Innholdsfortegnelse for May/June 2017 i Australian Sky & Telescope

NASA’S MARS SCIENCE LABORATORY, a.k.a. the Curiosity rover, is the most complex machine ever sent beyond Earth. Since its 2012 daredevil landing inside a broad crater called Gale, it has ventured 15 kilometres across the crater’s interior, trundling 17 cameras, several spectrometers, a suite of weather sensors and two miniature laboratories along as it investigates whether Mars was ever habitable. A habitable environment needs three things: liquid water to facilitate chemical reactions, sources of energy and organic (that is, carbon-bearing) material, and long-term stability — time in which chemistry can take place in that water. It’s better if the water is not so acidic or saline that it inhibits chemical reactions, and if a thick atmosphere or magnetic field (or both) shields the surface from harmful radiation. Geochemists think the…

Is the Milky Way’s history ‘typical’? We have to look at other galaxies to answer that question. Simulations predict that deep (long-exposure) observations should detect stellar streams in the outskirts of almost all nearby galaxies. But such features are extremely faint and difficult to find. Few were spotted until 1997, when astrophotographer David Malin used enhancement techniques on photographic plates to image structures around the spiral galaxies M83 and M104. I was inspired by his pioneering work and began observing other nearby spirals using professional telescopes — but without success. By chance, years later, I stumbled upon some deep galaxy images that astrophotographer R. Jay GaBany had posted on his website. I invited him to join me. Within a couple of years, we had detected a wide assortment of giant…

Jupiter is this month’s target, for three reasons. First, it’s the most rewarding planet to observe with binoculars. Even at 7x, the King of Planets is a disk rather than a point of light. But the real show is the four Galilean moons — Io, Europa, Ganymede and Callisto — visible to either side (assuming they’re not hidden behind the planet). At 15x, the major cloud belts can be seen under good conditions. Once at a star party, I aimed my tripod-mounted 15x70s at Jupiter. After looking for a long time, a friend remarked, “With these, you hardly need a telescope!” Second, it’s no exaggeration to say that observing Jupiter with binoculars is the reason I write about astronomy. Back in 2007, I picked up a stargazing guide on a…

As I remarked in the previous issue, the short-period comet 41P/ Tuttle-Giacobini-Kresak will arrive in the constellation Hercules as April closes and May begins, becoming accessible to observers at mid-southern latitudes in the northern predawn sky at an expected magnitude of around 7.5–8. 41P will move quickly southward as it pulls away from its April 14 perihelion passage at 1.05 a.u. from the Sun and its passage by Earth at just 0.15 a.u. on April 5. It will traverse Hercules and Ophiuchus during May and June, ending the latter month in Serpens Cauda. During this period, it is expected to fade as it moves away from both Sun and Earth, declining in brightness to around magnitude 10 by early June and to around 12–13 by the end of that month.…

WE SEE OUR GALAXY, the Milky Way, as a band of light stretching across the sky. There’s a ghostly aspect to it; faint streamers of gas and dust extend far above and below the galactic plane, reaching the galactic pole. This galactic cirrus — twisted clouds of interstellar dust particles at high galactic latitudes first observed in the far infrared in 1983–84 by the Infrared Astronomy Satellite (IRAS) — glows in the dim red region of the spectrum. But the dust also reflects blue light from countless millions of stars, as shown by amateur astronomer Steve Mandel in 2004. Mandel noticed the subtle blue glow of the spooky dust tendrils associated with M81 and M82 and captured it in images. These images, which formed the basis of his Unexplored Nebula…

OVER THE WEEKEND of June 24–25, astro enthusiasts will gather at Byron Bay for Star Stuff, billed as a ‘festival of the cosmos’. There’ll be telescope viewing, photography workshops and presentations by experts of astrophysics and astrophotography, including Prof. Fred Watson, Dr David Malin, and photographers Dylan O’Donnell and Mark Gee. Full details at starstuff.com.au The Centre of Excellence for All-Sky Astrophysics will once again host the Sydney Astrofest, on July 1 at the University of Sydney. A family friendly program of free indoor and outdoor activities will include night-sky telescope viewing, lectures (including special ones for kids), planetarium shows, demonstrations and prizes. Full details can be found at caastro.org/event/2017-sydastrofest17 The CWAS David Malin Awards for astrophotography is on again, with a prize pool of $10,000 in Canon estore vouchers…

THE LAST PREHISTORIC standing stone circle was erected in the British Isles thousands of years ago. So why would I, an amateur astronomer, want to build one now? For that’s what I did recently with the support of fellow members of my local astronomical society. One of our club’s goals is to help anyone interested in gaining a better understanding of the universe we live in. Why not start with the closest star to Earth, our very own Sun? What better way to introduce young people to astronomy than to show them firsthand how some ancient peoples used the Sun as a calendar? Three years ago our society received a gift of 14 hectares of flat terrain. With its dark skies and easy access, the site is ideal for use…

