Innholdsfortegnelse for April 2015 i Australian Sky & Telescope

You know you're getting old when things that were around in your younger years are still around today. I was in my mid-20s when the Hubble Space Telescope was launched in April 1990, and I still remember the excitement that accompanied the event. I also remember the shock and disappointment when it was discovered that the telescope had a flawed primary mirror that produced fuzzy images. And the relief when the first servicing mission fixed that flaw three years later. Hubble has been around a long time now. A whole generation of young scientists are using it today who weren't even born when it was launched. In fact, two generations have come and gone since the telescope was first proposed at the beginning of the 1970s. It's almost impossible to…

Despite rescue efforts, no one has heard from one of NASA’s Stereo (Solar Terrestrial Relations Observatory) spacecraft since October. The Stereo spacecraft circle the Sun in orbits similar to Earth’s, with Stereo A ahead of Earth in its orbit and Stereo B behind. The duo thereby watch our star’s activity from angles we can’t observe. Both craft have currently drifted behind the Sun, meaning that their radio antennas must point near the Sun to communicate with Earth. To protect the equipment from overheating, mission controllers decided to point both craft away from the Sun (and Earth) and to put them in safe-mode hibernation for about a year until they drifted to safety. Stereo A successfully began its “time out” on August 20. A month later engineers were completing Stereo B’s…

Eight Billion Oort Asteroids? A fresh look at asteroids moving in comet-like orbits concludes that asteroids must make up about 4% of the Oort Cloud (see page 30). The problem began with the discovery in 1996 of 1996 PW, which had the highly elongated orbit of a comet but looked like an asteroid. Since then, dynamicists have come to suspect that the giant planets’ orbits changed dramatically in the early Solar System, flinging small bodies everywhere. Writing in the January 11th Monthly Notices of the Royal Astronomical Society, Andrew Shannon (University of Cambridge, UK) and colleagues used computer simulations to confirm that lots of rocky bodies originally within 2› astronomical units of the Sun should now be lurking among the Oort Cloud’s half trillion comets. The estimated 8 billion objects…

April 2005 Black holes shape their surroundings The huge galaxy Messier 87 (M87) in the constellation Virgo presents us with a fundamental mystery: Why is it so big, yet not much bigger? Understanding the formation of galaxies is one of the great frontiers of modern astrophysics, and giant elliptical galaxies such as M87 present a particularly stark puzzle: something appears to have abruptly halted (and is still preventing) their growth. It seems monster black holes don’t just swallow matter without a trace — they sculpt the galaxies and galaxy clusters in which they live. April 2010 Is there water on the Moon? The concept was simple: Slam a big enough bullet into a permanently shadowed lunar crater, and the resulting plume of debris should be infused with water vapour that…

The rings of Saturn are among the wonders of the Solar System. In recent decades, thanks to close-up and long-term observation by space probes such as Cassini, we have come to know their glories in intimate detail. But for centuries they were a puzzle, and we discovered their true nature only in the last hundred years or so. The key discovery has an April date. Galileo was the first to glimpse the rings more than 400 years ago but his pioneering telescope was too crude to let him see what they actually were. The drawings in his famous book The Starry Messenger, published in 1611, show a planet with a bump on either side, like the handles on a bowl. Galileo hypothesised that his indistinct observations were of a “triple…

Despite what the name implies, voids aren’t completely empty. The Bootes void, for example, contains 60 known galaxies in a region about 300 million light-years across. For comparison, the Local Group — of which the Milky Way is a member — has roughly the same number of galaxies squeezed into a space just 10 million light-years across. Roughly speaking, voids have 10 times fewer galaxies per volume than the cosmic average, and 1,000 times fewer galaxies per volume than a galaxy cluster, Vogeley says. Void galaxies are unique because they form and evolve in such a desolate environment. Galaxies in groups tend to collide, whether in glancing interactions or in full-on mergers; both serve to disrupt their gas and produce stellar baby booms. In crowded cluster environments, a hot gas…

In 1781 William Herschel discovered Uranus, the first planet not easily observable with the naked eye. Astronomers found Uranus’ orbit to be peculiar, as if a more distant planet’s gravity pulled on it. A search for this unseen planet led to the discovery of Neptune in 1846. Neptune’s motion was also thought to be peculiar, which led to the discovery of Pluto in 1930. But astronomers have now determined that Pluto is only about 2,322 kilometres in size, which is smaller than Earth’s Moon, and not massive enough to affect Neptune’s orbit. Later observations revealed that Neptune’s motion was as expected, and no massive perturber was called for. Our exploration of the outer Solar System was just beginning, however, and it continues today, with new discoveries and new mysteries arising…

