 50m –37º 03′ Small, bright w/bright core. Granulated. NGC 6451 8.2 8.0′ 17h 50.5m –30º 13′ Lovely stellar thicket of ~50 stars Barnard 283 ---- 75′ × 5′ 17h 51m –33º 52′ Vague except for the darker w. half NGC 6453 globular 10.2 7.6′ 17h 51m –34º 36′ Along w. edge of M7. Faint, comet-like Barnard 286 ---- 15′ × ? 17h 53m –35º 37′ Easy dark spot centered on bright star M7 3.3 75′ 17h 54m –34º 47′ Spectacular! Easy with naked eye. Barnard 287 ---- 30′ × 5′ 17h 54m –35º 11′ Small, dark "spot" with stars at core Trumpler 30 8.8 20′ 17h 56m –35º 19′ Beauty! ~20 stars in a stellar haze
Sources for more information:
The discovery of a chiral molecule in space has the potential to sort out one of the biggest mysteries in the chemistry of life.
Despite college chemistry I never understood chirality’s relevance to life until (of all things) I was diagnosed with asthma. I received a prescription for albuterol, but it made me feel shaky and out of sorts. Turns out that albuterol is actually a mix of two “handed”, or chiral molecules, identical in chemical formula but very different in how they act on the body.
Like hands, the two versions of albuterol are mirror images of each other, with a hydrogen atom that sticks out like a sore thumb. “Right-handed” albuterol binds to receptors and dilates airways during an asthma attack. The left-handed version doesn’t. Its mirror-image shape keeps it from interacting with airway receptors, so it wanders around the body causing unintended side effects instead.
In fact, all of life’s chemistry seems to be based on chiral molecules of a certain handedness, a concept known as homochirality. All the amino acids that make up life’s proteins are left-handed, the sugars that form the helical backbone of DNA are all right-handed, and so on.
But why has life tied itself to right-handed sugars or left-handed proteins — why not the other way around? The answer, it turns out, might lie in the stars.Why is Life Left- (and Right-) Handed?
Scientists have come up with a number of ideas to explain homochirality. To name a few: maybe it arose by chance — the chemistry for life just started one way and kept on going. Or maybe life arose using multiple chemistries but molecules of one handedness provided some evolutionary advantage.
Or, and here’s where it gets astronomically interesting, maybe the molecules on Earth started out with a preference for one hand over another. As chemist Francis Japp said in 1894: “Only asymmetry can beget asymmetry.” The imbalance we see now could have been forged during the formation of the solar system. Indeed, meteorite studies confirm the imbalance was already present early on.
Here’s how it might have worked. The harsh radiation of stellar nurseries destroys fragile prebiotic molecules that form in interstellar space. But amidst the dust of star formation, that radiation can become polarized — that is, forced to undulate along a certain direction. Polarized radiation could destroy slightly more molecules of one hand than the other, creating an initial asymmetry.First Chiral Molecule in Space
Brett McGuire (National Radio Astronomy Observatory) and colleagues are seeking to test the origin of one-handed life as part of their Prebiotic Interstellar Molecular Survey (PRIMOS), conducted with the Green Bank Telescope.
To find the chemical fingerprint of various molecules around stars-to-be, the PRIMOS project examined a giant cloud of dust and gas near our galaxy’s center dubbed Sgr B2(N) between frequencies of 1 and 50 GHz. Spanning 150 light-years, Sgr B2(N) is one of the largest giant molecular clouds in the galaxy. Though much of its 3 million solar masses’ worth of dust and gas is hydrogen, it’s already the famous home to vast quantities of complex organic molecules such as ethanol, and even a simple sugar known as glycolaldehyde.
Now it’s home to one more intriguing molecule. In the June 17th Science (full text here), McGuire’s team reported the first discovery of a chiral molecule in space. Using GBT, as well as the Parkes Radio Telescope in Australia, the team measured the spectra of the glowing cores that will one day be full-fledged stars. A chiral molecule, propylene oxide, left its chemical fingerprint in this spectrum, absorbing three narrow bands of radio waves.
The team’s current data can’t distinguish between right-handed and left-handed propylene oxide — they’ve just shown that the molecule’s there. But it can be done. The authors were studying radio waves of all types, but if astronomers home in on polarized radio waves, they should be able to separate out the left-handed molecules from the right-handed ones. If asymmetry is already there, we’ll see it.Bringing Prebiotic Molecules Home
It’s worth noting that propylene oxide isn’t found directly among the hot protostars of Sgr B2(N) — it lies in a surrounding shell of cold gas at just a few degrees above absolute zero. The molecules are probably coming together on icy dust grains far from the heat of star formation. But if they’re going to be used for life, such molecules eventually have to fall into star- and planet-forming regions.