Void ‘repels’ Milky Way’s galaxy group ASTRONOMERS HAVE DISCOVERED a giant cosmic void that explains why our Local Group of galaxies is moving through the universe as fast as it is. The Local Group lies in a filament of a much larger cosmic structure. The galaxy clusters in this cosmic web don’t stay still but rather gravitate (literally) toward the largest members. Our Local Group is moving toward what’s called the Great Attractor, a dense collection in the vicinity of the Centaurus, Norma and Hydra clusters about 160 million light-years away. Beyond that and about four times farther away lies another, equally influential attractor called the Shapley Supercluster. But it turns out that there’s another player. Using the Cosmicflows-2 catalogue of galaxies, Yehuda Hoffman (Hebrew University, Israel) and colleagues have…

As an aging star loses mass, planets that orbited it stably for billions of years will drift outward and begin to interfere with each other. Chaos will grow. IF SOMEONE HAD TOLD ME 20 years ago that I, an amateur astronomer, would someday be on my roof watching the destruction of a small planet orbiting a 17th-magnitude star, I would have said they were nuts. Yet I and other amateur astronomers are now doing just that, and more. WD1145+017, or WD 1145 to its friends, is an obscure white dwarf star 570 light-years away in Virgo near the Leo border. It is pulling apart, grinding up and devouring one or more of its planets as we watch. We are monitoring fast-changing clumps and streams of orbiting wreckage as they cross…

DISK AND RING STRUCTURES are abundant on every scale throughout the universe, from rings around planets to protoplanetary disks to debris disks to black-hole accretion disks to gas-rich galaxies. As different as these objects are, they all take their shape for the same reason — conservation of angular momentum in a rotating system of stuff that can’t get rid of it. Ringed planets must be abundant everywhere; all four gas giants in our Solar System have at least slight rings. But the wide, dense rings of Saturn are unique among anything we can see. Saturn has crept far south in recent years, in its 29.5-year circuit around the Sun and the zodiac. In 2017 it glows northwest of the Sagittarius ‘Teapot,’ not far from the Lagoon Nebula, at about declination…

Which is by far the longest constellation of the zodiac? As you may know, it’s the lady of the zodiac, Virgo. The Sun travels 44° through Virgo, thus almost 1/8 rather than1/12 of the zodiac falls in Virgo. The Sun is within the constellation’s bounds in early spring. In May, however, Virgo is well-placed for observation in the north, as shown in our all-sky map on pages 42–43. Many deep sky observers prize Virgo for just one thing: the vast Virgo Galaxy Cluster, composed of dozens of galaxies visible through small amateur telescopes and hundreds to thousands visible through larger ones. I want to make a suggestion about observing the galaxies of Virgo and of its neighbouring constellations on autumn evenings. But first I want to speak in praise of…

This column visited the central part of Hydra three years ago; this time I’ll describe double stars from a more easterly end of this very long constellation. First up is Beta Hydrae, HJ 4478 , the end-point of the previous column. Discovered by John Herschel in 1834, this long-period binary has now become much closer than the easy 2› separation of the 1830s. In 1961 separation was a whisker under 1.0› when Ernst Hartung reported that it could just be separated with 15 cm aperture. By the late 1990s it was at 0.7›, and with 18cm aperture showed an uneven figure-8 shape. Returning to Beta in 2015 with my current favourite double star scope, a 210-mm refractor, I found the image similar to the one I’d seen with 18 cm…

As stone lions often flank the stairways to palaces and museums, so Leo watches over the grand entrance to the land of the galaxies. — Leland S. Copeland, Sky & Telescope, May 1942 Leo leads a procession of springtime constellations greatly renowned for the teeming swarms of stars that we call galaxies. Leo itself harbours 809 galaxies from the New General Catalogue (NGC), five of them previously listed in Charles Messier’s catalogue. For this foray into the night sky, we’re going to turn our gaze toward three of those bearing Messier designations and assorted NGC escorts. The members of our Messier galaxy trio were discovered with a 75-mm refractor by Charles Messier’s colleague, Pierre Méchain. Méchain found the first two, Messier 95 and Messier 96, on May 20, 1781. He…

