Indholdsfortegnelse for March 2023 i Australian Sky & Telescope

DISCOVERIES Of all the observable celestial events, the one that most terrified the ancients was a total eclipse of the Sun. Suddenly, and seemingly without warning, the light of the Sun would be extinguished, and the world would go dark. It was judged an ill omen. Today we find a total eclipse of the Sun to be a memorable experience, even if we do not expect bad things to follow. The ancient Babylonians (aka the Chaldeans) lived between 2,000 and 400 years ago, in the region now occupied by Iraq and part of Syria. Because they thought an eclipse of the Sun foretold some significant event, they paid special attention to them, and for hundreds of years their sky-watchers observed and recorded these occurrences. Initially the events seemed random, occurring…

DATA OVERLOAD ASK SOMEONE TO NAME a revolutionary space telescope right now, and they will probably answer ‘James Webb’. Ever since its launch in December 2021, this versatile successor to the Hubble Space Telescope has been stealing the astronomical limelight. But operating from the same part of the Solar System, some 1.5 million kilometres behind Earth's nightside, is a lesser-known instrument that is one of the most successful space science missions ever built: the European Space Agency's Gaia spacecraft. Gaia and Webb are very different. Whereas Webb is the instrument of choice to study selected astronomical objects in detail, Gaia is an all-sky surveyor. Its main mission: to collect precise data on positions, distances, motions and compositions for almost 2 billion stars and extragalactic objects. It is the ultimate astronomical…

CELESTIAL CARTOGRAPHY SINCE 1930, the International Astronomical Union (IAU) has officially recognised 88 constellations. The saga of how we got there is an interesting one that involves a colourful cast of characters — some familiar, some not. Many cultures have their own star lore, but the constellations we use today are largely derived from Western sources, starting with the 48 groupings that Claudius Ptolemaeus (Ptolemy) described in his 2nd-century Almagest. Ptolemy didn't draw any celestial maps that we know of — but the Almagest contained a catalogue listing the constellations and their associated stars. There were no set boundaries, so some stars were shared by neighbouring constellations. Shortly after Johannes Gutenberg invented the printing press in the 15th century, terrestrial maps, globes and atlases began to appear. These efforts were…

Get your 7x50 binoculars or similar at the ready and come on a journey to meet a superstar. Face south and follow Alpha and Beta Centauri to the Southern Cross and then on to NGC 3372, the Carina Nebula. Next, centre your binoculars on the nebula and the star Eta Car itself, which is currently 4th magnitude. Flere, we are looking out of the local Orion arm of the Milky Way, across a void, through several molecular clouds, and down into the length of the Carina-Sagittarius arm. It is 8,500 light-years to NGC 3372. Here, too, are found the massive clusters Trumpler 16 (the probable home of Eta Car), Trumpler 14, Collinder 228 and the Carina OB2 stellar association. Keeping in mind that distances can be uncertain, our variable star…

SUBURBAN STARGAZER Behold Orion, arguably the night sky's finest constellation. Gaze northward on any clear late summer night, and you can't miss the mighty celestial Hunter standing tall, near the meridian. Ruddy Betelgeuse brilliantly marks one shoulder, blue-white Rigel the opposite foot. A line of three 2nd-magnitude stars symbolises the famous belt around Orion's waist. A 1⅔°-long row of dim dots arranged nearly vertically beneath the Hunter's belt represent his sheathed sword. The southern tip of the sword is a clean, bright point. From there, trending northward, three more parts become progressively fainter and fuzzier — a clue that the Sword of Orion is more than a mere asterism. Any telescope (or even binoculars) will resolve the deceptively indistinct Sword into double stars, open clusters and nebulae — including the…

TELESCOPE TRENDS THE PLANETS ARE THE AMONG the most rewarding targets for backyard telescopes, but they can also be the most challenging. Although planetary observing is all but immune to the effects of light pollution, it is particularly sensitive to atmospheric turbulence — what astronomers refer to as ‘seeing’ — the principal enemy of telescope performance. Grappling with issues of optical design and thermal properties, aficionados strive for instruments optimised specifically for the task. In recent years, notions of what constitutes the best planetary telescope have embraced Voltaire's axiom “the perfect is the enemy of the good,” often with surprising results. Atmospheric limitations Historian and AS&T Contributing Editor William Sheehan once compared planetary observing to “watching a motion picture in which the camera is out of focus except for an occasional…

PRO-AM COLLABORATION Everybody enjoys a good meteor shower. But did you know that something as tiny as a meteoroid can cause fatal damage if it slams into a spacecraft? That might be what happened to the satellite Olympus-1 in 1993 during the Perseid meteor shower, when it spun out of control. Engineers managed to stabilise the craft, but the operation consumed so much propellant that they ultimately had to shepherd the satellite into the ‘graveyard orbit’. Imagine if that happened to a spacewalking astronaut. A millimetresize meteoroid travelling at, say, the speed of a Perseid (around 60 km/s) would puncture a hole in our the spacefarer's suit, too small to find before all the oxygen leaked out. Inevitably, the poor astronaut would suffocate. It hasn't happened. Yet. Statistics show there's…

