Innholdsfortegnelse for Oct 2016 i Australian Sky & Telescope

How do you spot something that’s invisible? Simple, use something else that’s invisible to help you. That’s what astronomers are doing in their quest to understand the nature of dark energy and dark matter — both of them so far invisible to us — by using the invisible force of gravity to map the distorting effects they have on the universe’s ordinary matter in the form of stars and galaxies. It’s a technique called ‘weak lensing’ (see page 14), and it’s being used to answer some of the most fundamental questions about the origin and evolution of the cosmos. Closer to home, within our own Milky Way, are a group of planetary nebulae that are not invisible but quite hard to spot. And it is their challenging observational nature, of…

Astronomers have made the first high-resolution image of a cometary belt around the young star HR 8799. The disk, a region comparable to our Solar System’s Kuiper Belt, lies outside the orbits of the star’s four known planets. But in imaging the belt, Mark Booth (Pontifical Catholic University of Chile) and colleagues discovered signs of a fifth planet. Previous observations found that the disk extended from roughly 100 to 310 astronomical units. Astronomers had also found evidence of a halo of small dust grains. But it was hard to tell the difference between the belt and the grains. Using ALMA to pick up emission from the disk’s dust, Booth’s team found that the inner edge lies between 133 and 166 a.u. That’s too far out to have been carved by…

Astronomers have found a pair of hypervelocity stars in our galaxy’s halo, racing at twice the Sun’s speed. The stars, SDSS J121150.27+143716.2 and its dimmer mate, aren’t the first hypervelocity binary found. But they’re the first that’s proven so difficult to explain. The Milky Way’s central black hole can’t have slingshotted them out — even if the trajectory matched that scenario, the encounter would have disrupted the binary. Nor could the explosive death of a third stellar companion have done it, explain Péter Németh (Friedrich-Alexander University Erlangen-Nuremberg, Germany) and colleagues. If the stars are bound to the galaxy, then the dark matter halo within their orbit must contain at least 3 trillion Suns’ worth of mass — an estimate that’s larger than previous measurements.…

As light traverses the universe, spacetime’s expansion stretches the wavelength. For relatively nearby objects, this is most easily measured by the redward shift of emission (or absorption) lines in an object’s spectrum. But measuring spectroscopic redshifts becomes impractical for millions of faint, faraway galaxies — collecting a spectrum requires a bright target and lots of time. So astronomers resort to photometric redshifts: rather than gathering a galaxy’s light into the narrow buckets that make up a spectrum, filters split light into broader buckets. Then astronomers compare this rough approximation of a spectrum to galaxy templates until they find the best match. Although photometric redshifts aren’t as precise as spectroscopic measurements, they work well for large samples of faint objects.…

German-American astronomer Rudolph Minkowski fled Hitler’s Germany to join the staff of the Mount Wilson Observatory in 1935. His interests were many, and he’s well known for his spectroscopic studies of supernovae. Less familiar are his studies of gaseous nebulae. In his early years at Mount Wilson, he conducted a survey to find new planetary nebulae (PNe) using an objective prism mounted on the 10-inch Cooke wide-angle camera. He later obtained slit spectroscopy of the suspected planetaries with the 60-inch and 100-inch telescopes. Minkowski’s work more than doubled the number of planetary nebulae known at the time. In three papers published in the Publications of the Astronomical Society of the Pacific entitled “New Emission Nebulae” in 1946, 1947 and 1948, he gave us a catalogue of nearly 200 real or…

WHEN Early September 10pm Late September 9pm Early October 8pm Late October Dusk These are standard times. Add 1 hour for daylight savings. HOW Go outside within an hour or so of a time listed above. Hold the map out in front of you and turn it around so the label for the direction you’re facing (such as west or northeast) is right-side up. The curved edge represents the horizon, and the stars above it on the map now match the stars in front of you in the sky. The centre of the map is the zenith, the point in the sky directly overhead. FOR EXAMPLE: Turn the map around so the label “Facing SW” is right-side up. About a third of the way from there to the map’s centre…

For Southern Hemisphere sky watchers, the Orionids is one of the best meteor showers of the year. Unfortunately, in 2016 the maximum on the night of October 21/22 will coincide with the last quarter of the Moon, which will be quite close to the radiant. This will affect the ZHR (zenithal hourly rate), which is the number of meteors visible under perfect conditions. The good news is the radiant will be at a useful elevation from most locations, and so you should be able to see some activity. No increased organic activity is predicted for 2016, with rates of around 6 to 8 per hour on the morning of the 21st/22nd. Orionid meteors are often white and blue in colour, are of medium speed and often leave persistent trains that…