The swath of Milky Way running south through Canis Major and into Puppis is rich with open star clusters — some of them well known, some not. Situated near 2.2-magnitude Zeta (›) Puppis is a trio of fine binocular targets. Let’s begin west of Zeta with the splashiest cluster of the three, NGC 2451. It’s a loose collection of more than a dozen stars scattered across about one degree of sky. Several curving rows of stars seem to emanate from a single, 3.6-magnitude star near the cluster’s centre. Through my 10Ч50 binoculars, it almost looks like a child’s connect-the-dots rendering of a face-on spiral galaxy. Just to the east, and in the same binocular field as NGC 2451, lies NGC 2477. The two clusters are a study in contrasts. Whereas…

The Sun Disc from Astrovisuals represents a revolution in Sundial design. Unlike most other Sundials (which can generally be used only in one place) the Sun Disc can be used anywhere on Earth. Its rotatable disc even allows it to be adjusted for Daylight Saving Time, making it consistently able to read the actual time! Invented, designed, and manufactured in Australia by David Widdowson, the Sun Disc uses modern materials and design to create a new twist on one of the world’s oldest measuring devices. The use of clear and white plastic creates a stylish, minimalist design that makes the Sun Disc an attractive feature for the garden, sundeck, poolside or outdoor setting. 21cm in diameter, the Sun Disc comes flat-packed in an A4 size bag and is easy to…

I’ve always loved canines, so going to the dogs sounds pretty good to me, either here on Earth or in the night sky with Canis Major and Canis Minor. Canis Minor gets short shrift when it comes to attention. The Little Dog hosts few bright stars or deep sky wonders to draw us its way. Yet there are some worthy of homage if you know where to look. One of the most interesting for small-scope enthusiasts is the possible open cluster, the ADS 6366 Group, also known as Herschel 1. On December 20, 1827, John Herschel swept up the multiple star at the heart of the group. He noted that it was “in a small cluster of 8 stars,” which he sketched. Despite its early discovery, the ADS 6366 Group…

The autumn sky is home to several of the season’s top planetary nebulae. These ephemeral celestial gas bubbles are among the most beautiful and fascinating objects in the sky. Many have a high surface brightness, making them excellent targets for small scopes and revealing a wide variety of structural features through larger instruments. Most planetaries glow brightest in the greenish light of 5007 angstroms, emitted when oxygen is doubly ionised by ultraviolet radiation from the central star. As a result, an O III line filter or a narrow bandpass filter can dramatically increase the contrast, both from light-polluted locations and dark sites. When the seeing permits, remove the filter and pump up the magnification to search for small structural details. William Herschel picked up NGC 2392 in a January 1787…

I highlighted Jerry Oltion’s 12.5-inch binocular telescope in the February/March issue. That scope has many interesting and novel features, but one I feel merits particular attention is its superb focuser. As Jerry notes, “when you make two of everything, you favour designs that are cheap and simple!” All told, the parts for his focuser add up to less than $10. That’s the “cheap” part of the equation, but what about “simple”? Jerry’s focuser is essentially a Crayford design, which means it doesn’t utilise the usual rack-and-pinion mechanism found in many commercial units. In a Crayford focuser, a rotating shaft presses against the focusing barrel, which moves back and forth against a set of bearings. In Jerry’s version, the mechanism is contained in a 92-mm-square, 45-mm-deep box made from 12.5-mm plywood.…

Dawn arrives at Ceres NASA’s intrepid Dawn spacecraft enters into orbit around the largest body in the main asteroid belt, the dwarf planet Ceres. A virtual observatory What famous observatory has no lens and no mirror? It's the WorldWide Telescope, an interactive web browser for the sky. And best of all, it’s free. Astronomy apps Astronomy apps crowd the Apple and Android app stores. We asked our experts to recommend some of the best. NASA's flying observatory After two decades of trials and tinkering, the Stratospheric Observatory for Infrared Astronomy is finally flying high. FIND US ON FACEBOOK…