Direct evidence of this process comes from a recent study using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. Yoko Oya (The University of Tokyo) and colleagues found a ring of organic molecules (methyl formate and carbonyl sulfide) rotating around a Sun-like protostar at 50 times the Earth-Sun distance. The ring marks the outer boundary of the disk of dust and gas that spins around the still-forming star.
Read more on Oya’s results in ALMA’s press release.
Amateur astronomy has lost a dedicated observer and successful visual comet hunter.
Rolf Meier was born in Ottawa in 1953. As a teenager, he read about the great effort that the American astronomer Clyde Tombaugh went through to discover Pluto. Hooked on the night sky, Rolf joined the Royal Astronomical Society of Canada's Ottawa Centre, one of Canada's most active and noted astronomy clubs, and he became an frequent observer.
In 1975, Kathy Hall, another active member there, suggested that some enthusiasts who enjoy spending long hours looking at the sky might enjoy searching for comets. The idea certainly caught Rolf's attention. Although he'd begun a casual search of the evening sky, in those early years his professional interest revolved around engineering. He went to Carleton University, from which he earned a degree in electronics two years later in 1977.
By then Rolf's interest in astronomy had become even more serious. Using the large 16-inch reflector at the Ottawa Centre's Indian River Observatory, he prided himself on using a telescope several times larger than what most other searchers use. "I never wanted to push myself," he said. "I'd just look when it was convenient. I'm not in it for the discomfort," he added with his famous dry wit.
On the evening of April 26, 1978, after searching for only 50 hours, he discovered his first comet — and the first one ever found from Canada. Comet Meier, initially designated 1978f and later C/1978 H1, is one of the largest comets ever found by anyone. Despite a perihelion distance of just 1.14 astronomical units, it never got bright enough to be viewed without a telescope. Still, it hung about for more than a year at the edge of visibility.
Most comets are relatively small balls of icy mud, traveling around the Sun in long, looping paths that often pass through the inner solar system only once. When a comet nears the Sun, however, its ices sublimate, turning to ionized gas, and then the comet gets bright enough to be followed. To see a comet is rare, to find one rarer still. And to catch one from the frequently cloudy sky over Canada, after only 50 hours of looking, is unheard of — and that is what Rolf did.
One comet find, people say, is an accident. Rolf knew this, and so he quickly resumed his search. Only 18 months later, after only 29 more hours of searching, he found his second comet — and then a third one less than a year after that.
Meanwhile, he'd found a partner in Linda McCrae, another active amateur in the Ottawa club. Before their wedding in 1984, Linda gave Rolf an oil painting. But in return she asked him to give her another new comet. Two months after tying the knot, Rolf obliged. They were observing together with friends. "My Linda!" Rolf would call loudly across the observing field. "My Rolfi!" Linda would respond. But then, urgently, came a second call: "Linda! I think I've got one." By the time their son Matthew was born the next year, Rolf had four comets to his credit, and has been one of Canada's most highly respected citizens ever since.
Rolf continued his journey in astronomy by night and kept working as an engineer by day. As Ottawa Centre past president Gary Boyle recalls, Rolf would often share his planetary photography (another passion) at the club's monthly meetings, and the Meiers would host an annual cookout and occasional meteor watches at their home.
One day this past spring, he went to work as usual. But a few hours later he telephoned Linda with a terrible headache; he could hardly move. She drove him to a hospital, where he was diagnosed with a stage IV brain tumor. He died peacefully on June 26th at age 63.
The October 2016 issue of Sky & Telescope features our latest understanding of Eta Carinae's Great Eruption, the massive blast that turned a nondescript (binary) star into the second-brightest in the sky. Thomas Madura, Steffen Wolfgang, and colleagues combined observations of gas motions in the Homunculus Nebula with 3D-rendering software called Shape to generate a model that you can rotate on your screen or even, if you have a 3D printer, touch with your hands.Observing Eta Carinae in 3D
This animation sequence zooms into a Hubble image of the Homunculus Nebula, then dissolves to the 3D-rendered model, which rotates to provide views from various angles.
Credit: NASA's Goddard Space Flight Center / CI Lab
Watch the Thomas Madura (then at NASA Goddard) and Ted Gull (NASA Goddard) explain how they and colleagues created the 3D model of the Homunculus:
The same Shape software was later applied to simulations of the stellar winds emanating from the binary star's at the center of the Homunculus.
The authors have also 3D-printed individual frames from this simulation:
A modest proposal: the golden spike that marked the beginning of the Anthropocene was the first lunar landing in Mare Tranquilitatis.