Without a doubt, the shining jewel of the constellation Scutum is the open cluster Messier 11, also known as the Wild Duck Cluster. German astronomer Gottfried Kirch discovered it on September 1, 1681. At first he was uncertain whether he was seeing a comet or a “nebulous star,” but he dismissed the possibility of it being a comet when the object’s position remained unchanged during succeeding nights. More than half a century later, British cleric and astronomer William Derham published his observations of nebulous stars, which he called “whitish Areae, like a Collection of Misty Vapours: whence they have their Name.” In the same memoir, Derham became the first observer to report that he found Kirch’s object to be a cluster of stars. Perhaps the historical description that resonates most…

This is the final of three articles on 60 of the best southern star clusters, nebulae and galaxies. Our first article (July 2016 issue) described 10 open star clusters and 10 globular star clusters, while the second article (Aug/Sep 2016 issue) covered 10 nebulae and 10 planetary nebulae. In this article, we’ll cover 20 galaxies south of declination –20. The Catalogue of Principal Galaxies (G. Paturel et al., 1989) lists 177 galaxies south of –20 and brighter than magnitude 12. The 20 on our list are easy to see, and arguably the best of these southern galactic gems. James Dunlop, a Scottish astronomer, discovered 18 of the 20 from Australia; the other two (NGC 253 and NGC 1097) were discovered from England by Caroline Herschel and her brother William. Dunlop…

I have seen the future, and it is fast. It’s also vast — 80 cm in diameter, to be precise, and just over 210 cm high at the eyepiece. Modern telescope making seems to be a rush toward ever greater apertures at ever shorter focal lengths. ATMer Phill Oltmann has pushed those parameters about as far as I’ve ever seen. Phill decided to see how large and fast he could go. He had already made a 50-cm f/4 and realised that if he used the same tools to generate the same curve, he could make an 80-cm mirror at f/2.5. He ordered a blank from Newport Glass and had them pre-generate the rough curve, removing nearly 20 mm of glass from the 6.25-cm blank’s centre. He began grinding with 60-grit…

ON MAY 12–13, AMATEURS AND professionals interested in supporting NASA’s Juno mission met in Nice, France, for a workshop dedicated to projects and techniques related to observing Jupiter. The spacecraft arrived at the giant planet on July 4. Although Juno will image Jupiter at very high resolution, especially in the polar regions, it lacks the ability to create global portraits. So it falls to Earth-based observers to watch regions out of view from the probe and to acquire the large-scale views that provide context for the spacecraft’s small-scale scrutiny. Highest on the ‘to do’ list for the months ahead is to sustain the ongoing ground-based survey of Jupiter, so lots of discussion focused on the necessary equipment, imaging and processing tools and techniques needed for that task. For example, more…

European and Russian officials have postponed the launch of the European Space Agency’s first Martian rover for two years. The first ExoMars mission, comprising the Trace Gas Orbiter and the Schiaparelli lander, left Earth as planned in March. The second phase, a rover, was scheduled to follow in 2018. But because the same team was working on both phases, holding to the 2018 launch date would have forced the team to build the final space-bound rover before completing the prototype and finishing tests — clearly unacceptable.…

AKuiper Belt object discovered nearly a decade ago turns out to be much darker — and thus larger — than thought. It’s also an especially slow spinner. Planetary scientists typically guesstimate the diameter of any newly discovered Solar System object using its magnitude. But that requires assumptions about its surface reflectivity, or albedo. To learn more about the Kuiper Belt object 2007 OR10, András Pál (Konkoly Observatory, Hungary) and others used data from NASA’s repurposed Kepler space telescope along with archival observations from ESA’s Herschel Space Observatory. By combining the object’s radiated heat with its visible brightness and its rotational period, Pál explains, “one can unambiguously obtain the size of the object and the surface albedo as well.” As the team explains in the May Astronomical Journal, the object is…