The astronomical community is mourning the passing of Graham Blow on December 31, 2014. He was 60 years old. Graham had an interest in astronomy from an early age, receiving a 2.5-inch refractor on his 15th birthday. In 1970, he joined the Auckland Astronomical Society, and later the Variable Star Section, and made observations of variable stars using his refractor. He soon became involved in observing total and grazing lunar occultations. In 1973 Graham assisted in forming the Auckland-based National Junior Coordinating Committee (NJCC) for young astronomers. The NJCC became the National Committee for Student Astronomy in 1974 with Graham as chairman. In 1978 he joined the staff of the Carter Observatory and was scientific officer until it was restructured 17 years later, during this time completing a master's thesis…

Snake Valley Astro Camp March 20-22 Snake Valley, Vic Phone: 03 5231 3048 WA Astrofest March 28 Biennial Victorian astronomy conference, hosted in 2015 by the Bendigo Astronomical Society astronomywa.net.au VASTROC April 17-19 Biennial Victorian astronomy conference, hosted in 2015 by the Bendigo Astronomical Society vastroc.net RASNZ Conference May 8-10 Annual meeting of New Zealand's astronomers rasnz.org.nz/Conference/ Trans-Tasman Symposium on Occultations May 11 Australasian get-together for occultation observers, this year to be held in Lake Tekapo, NZ occultations.org.nz South Pacific Star Party May 14-17 Annual star party hosted by the Astronomical Society of NSW asnsw.com/spsp CWAS Astrofest July 18-19 Annual conference held in Parkes (home of 'the Dish'), including the David Malin Awards cwas.org.au/Astrofest/ Queensland Astrofest August 7-16 Annual star party qldastrofest.org.au National Science Week August 15-23 Lots of public…

It seems hard to believe, but the world's most famous telescope was launched into orbit 25 years ago this April. During that quarter of a century it has revolutionised our understanding of the universe… and produced some of the most stunning images ever taken. On these pages we present a handful of its most famous portraits… it's our photographic tribute to the Hubble Space Telescope and the engineers and scientists who made it all happen.…

Even inside a void, an extraterrestrial’s night sky wouldn’t look that different from our own — most of the celestial objects we see, after all, are stars within our own galaxy. In fact, a void galaxy would have a higher star formation rate for its size than the Milky Way, so star-forming features such as the Orion Nebula might be more prevalent. But peering through a telescope would probably not show any other luminous galaxies for many millions of light-years. Vogeley estimates that galaxies in a typical void are an average million fifty light-years apart, twice the average distance between galaxies in the Local Group, and ten times the distance between galaxies in a typical cluster. So there would be no nearby Andromeda Galaxy, and no nearby Virgo Cluster. Any…

WHEN Early March 10pm Late March 9pm Early April 8pm Late April 7pm These are standard times — add Daylight Savings if it applies to your location. HOW Go outside within an hour or so of a time listed above. Hold the map above your head with the bottom of the page facing south. The chart now matches the stars in your sky, with the circular perimeter representing the horizon and the centre of the chart being the point directly over your head (known as the zenith). FOR EXAMPLE: Look at the chart, and you’ll see that the bright star Achernar at the end of the constellation Eridanus (The River) is about one-third of the way from the southwestern horizon and the middle of the chart. So if you look…

Our region this month is in the old constellation Argo, the ship of Jason and the Argonauts who went in search of the Golden Fleece. Argo was broken up into smaller parts in the 19th century, and here we'll study an area in southern Pyxis (the mariner's compass, previously Malus, the mast) and northern Vela (the sails), along the ragged edge of the Milky Way. Starting in northernmost Vela, our first destination is the bright DUN 70, located about 40 NE from 2nd-magnitude Gamma Velorum, itself a showpiece object. DUN 70 has stars of 5th and 7th magnitudes, and with a separation similar to Alpha Crucis it shows well in an 80mm refractor. Hartung described the colours as "pale and deep yellow"; I saw it as white and off-white, closer…

When I bought my first telescope that automatically pointed at objects with the push of a button a decade ago, I was embarrassed to admit it to my fellow amateur astronomers. In my mind, that wasn’t the way real astronomers worked; we squinted through finder scopes and star-hopped to targets with the aid of star charts. It didn’t take long for me to get over my embarrassment. After 35 years of hunting, I realised I was more interested in looking at objects than looking for them. Today, the majority of amateur astronomers agree, and most telescopes are sold with Go To-equipped mounts. You can see plenty of celestial objects with a Go To telescope once it’s aligned. The problem is getting it aligned properly. Before your scope can work its…