A far-future geologist studying Earth history would observe that our time was one of sudden and unprecedented planetary changes. Could this be a type of transition that other planets also go through, when cognitive systems begin to influence global systems?
I’ve written before about the proposal to formally rename our current geological epoch the Anthropocene (see S&T's April 2013 issue) to acknowledge the fact that humans have become a major force of global modification. Within geological and other academic circles it’s been contentious but fruitful — sparking interesting debates about how we humans should regard, and attempt to guide, our own planet-altering presence.
There’s no consensus over when exactly this humanized age began. Did it arise with the first atomic bomb explosions in the 1940s? If there was ever a time when we started to realize we were all in the same boat, shooting holes in the hull, it was the dawn of the nuclear age. We began to see what we’d become, and it left an indelible isotopic signature. This provides what geologists call a “golden spike,” a unique time stamp associated with an event or transition. Others place the onset of the Anthropocene at the beginning of the Industrial Revolution, or thousands of years earlier when we first undertook large-scale modification of landscapes.
These arguments are most valuable if we read them as a protracted dialogue on how humanity has journeyed from being just another hominid species in East Africa to the global force we are today. I view them as a series of waypoints, each proposed origin marking a different stage in the “hominization” of the planet. Looked at in this way, there is no single, correct moment of genesis.Finding the Golden Spike in the Rock Record
But if geologists are going to formalize the definition, they need to pin it to a specific stage in the rock record. So let me offer my own modest proposal for a “golden spike” to mark the Anthropocene. If we must choose one geological deposit that announces the human presence, I would suggest the area of Mare Tranquillitatis where Apollo astronauts first stepped onto another world, leaving a flag, machines, and footprints.
Those boot marks will fade in a few million years as micrometeorites grind them into the dust, but signs of our presence, including the alien artifacts we left, will be detectable for as long as there is an Earth and a Moon. These lunar landmarks could not have been made by a species without world-changing technology. This altered landscape also captures the moment we first looked back and saw the unity of our home and our common destiny with all life on our planet.
Of course, as an actual proposal for correlating geological events on Earth, a Tranquility Base golden spike is ridiculously impractical. But so what? There is nothing practical about the decision to formalize the Anthropocene Epoch. Any geologists, human or alien, studying our time millions of years from now will not care about our nomenclature. This is all about symbolism and our self-image as we confront the challenges of this new age. So, I know I’ll lose but I vote for Tranquility Base.
Join Sky & Telescope Observing Editor JR Johnson-Roehr in Iceland and see the aurora borealis.
I’ve cleared my calendar for the first week of October. I’ll be in Iceland that week, touring the countryside during the day and chasing the northern lights at night. On October 2nd, I’ll be meeting a group of like-minded individuals in Reykjavík, Iceland’s capital. Together, we’ll watch for auroral outbursts, traveling to dark-sky sites away from the city for the best views. During the day, we’ll explore Iceland’s history, its unique geology and topography, and its best recreational sites.
Spears Travel is wrapping up preparations for the trip, so book now!
Seeing the northern lights is weather dependent, of course, but we’ll have viewing possibilities every night during one of the best parts of the year for aurora activity. The tour takes place in October because more vivid light displays occur in the spring and fall. Plus, we’ll be arriving in Iceland just after new Moon, when the night sky is at its darkest.
I’m looking forward to watching the northern lights with you, and I’m also looking forward to talking to you about auroras and solar science. I’ll be giving two presentations during the week, both focused on the Sun and its effects. I’ll talk about aurora and space weather during my first presentation — what causes the northern lights? — but I’ll also share a bit of the history of solar research: how do we know what we know and when did we learn it? For this, I’ll be drawing on recent work at the Indian Institute of Astrophysics in Bangalore and Kodaikanal Observatory, one of the early stations of solar science.
The Sun also stars in my second presentation, during which I’ll discuss the August 2017 total solar eclipse. For those of us in North America, the eclipse will truly be a once in a lifetime experience, and I want to make sure you know everything you need to know to about this sure-to-be-spectacular event — all questions welcome!
But don’t worry, this week won’t be all about me talking. With our fantastic Icelandic guide, we’ll be touring Reykjavík, the Snæfellsnes Peninsula, and Iceland’s “Golden Circle,” all part of an itinerary featuring waterfalls, geysers, and Viking history. I recently took — and loved — a course on landscapes and Icelandic Sagas, so I’m particularly excited to see the land of the Snæfellsjökull glacier, which features in the Eyrbyggja Saga. You might know Snæfellsjökull as the volcano Jules Verne uses as a starting point in his Journey to the Center of the Earth. Either way — very exciting!
Sound fun? I hope so, and I hope you’ll join me in this adventure!
