Innholdsfortegnelse for July 2017 i Australian Sky & Telescope

IT’S A SPECTACULAR SUNSET, with hues ranging from subtle pink and pearl to flaming orange and gold. Venus shines high in the west; Earth’s shadow creeps up in the east. Low, thorny vegetation makes it hard to wander around. And dangerous, too — there are scorpions here. I’m in the Great Karoo, a vast semi-arid region, some five hundred kilometres northeast of Cape Town. It’s incredibly quiet. Hardly anyone lives here; the nearest small town, Carnarvon, is roughly one hundred kilometres away. Still, there’s ample sign of human activity. Silhouetted against the colourful clouds are the dishes of the South African MeerKAT radio telescope array, which is still very much under construction during my visit in late November 2016. “By the end of 2017, all 64 MeerKAT antennae will hopefully…

This mission didn’t end up the way the European Space Agency conceived it in the early 1990s. The original plan called for a spacecraft able to return a sample of comet nucleus. Then it became a mission with two landers (NASA’s Champollion and ESA’s RoLand) before morphing to the orbiter-lander configuration finally built by ESA. Even the original target, a comet named 46P/Wirtanen, had to be changed. The failure of an Ariane V rocket just one month prior to Rosetta’s planned January 2003 launch caused a year-long postponement. That delay put a rendezvous with Comet Wirtanen out of reach. So the team scrambled to find another target that was scientifically interesting, similarly sized (Philae had been designed specifically for the mass of Comet Wirtanen), and in an orbit that could…

Like a lot of stargazers, I often go observing to escape the hassles of life. Serpens Caput, the head of the celestial snake, is a pretty good getaway spot, with a variety of things to see and do. I like to start with the wide, not-quite-a-triangle formed by Beta (β), Gamma (γ), Iota (ι) and Kappa (κ) Serpentis. Most atlases use this group as the ‘head’ of the constellation. That artistic decision is fitting, because the various stars of Tau (τ) Serpentis form a fang-shaped asterism 5° long that points west. The chains of stars, culminating in bright Tau1 Serpentis, even curve like a fang. If the Tau stars form the serpent’s fang, the group of bright stars running southwest from Gamma to Delta (δ) Serpentis can be seen as…

As we move into July, the bright periodic comets which graced our skies earlier in the year have now faded to mere shades of their former selves. Nevertheless, another relatively bright object of short period (due to reach perihelion at 1.59 a.u.on June 30) will be well placed for southern observers in Scorpius during July. Despite its position within a rich region of the Milky Way band, the comet should be a relatively easy object for small- and medium-size telescopes, as it is expected to reach its maximum brightness this month, with some forecasts placing it at around magnitude 10. The comet in question is 71P/Clark. This object is of special interest for southerners as it was discovered by Michael Clark of Mt John Observatory in New Zealand on June…

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EVER SINCE NASA’S Dawn spacecraft reached asteroid 1 Ceres in early 2015, mission scientists have been fixated on bright patches inside the 92-km-wide crater Occator (above). The spots, forming a bright area called Cerealia Facula at Occator’s centre and a complex of secondary spots, collectively called Vinalia Faculae, on its eastern floor, appear to be deposits of carbonate-rich salts — residue from briny flows that gurgled up from a fluid reservoir (perhaps a global ocean) deep in the asteroid’s interior. Occator was gouged into the landscape about 34 million years ago, but the whitish dome at its centre is much younger — just 4 million years old. That’s the conclusion of a new analysis published in the March 2017 Astronomical Journal by Andreas Nathues (Max Planck Institute for Solar System…

AFTER THE VIOLENCE of the Big Bang fully subsided, some 370,000 years later, the universe was filled with cool, neutral hydrogen gas. But those cosmic dark ages came to an end when the energetic radiation of the first stars and quasars started to ionise their surroundings. Over time, these growing bubbles of hot gas became ever more numerous. Eventually, they started to overlap each other and, in the end, intergalactic space became ionised. Astronomers can learn a lot about the early evolution of the universe by studying this Epoch of Reionisation (it’s called re-ionisation because the gas started out in an ionised state right after the Big Bang). Neutral hydrogen atoms naturally emit at a radio wavelength of 21.1 cm (a frequency of 1420.4 MHz), but the radiation from these…

“The others cast themselves down upon the fragrant grass, but Frodo stood awhile lost in wonder. It seemed to him that he had stepped through a high window that looked on a vanished world. A light was upon it for which his language had no name. All that he saw was shapely, but the shapes seemed at once clear cut, as if they had been first conceived and drawn at the uncovering of his eyes, and ancient as if they had endured for ever. He saw no colour but those he knew, gold and white and blue and green, but they were fresh and poignant, as if he had at that moment first perceived them and made for them names new and wonderful.” — J. R. R. Tolkien, Fellowship of…

It has been eight years since we last surveyed Scorpius, so let’s revisit a couple of the gems of this region, along with others not previously described. To begin, Antares is a challenging pair, only 2.5" apart and with more than 3 magnitudes brightness difference. Seeing it double is a challenge because it depends greatly on air steadiness — sometimes it’s achievable with 10 cm aperture, at other times not even with 20 cm or larger, which shows how difficult it can be to see a 5th-magnitude star when it’s close to a brighter one. Nu Scorpii , the ‘southern double double’ is less challenging, and one of my favourite combinations. Here we have two doubles in the same field — at low power a wide pair of stars, each…

