Innholdsfortegnelse for April 2018 i Australian Sky & Telescope

The rings that surround Saturn are among the great wonders of the Solar System, even more so nowadays when spacecraft and powerful telescopes have revealed their astonishingly intricate beauty. Galileo was the first to glimpse them with his primitive telescope in 1610, but he couldn’t understand what he saw. The planet appeared to be not a simple disk like Mars or Jupiter, but displayed some sort of protuberances on either side. Did Saturn have ‘ears,’ or was the planet really three planets in close proximity, with the big one in the middle? He was even more puzzled two years later when the phenomenon disappeared (as a result of the Earth passing through the plane of the ‘rings’ and seeing them edge-on). In time it returned. By the end of the…

DURING THE COURSE OF A YEAR, the path of the Sun among the stars — the ecliptic — passes through 12 ancient constellations. Because all but one of these 12 constellations represent living things, human or animal, the Greeks called them the ‘Circle of Animals’ — in ancient Greek, kyklos zodiakos, now shortened to zodiac. The one star pattern in the zodiac that doesn’t represent an animal is Libra, the Scales. However, the Greeks considered the stars of Libra to be both a Scales and the Claws of the Scorpion, which follows Libra in the zodiac, so it’s appropriate to include it in the circle as well. The Greeks inherited the 12 constellations of the zodiac, as well as the concept of the zodiac as a singular object, from the…

Centaurus contains hundreds of doubles accessible to moderate telescopes. As always, I’ll try to offer some easy and attractive pairs as well as some more testing objects, a few of them requiring medium-sized telescopes (20 to 30 cm in aperture). First up is R 165, a 7th-magnitude pair nearly 3" apart, not difficult for 80 mm aperture. The yellow stars show nicely close at 100× in a field that has some middling-bright stars. It hasn’t changed much since H.C. Russell discovered it from Sydney Observatory in 1880. It’s about 5 degrees east-northeast from the nearest guide star, 2.7-magnitude Mu Velorum. From R165, 1.25 degrees north-northeast is HJ 4423, another 7th-magnitude pair with similar separation and angle, slightly unequal, and paler yellow, and again accessible to 80-mm scopes. More difficult, some…

As summer gives way to the shorter daylight hours of autumn, Venus returns to the evening sky for a long engagement — the Evening Star will remain in view through until mid-October. Telescopically, Venus never offers much to see aside from its gradual change in apparent size and an attractive progression of phases. Observers have strained for centuries to glimpse any detail on its cloud-cloaked disk. We sometimes forget that astronomers knew very little about this neighbour world — so like Earth in size and mass — until powerful radar probing and spacecraft visits started to peel back the layers of mystery in the 1960s. The first artificial satellites were still a decade away when, in 1946, Immanuel Velikovsky finished the manuscript for Worlds in Collision, a book that capitalised…

ROUGHLY A DECADE AGO, ON Semiconductor (formerly Kodak) introduced the KAF-8300 CCD detector widely used in astronomical cameras. This 8.3-megapixel, 18 x 14 mm sensor offered a generous field of view for imagers on a modest budget, and cameras built around the KAF-8300 detector quickly became the tool of choice for many deep sky astrophotographers. Today, another ON Semiconductor CCD chip is set to make a splash in the imaging market with a detector that’s nearly twice the size of the 8300 CCD: The KAF-16200, a 16-megapixel chip roughly ¾ the size of a 35-mm camera frame. With our interest piqued, we borrowed one of the first cameras to feature this chip to see how it performs in the field. Fit and finish The Chinese-made QHY16200A camera with its 27…

Amateur astronomers who value dark skies and the company of like-minded individuals will gather in May at the Astronomical Society of NSW’s South Pacific Star Party. Held at the Society’s rural property at Wiruna – about three hours’ drive northwest from Sydney – the event traditionally sees lots of big scopes and all the latest tech turn out. Full details at asnsw.com. Many of those same amateurs will have made the trek south to Ballarat at the end of March for the biennial National Australian Convention of Amateur Astronomers (NACAA). This year’s packed program will include a symposium on diversity in astronomy, a DarkSky symposium, and the Twelfth Trans-Tasman Symposium on Occultations. A diverse collection of other presentations will cover topics such as astro-tourism, education and student research. The event…