Why, and how, you should sketch your observations through a telescope.
In the late-1990s, I wrote an essay for a literary journal and cited two quotes: one from an 1851 anonymous French book collector (“Owning a book puts it in your possession, but only reading a book makes it yours”) and the second from renowned literary critic Edmund Wilson (“No two persons read the same book”) Both quotes relate to why I made sketching a regular component of my observing routine.
When you locate and observe a celestial object, it produces a visual experience and another checked box on your “objects seen” list. You move on to the next target, and just as quickly to the one after that. The impression of the object you observed only minutes ago is already dim and quickly being forgotten.
But that’s not the case if you regularly sketch what you observe. You have to slow down and actually study what you see in the field of view. You look at it through various eyepieces, see it in its entirety — close, large, and bold — and as part of a larger celestial context — smaller, and more subdued.
Then you put pencil to paper and sketch it, one star at a time.
Or perhaps you sketch it twice: once at a high magnification to capture all the detail and maximum star count, and a second time to see the object and the surrounding star field, the total celestial tapestry. By the time your sketch is done, you will have spent a half hour, sometimes more, in the company of this single object. Moreover, you will have a permanent and personal hard copy of what you observed. In the spirit of the Frenchman, you will have made the object yours.
And in the spirt of Wilson, no two observers see the same object. If you visit a sketching site, such as Deep Sky Archive or Astronomy Sketch of the Day and look up any object, you will see a dozen sketches, often more, by different observers – and no two look remotely alike. You would think you were looking at sketches of 12 different objects. Over a year ago, S&T Contributing Editor Sue French introduced me to this site and I thought it’d be a great place to reference for my first-time searches. While I found the sketches useful, they were also confusing. Even something as clear and uncomplicated as the Pleiades will have as many variations as there are sketches.
This isn’t a bad thing: it’s one more reason to make every object “yours” by laying out on paper the testimony of your visual senses for each object you observe on that night in those skies with that instrument and those eyepieces.
I’ve been observing for just over three years, but my background is in the humanities. I have zero expertise — or close to zero — in the hard sciences. I am primarily an observer who enjoys taking in the beauty of the nighttime sky. I pay scant attention to technical details and just go hunt down what I want to observe. Once I have found the object in the eyepiece, I leave it there for a while. Sometimes I do a sketch.The Sketching Process
I began to sketch almost as soon as I started observing, but my early sketches would have made third graders laugh at how bad they were. As with most things, my sketches have gotten better the more I practice. My favorite objects are open clusters. I prefer to look at them through one of my refracting telescopes as opposed to my Dobsonian telescopes. With a Celestron 8-to-24-mm zoom eyepiece in place for the first observation, I can change the magnification: up close with the maximum number of stars – or the widest field possible, which puts the object in context to the other stars in the sky. Once I find the ideal magnification, I use one of my fixed focal length eyepieces, often an ES 16 mm or Agena flat-field 19 mm. Then I actually start to sketch the celestial object.
I have a small lined notebook that I use at the telescope to record a very rough first draft. I focus on getting accurate relative positions of the stars, taking care to use different sized dots for individual stars to represent their brightness. I start with the outermost stars in all four directions, just to make sure that I get the entire image I want. Then I sketch the biggest or brightest stars to get the main pattern. Once this is done, I work outward from there, one section at a time.
The next day, I transfer the image onto my artist’s sketchbook, often using a plastic template for the larger stars to ensure I get perfectly round dots. When I have completed the entire sketch, I trace over the larger stars with a darker pencil to distinguish them from the other background stars, and so they look as they do through the eyepiece. In fact, I often take the final draft out one more time and fine tune the sketch based on what I see through the eyepiece.
This is what works for me – and I was thrilled to have one of my renderings appear among so many other fine sketches in June’s Sky & Telescope. What works for you might be completely different. In any case, I’d like to think that this centuries-old technique is seeing a resurgence of interest. With the current fixation on astrophotography, it might be time for a retro focus on the Old School methods.
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A recently discovered minimoon, the asteroid known as 2016 HO3, follows Earth in its orbit around the Sun.
Our fair planet has a tiny companion, a minimoon that shares our annual journey around the Sun in a complex dance.
Astronomers recently announced the discovery of 2016 HO3, an asteroid between 40 and 100 meters in size that behaves as Earth's quasi-satellite. Discovered on April 27, 2016, by the Pan-STARRS 1 survey based on Haleakala, Hawai'i, 2016 HO3 glows dimly at 24th magnitude. 2016 HO3 is in one of the most stable orbits known for a TCOs (Temporarily Captured Object) in orbit around Earth. Calculations suggest that, though it evaded detection until this year, 2016 HO3 has hung out in Earth's vicinity for a century or so, and will remain in a cosmic dance with our world for centuries to come.