Winter is the season of rugging up to observe the central regions of the Milky Way, when the temptation is to stay warm in bed. Sometimes the most fun can be had in chasing down old favourites best viewed in the cold months: that brilliant line of stars in the Lagoon Nebula (M8) or the spangled shot of the Ptolemy Cluster (M7). But at other times we’re in the mood for something else, so we begin looking beyond Sagittarius and Scorpius for some new challenges. One such challenge is Lupus, which rides high overhead during winter evenings. Out of range in the summer and shoulder seasons, the Wolf offers three good options — all dark nebulae — to add to our list of winter favourites. Dark, or absorption, nebulae…

 IN THE CONSTELLATION Delphinus the Dolphin, on the evening of July 8, 1967, British observer George Alcock discovered what became the brightest nova in 25 years, peaking at magnitude 3.5. He spotted Nova Delphini 1967 (later designated HR Del) with binoculars after 800 hours of nova-searching during the previous six and a half years. While Alcock is rightly credited with discovering this star, I saw it as a 6th-magnitude interloper two nights earlier from my backyard observatory in Burbank, California — and I wasn’t even looking for novae! I saw it as a 6th-magnitude interloper two nights earlier — and I wasn't even looking for novae! I was 16 that summer and had become a prolific variable star observer. During the 1966–67 American Association of Variable Star Observers observing year,…

NASA’S MAVEN SPACECRAFT has confirmed that the solar wind stripped the Red Planet of its dense, early atmosphere, more than likely through a process called sputtering. Mars wasn’t always the frozen, barren place it is now. Based on the ratio of various gas isotopes, scientists have long suspected that the Red Planet lost anywhere from 25% to 90% of its initial atmosphere, with the estimates favouring at least 50%. One explanation has been that the solar wind stripped it away. Now, MAVEN scientists have confirmed this hypothesis. Using the spacecraft’s measurements, Bruce Jakosky (University of Colorado, Boulder) and colleagues determined the abundances of the noble gas argon-36 and of the heavier isotope argon-38. The latter naturally settles lower in the Martian air, leaving argon-36 enriched in the upper atmosphere. This…

ALTHOUGH THE SPACE PROGRAMS of the major nations have been always largely been engineering and logistic endeavours to ‘prove it could be done’ and to gather scientific information upon the way, these enterprises have also long carried geopolitical baggage. The 1960s ‘race to the Moon’ between the United States and the Soviet Union was largely the Cold War played out in space, with the early victories to the Soviets and the ultimate prize to the Americans. Significant successes by one or the other could be trumpeted as evidence of the superior technology of that state, and by extension the superiority of its political and economic system. Although that ideological spirit has largely faded now, it persisted for many years. The US was very keen to complete its first soft landing…

“Farewell, Rosetta. You’ve done the job. That was space science at its best. Thank you.” With those simple words from mission manager Patrick Martin, the Rosetta effort was over. Mission complete. The audacious European Space Agency project that had been in flight for 12½ years ended on September 30, 2016, with a controlled thump onto the surface of the comet it had studied in exquisite detail. It was a poignant moment for those of us who’d been involved for two decades or more. But there was also a sense of relief. After countless hours spent planning and executing how to put a spacecraft in orbit around an irregularly shaped and unpredictably temperamental nucleus, we found ourselves with time to dig deeply into the treasure trove of data that Rosetta and…

The star TRAPPIST-1 is an unassuming, M8 red dwarf star. It lies 39 light-years away in the direction of Aquarius, shining at a measly apparent magnitude of 19. Closer in size to Jupiter than to the Sun, the dwarf puts out less than a thousandth as much light as our star. Last year, Michaël Gillon (University of Liège, Belgium) and colleagues announced that a trio of small exoplanets orbits this pipsqueak star. The team detected the exoplanets using the transit technique, which catches the tiny dip in starlight when a planet passes in front of its host star from our perspective. Now, after an intensive follow-up campaign, the observers have discovered that there are actually seven planets, not three. All are likely rocky. At least three lie in TRAPPIST-1’s putative…

They say it’s a small world, and it seems that in astronomy circles it has been for some time, as there has always been a two-way street between observers and researchers. The American Association of Variable Star Observers (AAVSO), for instance, is an interface between observers and the wider astronomical community. To illustrate: the star U Herculis’ variability was first documented in 1860 by Karl Ludwig Hencke, a Prussian postal clerk. His interest in astronomy had led him into contact with professionals such as Encke, von Fraunhofer and Argelander — famous names all. So, U Her it was a case of a discovery by an amateur who was motivated by professionals. The U Her data set proper began in 1863, with the work of professional astronomers in England and Germany.…

EVERY MONTH WE WATCH THE MOON morph through its sequence of phases — from new to full and back to new. During this 29½-day-long cycle, our satellite orbits around Earth, and we see its disk become sunlit from different angles. Day by day, the line that divides lunar day and night, called the terminator, gradually marches across the Moon’s face. And what an interesting face it has! Over time we’ve come to appreciate that the lunar surface preserves geologic events that occurred throughout the Solar System’s 4½-billion-year history. And guess what? You can see much of that evidence easily with even a small telescope. So here’s a list of 25 lunar features of all types that you can track down at your leisure. Use the map above to locate them;…