NEW DATA ON KIC 8462852, also known as Tabby’s Star, show that dust — not an alien megastructure — is causing its mysterious behaviour. Results will appear in the Astrophysical Journal Letters. Tabetha Boyajian (Louisiana State University) and colleagues reported the star’s discovery in 2016 in archived Kepler data. The star dipped in brightness by up to 22% for several days at a time. Long-term observations also showed the star fading over the years. To obtain round-the-clock observations that could catch the star as it was dipping, Boyajian launched a Kickstarter campaign to secure funding for observations with the Las Cumbres Observatory (LCO), a network of 0.4-m robotic telescopes around the globe. In May 2017 the team caught the first real-time change, a minor event that obscured 1% of the…

Looking up at a dark night sky we can see thousands of stars. Every star is a sun, and if our Sun has planets, then it makes sense that the other stars would have planets, too. And they do. Astronomers now know of thousands of these ‘exoplanets,’ and they suspect that nearly every star has a planetary system, meaning our Milky Way Galaxy is teeming with alien worlds. Thanks largely to the pioneering Kepler space telescope, we also now know that small, rocky exoplanets are common and that planetary systems are astonishing in their diversity. But many of our exoplanet searches have targeted specific areas of sky. The natural next step is to do a space-based all-sky survey. A specific plan for just such a survey mission was envisioned a…

Is there anything better than grabbing your binoculars and scanning through the star clouds of Carina? Doing so takes me back to my youth, when all I had to guide me was the famous National Geographic map of the whole sky and my mother’s 8×30 binoculars. I remember being dazzled by the seemingly endless variety of star groupings, with sparkling gems galore in every field of view. One of the prettiest of those groups is IC 2602, also known as the Southern Pleiades, located about four degrees south of Eta (η) Carinae. Described by Abbe Lacaille in the 18th century from South Africa, it’s one of the closest open clusters, around 480 light-years from Earth. Its 70-or-so stars have an average age of about 40 to 50 million years. We’ve…

The bright southern variable V Pyxidis has been brought to my attention as a potentially important and under-observed target. V Pyx was first discovered as variable in 1921 by Mary Applegate, Fellow in Astronomy at the Harvard Observatory. However, with only occasional study over subsequent years, not a lot was learned. What we know today is largely thanks to regular observation by members of the Royal Astronomical Society of New Zealand’s Variable Star Section, beginning in 1971. V Pyx is now known to have a pulsation period of 79.9 days and a visual amplitude of 7.7 to 10.4. As it pulsates, its spectral type changes from a G8 to M1 supergiant. This firmly classifies it as an ‘SRD’ semi-regular variable. So why is it an important target? As I write…

Cancer, the Crab, and Hydra, the Water Monster, are mythologically tied. They battled the great hero Hercules during the second task of his 12 legendary labours, but the tremendous crab and multi-headed beast were slain by the mighty demigod. Their constellations are joined in the sky as well, with Hydra’s head resting close beneath Cancer’s legs. Now well placed for observing in the evening sky, these foes of Hercules will be the site of our deep sky explorations. I very much enjoy the observations other amateur astronomers send me, and I’d like to showcase some that have come my way. Let’s begin in Cancer, which is shown as a Y on the all-sky chart at the centre of this magazine. The star at the Y’s fork is called Asellus Australis,…

I’ve been an active amateur astronomer and astrophotographer in one form or another for over 35 years now. In my early days, as a teenager without a driver’s licence, it was my dear old dad, Domenico Sidonio, who used to drive me to the monthly meetings of the Astronomical Society of the Hunter in Newcastle. My father, a former Italian prisoner of war of the Germans in World War II, never let me miss a meeting. He would work hard all day as a boilermaker at the BHP steelworks, then, without fail, on that Thursday of every month, he would faithfully drive me to my meetings… sometimes sleeping in the car as he waited, sometimes coming in to sit and listen to the guest speaker. At one stage in those…

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NEW ANALYSIS FROM the New Horizons team suggests that the spacecraft’s next target, a Kuiper Belt object known as 2014 MU69 , might have a moon. The object was already thought to be a binary, so this brings the party members to three. Planetary scientists presented the preliminary results at the meeting of the American Geophysical Union in New Orleans. New Horizons will fly 3,500 km from 2014 MU69 on January 1, 2019. Initial views, to be obtained in September 2018, won’t resolve the object — it won’t be until after the flyby that we’ll begin to see high-resolution images of its surface. Data will continue trickling in through 2019 and most of 2020. Meanwhile, New Horizons will also be exploring 30 other Kuiper Belt objects from much greater distances…