“Since 2016 HO3 loops around our planet, but never ventures very far away as we go around the Sun, we refer to it as a quasi-satellite of Earth,” says Paul Chodas (NASA Jet Propulsion Laboratory). “In effect, this small asteroid is caught in a little dance with Earth.”The Weird Orbit of a Minimoon
2016 HO3's orbit takes it alternately sunward and ahead of Earth for six months at a time, before our planet's gravity grabs it and drags it back, forcing it to play catch up. This strange motion is slightly tilted relative to the ecliptic plane, resulting in a corkscrew twist in the orbit over several decades. Too distant to be considered a true second moon, 2016 HO3's journey takes it as close as 38 times the Earth-Moon distance (9.1 million miles or 0.1 astronomical units) from our planet, and as far as 100 times the Earth-Moon distance (24 million miles or 0.25 astronomical units).
As an Apollo asteroid, 2016 HO3 joins the small but growing list of objects tracked in a solar orbit near Earth. Asteroid 2003 YN107 was discovered by the LINEAR sky survey about a decade ago, when it followed a similar track, but the rock has since departed our neighborhood. Asteroid 2006 RH120 made several distant looping passes of the Earth from April 2006 to September 2007 before ejection. Turns out our Moon does a pretty good job at celestial goal tending, assuring such secondary hopefuls never hang around for long.
Simulations carried out by Mikael Granvik (University of Helsinki, Finland) in 2012 suggest that most TCOs only complete three orbits of the Earth-Moon system before ejection, and only 1% ever impact Earth. (Read Sky & Telescope's September 2015 issue for more info.)
Ideas for a tiny second moon around Earth, dubbed "Lilith," go all the way back to alleged sightings in the 19th century. "Petit's Moon" created a temporary sensation in 1846, until it too proved to be spurious. In modern times, spent boosters from the Chinese Chang'e-2 and Apollo 12 lunar missions were tenoriarilidentified as "asteroids" 2010 QW1 and J002E3. Other objects, such as 3753 Cruithne occupy strange horseshoe-shaped orbits around Earth. Venus also has its own suite of TCOs, such as 2002 VE68.Hunting Temporary Minimoons
A new generation of all sky surveys could swell the ranks of known TCOs. The enormously successful PanSTARRS project, which currently operates with just one of four proposed telescopes, may one day get its full complement for such a dedicated search. A 2014 study suggests that the Subaru telescope could stand a 90% chance of nabbing a potential TCO after only 5 nights of dedicated scanning of the sky. Then there's the Large Synoptic Sky Survey, (LSST) set to see first light in 2022 — they're working on the primary mirrors now (watch the video below).
The discovery of 2016 HO3 spawns far more questions than it answers: Where did it come from? Did the rock spall off the Moon during an impact, or is it merely an asteroid that wandered too close to Earth? Could 2016 HO3 make the candidate list of possible targets for a future crewed mission to an asteroid? Future discoveries will help put 2016 HO3 into context and help reveal its origin.
Astronomers have reconstructed 18-century telescopes to observe sunspots and better understand solar cycles.
Astronomers have been counting sunspots — the most accessible tool they’ve had to measure solar activity — for the past 400 years. In more recent times, technology has advanced, making it easier to pick out smaller sunspots or even measure the magnetic field directly. But some astronomers are now turning back the clock. They’re reconstructing ancient telescopes to observe sunspots as our forebears did to better understand the Sun’s evolution.
Sunspots are irregular shapes on the surface of the sun; the cooler gas, held still by strong magnetic fields, appears dark against the rest of the boiling-hot surface. The more sunspots, the more magnetically active the Sun is. Sunspot observations through the centuries have shown two long-term trends in the Sun’s activity: a possible 100-year cycle and a long-term increase in sunspot number. However, it turns out this second trend isn’t real — it’s due to inconsistencies in sunspot-counting.
A team led by Leif Svalgaard (Stanford)built 18th-century telescopes to count sunspots and record the evolution of the solar cycle in the same way as astronomers from yesteryear. The behavior of the solar cycle is crucial to studying solar dynamics, forecasting space weather, and modeling climate change. Our general understanding of the Sun relies on our knowledge about its past behavior.Early Observations
In the early days of astronomy, sunspots were often ignored or confused for something else. For instance, in 1607, Johannes Kepler wished to observe a predicted transit of Mercury across the Sun’s disk. On the given day, he projected the Sun’s image though a small hole in the roof of his house, a camera obscura, and observed a black spot that he interpreted to be Mercury.