NEWS NOTES THE DEATH THROES of stars can quite literally be the end of the world for their planets, as they are vaporised or flung onto infalling orbits. Now, scientists report in the December Monthly Notices of the Royal Astronomical Society an analysis of one of the oldest of these planetary graveyards: a red-hued white dwarf about 91 light-years away that's polluted with planetary debris. The European Space Agency's Gaia spacecraft first identified this white dwarf, WDJ2147-4035, as having unusual properties. Abbigail Elms (University of Warwick, UK) analysed this and another unusual one, WDJ1922+0233, which is bluer and a bit farther away at 128 light-years. Both stellar remnants were already known to be contaminated and cool. To take a closer look at both of the white dwarfs’ composition and temperature,…

THE GREEK ASTRONOMER Hipparchus drew up the very first star catalog of the western world sometime between 162 and 127 BCE, recording names, descriptions, and coordinates of some 850 stars. At least, that's what later sources say. No one has found copies of Hipparchus’ list — until now. Writing in the Journal for the History of Astronomy, three European scientists claim to have uncovered a small part oi the long-lost catalogue. “I felt nothing short of awe when I first heard about it,” says astronomy historian William Sheehan. “[The find] illuminates a crucial moment in the birth of science, when astronomers shifted from simply describing the patterns they saw in the sky to measuring and predicting them,” astronomy historian James Evans (University of Puget Sound) told Nature. Peter J. Williams…

STARS AND PLANETS ASTRONOMERS HAVE CONFIRMED the existence of more than 5,000 exoplanets to date. The vast majority of these — approximately 95% — orbit stars in an evolutionary stage akin to that of our Sun, a stage known as the main sequence. Main-sequence stars actively fuse hydrogen into helium in their dense, hot cores. Stars spend the vast majority of their nuclear-burning lives in this stage: In the case of a Sun-like star, the main sequence comprises 90% of the total stellar life cycle. But what about the 5% of known exoplanets found around aging stars? These stars bear exotic names like subgiants, red giants and white dwarfs, and they have evolved to have vastly different sizes, temperatures and luminosities than they did when they were young. Any planets…

BINOCULAR HIGHLIGHT I grew up in a wide-open, flat rural area, and on clear nights the bright stars and clusters of late summer and early autumn remind me of moonlight on the fields and the lights of distant towns. Many parts of the the Milky Way at this time of year are so packed with wonders that the sky seems almost cozy. Our targets this month are the open clusters NGC 1807 (magnitude 7.0) and NGC 1817 (magnitude 7.7), on the southern border of Taurus, the Bull. Or perhaps I should say our target, singular? The two groups of stars are equally distant, at about 5,900 light-years, and astrometric studies suggest that NGC 1807 may be simply a clump of 8th- to 10th-magnitude stars on the western edge of a…

Early autumn should see three comets within visual reach of backyard telescopes for southern observers. Two of them will probably be accessible to moderate-sized binoculars, given favourable sky conditions. The third will be somewhat fainter, though still within the reach of 20cm reflectors according to current predictions. The long-visible C/2017 K2 (PanSTARRS) begins autumn in the faint constellation Horologium at a predicted magnitude within the range 8.5 to 9. Moving slowly as it recedes from the Sun, it will cross into neighbouring Eridanus at the end of the third week of March, remaining within that constellation for the rest of March and April period. It is expected to have faded to around magnitude 10 by the end of April. The second relatively bright comet to grace our autumn skies will…

A quick look at the full Moon reveals two main types of lunar terrain: expansive, light-hued regions and large patches of dark material. Closer study shows the bright material to be ancient highlands dominated by impact craters, while the dark regions consist of younger basaltic lava flows (maria) at lower elevations. Maria have far fewer impact craters than do the highlands, implying that by the time maria formed (mostly after 3.8 billion years ago), the rate of crater formation had greatly subsided. By coincidence, the Moon's cratering rate declined to a very low level at about the same time as the start of lunar volcanism, which was caused by internal heating from radioactive decay of thorium, potassium and uranium. Cratering continues today at a low level, while volcanism peaked around…

Photographer Edward Weston famously once said that “Good composition is merely the strongest way of seeing.” As astrophotographers, it's easy for us to become obsessed with the technical aspects of the pursuit. But too much pixel peeping leads to the classic problem of not seeing the forest for the trees. At some point, you need to step back and consider how you go about composing your photos. Three closely related factors determine how compelling your images end up being: scale, framing and cropping. Master these and you'll be on your way to creating your best work. The Goldilocks zoom The size of your camera's sensor in conjunction with the focal length of its lens determine its field of view. Careful planning will help confirm the combination you plan to use…

ASTRO EDUCATION Over five days in October 2022, enthusiastic citizen scientists converged on Tamworth in NSW with a common aim - to immerse themselves in five days of intensive astronomical activities. Travelling from as far away as Cairns, Brisbane, Sydney and Melbourne, they were drawn by the unique opportunity of hands-on learning offered by the inaugural Tamworth Astronomy Experience. Organised by the passionate volunteers of the Tamworth Regional Astronomy Club (TRAC), with assistance from Dr Stephen Bosi, Senior Physics Lecturer at the University of New England, this event provided a unique and engrossing experience for the participants. Most of the attendees were retired professionals, keen to learn about topics such as space travel, making lenses and mirrors, and astrophotography processing. Also in attendance were two very bright 16-year-old students with…