SOME OF THE MOST DRAMATIC VIEWS of celestial objects seen today have been created using the technique of narrowband imaging. Instead of combining individual frames taken through red, green and blue filters, photographers employ filters that isolate the wavelengths of light produced by ionised gases in emission nebulae. False-colour photographs assembled from images taken through these filters are much more colourful than natural-colour images. Narrowband imaging also enables urban imagers to pursue deep sky astrophotography in light-polluted settings. The extremely narrow passbands of emission-line filters block most of the wavelengths produced by streetlights and other artificial illumination (as well as moonlight). This enables you to reveal ionised gases that permeate the Milky Way and other galaxies from even badly light-polluted areas. It’s no wonder that narrowband imaging has become so…

HELLO, MY NAME IS DAVID, and I have a Venus problem. For decades I’ve had an unhealthy compulsion. I’ve been doing the same thing over and over again and expecting a different result. And there’s a whole community of us who share this questionable obsession. The title of this column is the perennial answer to where NASA will send its next interplanetary spacecraft. The US hasn’t launched to Venus since 1989. That mission, Magellan, revealed our sister planet to be an incredibly beautiful and geologically interesting place, and it raised many new questions: What’s in that thick atmosphere? Was there an ocean, and for how long? Could life have gotten started? In the wake of Magellan, we thought these and other burning questions would logically lead to new NASA spacecraft…

We first met T Centauri four years ago, but this unusual and easy-to-observe star demands closer attention. T Cen is a pulsating giant whose exact classification has proved tricky. Despite differing sources and opinions, 120 years of light curve data says that it is an RVb star. ‘RV’ stars, after RV Tauri, show alternating deep and shallow pulsations that can vary in depth, even swap around, with amplitudes reaching 3 to 4 magnitudes, and periods between adjacent primary minima in the range of 30 to 150 days. ‘RVb’ means that the mean magnitude itself varies over time. While it’s reasonably well established that the RV stars represent a transitional stage between the red giant and the planetary nebula stage, no one really knows why these stars vary in just this…

Nearly all lunar craters formed by impact, but some have peculiarities that can’t be explained as simply punching a hole in the Moon’s surface. For example, concentric craters (CCs) contain circular rings or ridges, like a doughnut snuggled onto their inner walls and floors. The most famous of these, and one of the biggest, is 15-km-wide Hesiodus A , on the southern shore of Mare Nubium. You can spot its inner ring even through small telescopes using medium- to high-magnification. A few CCs have been known since at least the 1950s, but not until 1978 was a catalogue published, by me, listing 51 of them. I found that these craters average 8 km in diameter and that the inner ring is about half as wide. Only a handful could be…

What We Like Outstanding optical performance Robust mechanical construction Compact design allows for easy storage and travel What We Don’t Like Relatively heavy instrument for its aperture Imaging setups require multiple adapters TAKAHASHI, the Japanese firm long known for crafting some of the world’s finest telescopes and astrographs, has upped the ante for wide-field, deep sky astrophotography. The company’s new FSQ-130ED Super APO astrograph is the big brother to the FSQ-106ED and the latest addition to a line of astrographs that have achieved legendary status among astrophotographers. Chances are better than not that those spectacular wide-field celestial vistas you’ve seen in magazines and on the web were made with one of Takahashi’s FSQ telescopes. Compared to its smaller sibling, the FSQ-130ED adds about 2.5-cm of aperture and 12 cm of…

WE ALL KNOW the importance of avoiding light pollution. But even if you shield yourself from every light around you there’s still one enormous source of stray illumination: the sky full of stars! Most of us don’t think of that as a problem, but if you’re trying to tease out the finer details of a distant galaxy, every stray photon that’s not part of your target becomes a contrast-reducing part of the general background. Fortunately Tom Osypowski, Howard Banich, and Chuck Dethloff have come up with the perfect solution. Tom first saw the idea at a star party back in 1985. Someone had glued two slabs of Styrofoam to the top of his scope, making a tent that shielded the eyepiece from overhead light. Tom says, “My own take was…

LUNAR LANDSCAPE Clay Reid Our nearest neighbour presents endless photographic opportunities. For this panorama, Clay used a Vixen ED102S scope, Takahashi 18-mm LE eyepiece, VariMax eyepiece projection unit, Canon EOS 600D camera (ISO 200, 0.25s exposure) on a Sky-Watcher HEQ5 mount. ASTRONAUTS ABOVE Glenn Krause The International Space Station zoomed through Canberra’s skies on February 21, and Glenn was ready to capture the sight from Mt Ainslee. He used a Nikon D5100 DSLR with an 18-55mm Nikon lens (18-mm focal length at f/8) for sixteen, 13-second exposures, using a hand-held remote. SPREADING WINGS Leigh Westerland Leigh took this image of the International Space Station from his backyard in Geelong. He hand-guided a 20-cm Dobsonian and captured the image (one of a series) with a ZWO ASI120 video camera. PIPP and…