Just a few years later, Galileo and Thomas Harriot, Galileo’s British contemporary, became the first to observe sunspots through telescopes.
Their early telescopes were far from perfect — spherical aberration, caused by the shape of the lens, was a common artifact that blurred images because light didn’t focus at a single point. Aberration coupled with small scopes and corresponding low resolution, made observing and counting sunspots a challenge.
But astronomers were game to try. From 1749 to 1796, German amateur astronomer Johann Casper Staudach observed and drew sunspots using a 3-foot “sky tube.” He drew sunspots for a total of 1,016 days, including days with no observed spots. In 1847, Swiss astronomer Rudolf Wolf started counting and recording the number of sunspots he saw every day.
Wolf used his own observations as well as Staudach’s to create the International Sunspot Number, which described the Sun’s spottedness. But this number, Svalgaard’s team realized, was inaccurate.Counting: A Method to the Madness
When Wolf started counting sunspots, he knew two people could look through the same telescope and see two different things – after all, human vision isn’t consistent and degrades with time. He came up with the idea of not only counting sunspots, but also groups of sunspots to make a more accurate representation of the Sun.
But his definition wasn’t enough: modern instruments have not only better resolution but also are free of aberrations. The improvement in clarity enables modern observers to resolve one big group of sunspots into two or more smaller groups. As of June 1st, having started on January 14th, Svalgaard’s team has produced 160 drawings over 120 days using the telescopes designed after 18th-century scopes. He’s found that on average, modern observes see about three times as many sunspots as what the ancient telescope reproductions show.
That effect is enough to explain the supposed upward trend in sunspot counts seen by other researchers — when Svalgaard accounts for the different telescopes and counting methods, the trend goes away.How to Make an 18th-Century Telescope
John W. Briggs, a member of Svalgaard’s team, reconstructed an 18th-century telescope to observe and draw sunspots the same way Staudach did more than 200 years ago. Briggs used a 30-mm lens of 1-meter focal length and glued it a large steel washer. Then he glued the washer to the end of a cardboard mailing tube decorated with a spiral layer of copper tape. For the eyepiece, he used a brass ocular in fair condition and borrowed a brass draw tube from a 7-inch Clark telescope, built circa 1865, to better focus the image.
Brigg’s replica has a clear aperture (the diameter of its main, light-gathering lens or mirror) of about 20 mm. At such a small aperture and long focal length, spherical aberration becomes less significant.
After Briggs mounted the replica on a light tripod, he projected a 3-inch solar image onto a white sheet of paper clipped to a screen. The larger sunspots were obvious, including the penumbrae, but not the smaller sunspots.
Several other members, who are also part of the team and live in different parts of the country, have made similar reconstructions and observations. “After drawing spots for six months, my expectation is that future results from a variety of telescopes will prove quite similar,” said Briggs.
The ongoing investigations were reported at the 2016 meeting of the Solar Physics Division in Boulder, Colorado. Svalgaard and his team plan to continue the project to add to existing sunspot records and aid in our understanding of the Sun’s evolution.
Friday, June 24
• This is the time of year when the two brightest stars of summer, Arcturus and Vega, are about equally high overhead shortly after dark: Arcturus is toward the southwest, Vega is toward the east.
Arcturus and Vega are 37 and 25 light-years away, respectively. They're examples of the two commonest types of naked-eye stars: a yellow-orange K giant and a white A main-sequence star. They're 150 and 50 times brighter than the Sun — which, combined with their nearness, is why they dominate the evening sky.
Saturday, June 25
• At nightfall, look for the Big Dipper hanging straight down in the northwest. Its bottom two stars, the Pointers, point to the right toward modest Polaris, the handle-end of the Little Dipper.
The rest of the Little Dipper floats straight upward from Polaris — like a helium balloon escaped from some June evening party. Most of it is quite dim; through light pollution, you may only see Polaris and Kochab, the lip of the Little Dipper's bowl, 16° above it.
Sunday, June 26
• Three doubles at the top Scorpius. Mars and Saturn aren't the only telescopic attractions in the south these evenings, even you have heavy light pollution! The head of Scorpius — the near-vertical row of three stars upper right of Antares — stands to Saturn's right by about a fist at arm's length. The top star of the row is Beta (ß) Scorpii or Graffias, a fine double star for telescopes.
Just 1° below it (and a little too faint for the chart here) is the very wide naked-eye pair Omega1 and Omega2 Scorpii, not quite vertical. Binoculars show their slight color difference. Left of Beta by 1.6° is Nu Scorpii, another fine telescopic double. High power in good seeing reveals Nu's brighter component itself to be a close binary, separation 2 arcseconds.