OFF-AXIS GUIDER SBIG introduces the STX Guider (US$999). This self-guiding accessory attaches to the front of the FW7-STX filter wheel, enabling you to choose faint guide stars by intercepting light from the optical path before it passes through the imaging filters. The unit incorporates a 0.7x telecompressor lens that focuses light onto a KAI-0340 CCD guide sensor with 7.4-micron pixels in a 640×480 array. The STX Guider also permits you to adjust the pick-off mirror and focus position independently of the imaging camera and lock them in place. Requires an additional ¾-inch of back focus in your telescope’s optical train. sbig.com and local dealers MULTI-MOUNT Orion Telescopes & Binoculars has released the Sirius Pro AZ/EQ-G Computerised Go To Telescope Mount (US$1,499). This multi-purpose mount is equally useful as a German…

“The realm of fairy-story is wide and deep and high and filled with many things: all manner of beasts and birds are found there; shoreless seas and stars uncounted; beauty that is an enchantment, and an ever-present peril; both joy and sorrow as sharp as swords. In that realm a man may, perhaps, count himself fortunate to have wandered, but its very richness and strangeness tie the tongue of a traveller who would report them.” — J. R. R. Tolkien, ‘On Fairy-Stories’ This issue we continue our journey down the Heavenly River, the Milky Way, and find, as in the quote from Tolkien below, that the “richness and strangeness” of this realm in the sky are so great that they defy our attempts to describe them. The fantastic Milky Way…

Microscopium is one of the modern constellations, invented in 1752 by Lacaille, and representing another of the laboratory instruments. Although it has no stars brighter than 5th magnitude, it does have a variety of double stars that show well through modest telescopes. To begin, the fine uneven pair JC 18 is in south-eastern Microscopium, nearly 7 degrees North from Alpha Indi (mag. 3.1). JC 18 has shown no certain change since discovery in 1846 by Captain Jacob, about whom I wrote a brief biography in the January 2014 issue of Australian Sky & Telescope. It’s an easy object that 8 cm aperture should show. I found it a pleasing sight with 18 cm at 100x, the field moderately starry and with an 11th-magnitude field star 108" southeast. JC 18 could…

At the 1970 Christmas meeting of the British Astronomical Association (BAA), I had a chance conversation with the (now late) Patrick Moore regarding the colour of Uranus as seen through a telescope. He was adamant that its colour is green — whereas I, then as now, see it displaying a diverse range of blues. The various astronomy books I later consulted for definitive Uranian ‘facts’ proved as disparate as Moore and I had been — though they confidently stated that any amateur observation of Uranus was pointless (save for brightness estimates) because of the planet’s very small apparent size and the presumed inadequacy of amateur equipment. This planet had never been subject to the kind of unified, long-term amateur observation that can complement more detailed but time-limited professional work. For…

When was the last time you visited a planetarium? If it’s more than about 20 years ago, you’ll be in for a pleasant surprise the next time your drop in. Gone are the days (for the most part) of having a strange projector contraption in the middle of the circular room, simulating stars by emitting light through tiny holes, and with a few slide projectors aiming crude images onto the dome above. These days, planetaria are more like 360-degree IMAX theatres, able to display full-colour, full-dome, full-motion video presentations as well as computerised night sky demonstrations. Most capital cities, and some of the larger regional centres across Australia and New Zealand have a planetarium, large or small, and there are even mobile planetaria that can come to you for your…

More than anything else, two books have shaped the arc of my astronomical life: Starlight Nights and Norton’s Star Atlas. Leslie Peltier’s Starlight Nights, which I bought in 1965 when it was first published, showed a 15-year-old budding astronomer how much one could do with a simple telescope and a willingness to persist. I had already read biographies of the greats — Galileo, Brahe, Kepler. The life of George Ellery Hale, including his heroic efforts to build ever bigger telescopes, was fascinating. But all these lives were full of stress and turmoil. Peltier’s story was far more appealing to a teenager bitten by the stargazing bug. Look at the stars as often as you can. Never lose the sense of wonder and wonderful things will happen. Observing variable stars became…

Last year, ASASSN-15lh gained fame as the most luminous supernova ever discovered. Now almost a year Later and against all odds, the supernova has rebrightened. Subo Dong (Peking University, China) and colleagues discovered ASASSN-15lh on June 14, 2015, using the All-Sky Automated Survey for Supernovae (ASASSN). Its peak power was more than twice that of any previously known stellar explosion. Usually, much of a supernova’s initial glow actually comes from the decay of radioactive nickel, created in abundance near the core. What’s weird about ASASSN-15lh and a few others like it is that they’re so bright, they’d need an awful lot of nickel to explain their glow. Then, three months after it began fading, the supernova changed its mind. Over some 40 days, its ultraviolet radiation increased fivefold before plateauing…