UNTIL RECENTLY, there were dozens of ideas for what powers fast radio bursts (FRBs), ultra-bright flashes of radio waves visible from billions of light-years away. But when astronomers found multiple FRB-like bursts coming from a nearby highly magnetic neutron star, or magnetar, the question of FRB origins seemed to be largely settled. However, studies published in the journals Nature and Nature Communications on FRB 20201124A disagree on its origin. Over several months in 2020, Heng Xu (Peking University, China) and colleagues detected 1,863 bursts from the source using the Five-hundred-metre Aperture Spherical radio Telescope (FAST) in China. The FAST data included polarisation, which, to the team's surprise, revealed that the magnetic field and/or the plasma density around the source sometimes changed dramatically over only a few days. Team member Fayin…

The James Webb Space Telescope's mid-infrared observations have revealed unprecedented detail in the bizarre system known as WR 140. Two massive stars dance at its centre: an O star emitting a weaker wind and a Wolf-Rayet star blowing off a stronger, carbon-enriched wind. For a few months every eight years, when the two stars come closest together in their mutual orbit, their winds slam into each other to make carbonenriched dust, the building block of planets and possibly life itself. Previous images have shown two nested dust shells around the stars. In the new images, Webb revealed 17 nested shells of dust, representing 130 years of close approaches and dust-forming events. Ryan Lau (NSF's NOIRLab) and colleagues published the results in the journal Nature Astronomy. They also took a spectrum…

ASTRONOMY'S WORKHORKHORSE THE TELESCOPE USED MOST across professional astronomy isn't the biggest or the newest, and it isn't in space. It's a modest telescope on a mountain in New Mexico. The images and spectra from this facility, the Sloan Foundation 2.5-metre Telescope at Apache Point Observatory, are so ubiquitous that many astronomers don't even think about where the data come from. But this unassuming telescope and the (so far) five phases of its Sloan Digital Sky Survey (SDSS) have revolutionised how astronomers work. The original idea behind the SDSS was to make an enormous map of the universe. To do this, the collaboration developed a huge digital camera, which held the record for being the largest camera in the world for over a decade. Before megapixel smartphones became our pocket…

COSMIC RELIEF IN COMPARATIVE PLANETOLOGY we can't run controlled experiments, altering factors such as initial makeup or distance from a star and then seeing what happens over billions of years. We can only study the random experiments nature has chosen to run and try to piece together the overall story. The closest we may ever get to a controlled experiment for Earth's evolution is a comparison with Venus. Our sister world seems to have started with similar ingredients and conditions as our planet — though about a third closer to the Sun — yet it evolved into such a different planet. We're still trying to work out the timing and mechanisms for this divergence, and to find evidence for or against past oceans on our sibling world. These questions are…

Following 1 Ceres is going to be a lot of fun this month. It reaches opposition on March 21 in Coma Berenices at magnitude 6.9 — its brightest apparition in five years. From the very darkest skies, experienced observers might be able to glimpse the tiny world naked eye. On opposition day, Ceres lies 239.5 million kilometres from Earth. It won't be as bright or as close again until 2032. Most of us will find binoculars necessary for keeping an eye on this dwarf-planet/asteroid as it arcs through the northern half of the Virgo Galaxy Cluster, the richest and brightest such collection in the sky. The diagram shows Ceres’ path from March 1 to April 5. To find it as March begins, start at 2.8-magnitude Epsilon (ε) Virginis and slide…

The Astronomical Society of NSW's (ASNSW) South Pacific Star Party (SPSP) will be held from May 18 to 21, at the Society's rural site, ‘Wiruna’. This long-running (30 years!) astrocamp is a highlight of the calendar, giving amateurs the chance to observe under some really dark skies. You can bring your own telescope or line up to use the Society's 63.5cm (25-inch) and 44.5cm (17.5-inch) scopes. You'll also need to bring your own camping equipment or caravan/camping vehicle. Catering will be provided by the 1st Kandos Scouts, for which the SPSP is their main annual fundraiser. Apart from self-directed observing, activities will include talks and workshops, twilight sky tours, telescope sky tours, an astroimaging competition, festive roast dinner and a lucky prize draw. The keynote presentation will be given by…

FOCAL POINT For well over 40 years I have been visually timing the occultation of stars by the Moon, and to-date have bagged more than 10,000 of them. In the late 1970s I also began observing the occultation of stars by asteroids. But asteroids are small and the predictions weren't great; as a result, my early attempts had less than a 5% success rate. Fortunately, accuracy has now been greatly increased and success rates are vastly improved. These days, too, many observers use low-light video cameras that provide a permanent and very accurate record, and, if employing longer integration times, can reach magnitudes well beyond those achievable by the visual observer. Nevertheless, there is still an excitement in the ‘hands-on’ experience of visual observing, when you see a star ‘wink…