Monday, June 27
• The last-quarter Moon (exact at 2:19 p.m. EDT) rises around 1 a.m. below the Great Square of Pegasus.
Tuesday, June 28
• Arcturus is the brightest star high in the west. Equally bright Vega is similarly high in the east. A third of the way from Arcturus to Vega, look for dim Corona Borealis, the Northern Crown, with its one modestly bright star, Gemma or Alphecca. Two thirds of the way, you'll find the dim Keystone of Hercules.
Wednesday, June 29
• As evening grows late, even the lowest star of the Summer Triangle climbs fairly high in the east. That would be Altair, a good three or four fists at arm's length below or lower right of bright Vega.
Look left of Altair, by hardly more than one fist, for the compact little constellation Delphinus, the Dolphin.
Thursday, June 30
• Vega is the brightest star very high in the east. Barely to its lower left after dark is one of the best-known multiple stars in the sky: 4th-magnitude Epsilon (ε) Lyrae, the Double-Double. It forms one corner of a roughly equilateral triangle with Vega and Zeta (ζ) Lyrae. The triangle is less than 2° on a side, hardly the width of your thumb at arm's length.
Binoculars easily resolve Epsilon, and a 4-inch telescope at 100× or more should resolve each of Epsilon's wide components into a tight pair.
Zeta Lyrae is also a double star for binoculars; much tougher, but easily split with any telescope. Delta (δ) Lyrae, below Zeta, is much wider and easier.
• Mars is stationary; it ceases its retrograde (westward) motion and will begin returning eastward toward Saturn and Antares. It will slingshot between them on August 23rd and 24th.
Friday, July 1
• Is your sky dark enough for you to see the Coma Berenices star cluster naked-eye? Just after the very end of twilight, spot Jupiter in the west. The cluster is above it by 25°, about 2½ fists at arm's length. Its brightest members form an inverted Y. The entire cluster is about 5° wide — a big, dim glow in a truly dark sky. It nearly fills a binocular view.
Saturday, July 2
• If you have a dark enough sky, the Milky Way now forms a magnificent arch across the whole eastern sky after nightfall is complete. It runs all the way from below Cassiopeia in the north-northeast, up and across Cygnus and the Summer Triangle in the east, and down past the spout of the Sagittarius Teapot in the south.
Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.
This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy.
Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or new Jumbo Edition), which shows stars to magnitude 7.6.
Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5, nearly three times as many. The next up, once you know your way around, is the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.
You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger Night Sky Observer's Guide by Kepple and Sanner.
Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). And as Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."This Week's Planet Roundup
Mercury is disappearing deep into the glow of sunrise.
Venus is hidden deep in the bright sunset.
Mars (magnitude –1.5, in Libra) is now only Sirius-bright; it was closest to Earth on May 30th. It's the yellow-orange point shining in the south during and after dusk. Mars shrinks from 17 to 16 arcseconds wide this week, as Earth pulls ahead of it in our faster orbit around the Sun. See our telescopic guide to Mars in the April Sky & Telescope, page 48, or the version online. And set our Mars Profiler for your time and date.
Jupiter (magnitude –1.9, at the hind foot of Leo) shines in the west during and after dusk. It's on the far side of its orbit from us, 34 arcseconds wide, almost the smallest it ever appears.
Saturn (magnitude +0.2, in southern Ophiuchus) glows about 20° east (left) of Mars. To Saturn's lower right by 6° or 7° sparkles Antares, half as bright. Look near the middle of the long Mars-Saturn-Antares triangle for Delta Scorpii (Dschubba). See our telescopic guide to Saturn in the June Sky & Telescope, page 48.
Uranus (magnitude 5.9, in Pisces) is the east before dawn begins.
Neptune (magnitude 7.9, in Aquarius) is higher in the southeast before dawn.
All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.
Eastern Daylight Time (EDT) is Universal Time (UT, UTC, or GMT) minus 4 hours.
“This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours.”
— Neil deGrasse Tyson
Take a trip down the rabbit hole to the weird and weighty world of planet-sized white dwarf stars.
A few weeks back we looked at some of the largest stars known. I hope you've had time and clear skies to make their acquaintance. Today, we proceed in the opposite direction and seek the smallest stars accessible to amateur telescopes: white dwarfs. Unlike the gasbag supergiants, white dwarfs pack their matter tightly, squeezing in a Sun's worth of mass into a fiercely hot sphere only as big as the Earth.
A spoonful of matter taken from anywhere in a supergiant except its compact core would only weigh a fraction of a gram. But that same spoon dipped into a white dwarf would weigh 5.5 tons and require a well-anchored crane to lift!