A UNIQUE COLLABORATION between an astronomer and a Google engineer has led to the creation of a kind of artificial intelligence known as a neural network. Set to work on data from the Kepler mission, the algorithm discovered two new Earth-size planets, one of which is part of the first eight-planet system outside our own. Neural networks are loosely based on connections between neurons in the brain. Each ‘neuron’ is a simple mathematical formula that acts like a switch, turning on when it recognises a certain pattern. Each set of neurons passes its results on to the next layer. By combining layers, Christopher Shallue (Google Brain) built an algorithm that can identify exoplanet transit signatures in stellar light curves. It learned how by training on a set of 15,000 Kepler…

As geologists and mariners have long known, Earth’s magnetic field is dynamic and ever-changing. The location of our planet’s north and south magnetic poles are both wandering, recently by as much as 40 kilometres per year. The strength of Earth’s field varies significantly from one location to another — in the South Atlantic Ocean, for example, the field is only half as strong as the global norm. Even the familiar north-south polarity is not fixed for all eternity. The paleomagnetic record clearly shows that our planet’s field is capable of flip-flopping in such radical fashion that north becomes south and south becomes north. In fact, Earth’s magnetic field has weakened overall by about 9% over the past 175 years. This has led to concern that our home planet could be…

Our universe emits radiation over an incredible range of wavelengths, from the infrared glow of dust that shields the youngest stars to gamma rays from distant supernovae. Earth’s atmosphere blocks all but a tiny fraction of these colours, though, and the light that does make it to Earth’s surface blurs as it passes through the air. To compensate, astronomers build high-tech telescopes on tall mountains. Yet even the highest astronomical observatory in the world, the University of Tokyo Atacama Observatory (5,640 metres), sits above only about half of Earth’s atmosphere. An even better solution is to place telescopes in space, but such projects are expensive: NASA’s exoplanet-hunting Kepler mission cost US$600 million, and that’s on the low end. The high cost of space-based telescopes means that scientists can construct few…

The Eta Aquarid shower never fails to put on a good show, and is best seen from our southern skies. Like the Orionids in October, the Eta Aquariid meteoroid stream is associated with comet 1P/Halley. The meteors are often fast and bright and are usually yellow, although orange and blue is also often seen. Many of them leave persistent trains, some lasting for minutes. In recent years, overall rates as well as the number of bright meteors have been increasing. The average magnitude has increased to 2.4, and fireball and bolide activity, although low, is also on the rise. International Meteor Organisation (IMO) analyses based on data collected between 1984 and 2001, have shown that the zenithal hourly rates (ZHRs) are generally above 35 in the period May 3 to…

The samples returned by six crews of Apollo astronauts from 1969 to 1972 showed us, finally, what the Moon was made of. Completely unlike the sopping-wet Earth, those lunar rocks revealed no evidence of water or even any minerals remotely related to water. I vividly recall the first science results from Apollo 11 and hearing the phrase, “The Moon is bone dry”. But during the last decade teams of researchers have used improved laboratory instrumentation to reveal water chemically bound within some lunar samples, suggesting that it came from the Moon’s interior. The Apollo samples tell us about only half a dozen locations on the lunar surface. However, thanks to the Moon Mineralogy Mapper (M3 ), a visible-infrared spectrometer on the Indian lunar orbiter Chandrayaan 1, we’ve known for nearly…

THE VERSATILE AND PORTABLE SCHMIDT-CASSEGRAIN telescope is without question among the most popular type of commercial telescopes ever sold. However, some amateur astronomers don’t respect the SCT, regarding it as an also-ran optically compared to other designs. The fact is, SCTs are better telescopes than observers often acknowledge. At least they can be, if properly collimated by ensuring that the telescope’s large primary and smaller secondary mirrors are properly aligned. Unfortunately, many of the SCTs I encounter are out of collimation, and yet the owners are sometimes afraid to adjust their telescopes’ optics. The idea of collimating a complicated-looking telescope is admittedly scary, but there’s really nothing to fear. The SCT is actually easier to collimate than any other design. Only one optical element needs to be, or can be,…