Nothing is what it seems. That’s often the case in daily life. But it’s also true in the universe at large. Take a long-exposure photo of remote galaxies, and you’ll find that none of them are what they appear to be. First of all, we see faraway galaxies as much younger than they really are right now — their light took billions of years to reach us. We also see them as much redder than they used to be. That’s because, during the long trip to Earth, the universe’s expansion stretched the galaxies’ emitted light to longer wavelengths. It’s as though we look at an old greybeard and see a red-haired schoolboy instead. But that’s not all. Even the observed shape of a distant galaxy isn’t real: it doesn’t reflect…

A noted extraterrestrial sage once advised his pupil, “You must unlearn what you have learned.” I think about this all the time while stargazing. Knowing the constellations, the celestial coordinate system, and all the other tips and tricks is great until you get on target. But as soon as you’re there, you have to actively force that geocentric perspective out of your head to grasp what’s really going on. Take NGC 6934, a globular cluster in Delphinus, the Dolphin. It’s about 10 ° east of Altair, and just a little bit south of the Dolphin pattern on the southeast border of the Milky Way. Like most globulars, NGC 6934 looks like a fuzzy star through binoculars. But to go there in your mind — to see things as they are,…

The innermost planet, Mercury, is not well placed for viewing in October, being lost in the dawn light out to the east. By the end of the month it will have moved along in its orbit to the point called superior conjunction, which means it will be on the opposite side of the Sun from us. Mercury will reappear in our evening sky in November. Venus, on the other hand, is perfectly placed for observation in the western sky from twilight onwards. Shining at a brilliant magnitude –3.9, the planet will begin the month amongst the stars of Libra, slowly shifting as the weeks pass until it reaches Scorpius and then Ophiuchus. At this point, on October 28, it will form up in a line with the star Antares to…

Variable star observers don’t work alone. Well, we do, but what I mean is that we connect with astronomers all over the world. The American Association of Variable Star Observers (AAVSO) is the primary mediator of this connection, and Andrew Pearce of Western Australia is the new leader of the long-period variable (LPV) section. (He had a ‘good idea’ at a meeting and was promptly drafted to implement it!) The section’s purpose is to encourage the observation of LPVs and to serve as a hub for both observers and researchers. ‘LPV’ is an umbrella term covering several sub-types, including semi-regular and Mira-type stars. This month’s target is the semi-regular T Ceti, not too far away in the sky from Mira itself (Omicron Ceti), its own class prototype. T Ceti has…

On March 10th, NASA’s Mars Reconnaissance Orbiter (MRO) completed 10 years in orbit around Mars. That’s not bad for a spacecraft that had a primary mission lifetime of two years. Among its six main scientific instruments, all of which are still working, the standout has been HiRISE, the High Resolution Imaging Science Experiment. This amazing telescopic camera can spot features as small as a picnic table. Combined with imaging spectroscopy, which determines the make-up of surface materials, HiRISE has illustrated the stories of countless, highly varied Martian landscapes. And, crucially, its great longevity has allowed us to see many subtle — and a few dramatic — ways in which those landscapes change over time. Whole new aspects of Mars are revealed when we see the planet with this clarity and…

Mt Stromlo Observatory Astronomy Nights Monthly Public observing nights, courtesy of Mt Stromlo Observatory and the Canberra Astronomical Society mtstromlotour.eventbrite.com.au AstroLight 2016 September 10 Astronomy and Light Festival at Scienceworks Museum, Melbourne astrolightvic.wordpress.com Perth Observatory Open Day September 24 Telescope and dome tours, solar viewing, historical displays, robotic telescope, kids’ activities, live music perthobservatory.com.au Snake Valley Astro Camp September 29 – October 3 Bi-annual astronomy camp and star party under the dark skies of Snake Valley, Victoria snakevalleyastrocamps.org Siding Spring Open Day October 1 Australia’s largest optical observatory throws open its doors to the public. starfest.org.au StarFest 2016 October 1–2 A weekend of activity at Coonbarabran during the Festival of the Stars. starfest.org.au VicSouth Desert Spring Star Party 2016 October 28 – November 1 Annual star party hosted by the…