White dwarfs mark the end of the road for main sequence stars up to 8 times as massive as the Sun. During its life, a star burns through its hydrogen reserves, steadily converting that element to helium in its core. Helium is heavier than hydrogen; as it accumulates, the core contracts and grows hot enough to burn helium into carbon. Carbon combines with helium to make oxygen.
As the star transitions through phases of hydrogen and helium burning, it expands into a red giant, then puffs away its outer atmosphere, exposing a tiny core of carbon and oxygen. Because the star lacks the mass — and the heat and pressure that mass brings to bear — burning halts at oxygen. Without a "fire in its belly" to counteract the unrelenting force of gravity, the core is crushed into a planet-sized sphere with a temperature of over 180,000° F (100,000° C). A white dwarf is born!
The star might continue to crush itself into an even smaller object, but electrons in the carbon and oxygen atoms move to higher orbits and pick up speed during the contraction, resisting a potential implosion. It's called electron degeneracy pressure, and white dwarfs are said to be made of degenerate matter.
Often, the star's former outer layers glow in the copious ultraviolet light streaming from the dwarf, creating a colorful and jewel-like planetary nebula. The planetary expands and fades from view over a period of 20,000 to 50,000 years, leaving only a tiny, white-hot glowing ember that steadily grows cooler until it fades to become a black dwarf. This will almost certainly be the fate of our Sun some 6 billion years from now when it embarks upon a life of electron degeneracy. No need to go looking for any black dwarfs just yet. Since it takes something like a trillion years for a white dwarf to go black, our universe is far too young to have created its first.
White dwarfs may be white and hot, but their small size means that nearly all are faint. But lucky for us, not too faint. The brightest and most familiar is Sirius B at magnitude +8.5. Even at its maximum separation of 11.5″ in 2025, this dwarf's a tough nut because of the overwhelming glare of Sirius itself. Likewise for Procyon B, which shines at magnitude +10.7 but hides in the glow of its primary star only 4.3″ away.
Omicron2 Eridani B at magnitude +9.5, best viewed in the fall and winter months, forms an attractive double with a red dwarf star. It's probably the only white dwarf most amateurs have seen outside of several faint ones occasionally visible in the veiled centers of planetary nebulae.
Let's see if we can rectify that and add a few more of these exotic stars to your treasure chest. I've included charts and information below to help you find eight white dwarfs currently visible in the summer sky. They range in magnitude from about +11.5 to +12.5, making them all fairly easy to spot even in a 6-inch scope under dark skies.
If you need more, download Willem Luyten's White Dwarf Atlas which lists 96 white dwarfs and includes a photo for each. When using the atlas, be sure to precess the given epoch 1950.0 coordinates to 2000.0 using this handy coordinate calculator.Van Maanen's Star
Van Maanen's Star is the most familiar dwarf after Sirius B and Omicron Eridani B and the closest solitary white dwarf to Earth at 14.1 light years. Discovered by Adrian Van Maanen in 1917 in Pisces, it has a magnitude of +12.4 and a high proper motion of 3″ per year. Currently a morning object in Pisces.Stein 2051
Located in Camelopardalis, Stein 2051 forms a pretty double star (~7″ separation) with an 11th-magnitude red dwarf. Bright, easy to spot at magnitude +12.4. Currently a morning object in the northeastern sky before dawn. Located just 18 light years from Earth.LP 145-141
A bright +11.5 solitary white dwarf and one of the best for southern skywatchers. Located 15 light years distant in the constellation Musca. Well-placed during evening hours.L1409-4 BD-7:3632 Grw+70:5824 LDS 678A W 1346
Several thousands of amateur astronomers flocked to the 2016 Northeast Astronomy Forum, held every year in Suffern, New York, to see some of the hottest new telescopes, mounts, cameras, eyepieces, and other astronomy equipment at one of the world's largest astro trade shows.
Former S&T editor Dennis di Cicco interviewed several vendors about their newest products.
Browse vendors below and click to watch these in-depth conversations and find full details on new product lines and featured equipment.Video Interviews on Astronomy Equipment
Dennis di Cicco talks with several members of the Celestron staff who demonstrate the latest version of the Evolution series of Schmidt-Cassegrain telescopes and the new Power Tank Lithium battery that provides advanced performance in a small package. Also discussed is the brand new Inspire line of refractors which includes features never before found on entry-level telescopes.
iOptron’s Roger Rivers tells Dennis di Cicco about the advanced features offered on the company’s extensive line of altazimuth and equatorial telescope mounts, including the new AZ Mount Pro with a built-in rechargeable battery. The interview ends with an introduction to several members of iOptron design team in China who attended NEAF this year.
See additional videos from the 2016 Northeast Astronomy Forum held in Suffern, New York.