As observers, we all know that a dark-sky site vastly improves the view of deep-sky objects. But how many of us really know what this is like when taken to its ultimate? Likely only a few percent of us have enjoyed observing from a seriously dark location: black sky, not a spark of artificial light, trees visible only as silhouettes against airglow. Until you first experience it, you can’t properly envision it; too much emerges, with increasing rapidity, as you progress into deep darkness. I learn this firsthand on a trip to a national park. I want to turn my 25x100 astronomical binoculars onto the Milky Way from a place with serious darkness. It’s low season, and the six of us are alone in the park. There are no artificial…

A bizarre set of galaxies in the Coma Cluster have lost most of their stellar material, making them especially rich in dark matter. Pieter van Dokkum (Yale) and colleagues found the galaxies when they took a unique look at Coma through the Dragonfly Telephoto Array, a group of (then) 8 Canon telephoto lenses coupled to CCD cameras on a single mount. The 47 galaxies lurk on the cluster’s outskirts and are similar in size to the Milky Way — but with 1/1,000 the number of stars. To survive in Coma’s gravitational turmoil, these dark galaxies must contain 98% dark matter to hold themselves together, much higher than the fraction of matter in the universe at large (83%). Either these weirdly faint galaxies have lost their stars, or they never had…

On January 27, in torrential rain, Sydney Observatory's East Dome was launched by Museum of Applied Arts and Sciences (MAAS) Director Rose Hiscock, President of the Board of Trustees Professor John Shine, and Minister for Disability Services, the Hon John Ajaka MLC. Despite the rain, 80 guests and media attended the opening, including: eminent astronomer and ground breaking astrophotographer, David Malin; University of Sydney astronomers Professors Anne Green and Elaine Sadler; Astronomer-in-charge of the Australian Astronomical Observatory, Fred Watson; ESA engineer Warrick Holmes; UNSW Professor Michael Burton and University of Western Sydney Assoc. Professor Miroslav Filipovic. Star measurer and computer, Winsome Bellamy, and former Sydney Observatory director Harley Wood’s daughter, Ros Madden, were present. Many amateur astronomers and astronomy enthusiasts joined us and all attendees were offered a tour of…

With only months left to go before encounter day on July 14, the New Horizons mission has begun its ‘optical navigation’ phase. This is where the craft's own cameras are used to help refine its trajectory by measuring Pluto's position in relation to background stars. New Horizons is now well into the first of three approach phases (to be matched after encounter day with three departure phases). This phase has included long-range photography of the Pluto-Charon system using the craft’s Long-Range Reconnaissance Imager, or LORRI. As New Horizons starts on the final 130 million kilometre run in to Pluto, LORRI will take hundreds of images of the dwarf planet, seeing it grow slowly larger in the field of view each day. The aim is to work out whether course correction…

Space is pretty empty. And Paul Sutter likes empty. He likes it so much, in fact, that he spends his time exploring the most barren regions of the universe, vast gaps known as cosmic voids. Almost all the matter in the universe — galaxies and the mysterious, invisible stuff known as dark matter — stretches across space like a giant cobweb. Astronomers call this structure of narrow filaments and thin walls the cosmic web. The vacant expanses in between, akin to the holes inside a sponge, are the voids. The web varies in density from compact, bustling metropolises, where thousands of galaxies cluster at the intersection of filaments, to calmer suburbs such as our Local Group. But as on Earth, most of the universe is sparsely populated — voids make…

Though the names are similar, dark matter and dark energy are opposite in concept: dark matter attracts and dark energy repels. Dark matter holds roughly 27% of the universe’s energy. It doesn’t emit or absorb light, making it all but impossible to detect except by its gravitational effects. Dark energy, on the other hand, is thought to be a negative force that pervades the entire cosmos and accelerates cosmic expansion. It’s the dominant form of energy in the universe, making up 68% of the total energy budget. That leaves less than 5% of the universe’s total energy in normal matter.…

Some moons orbit near their planets, so planetary glare is of great concern when trying to locate them. Phobos and Deimos are classic examples of this, but I had glare issues the first time I tracked down Himalia, even though it was distant from Jupiter at the time. Occulting bar or filter eyepieces may be of assistance with these problems. While an occulting bar will entirely block out a planet, an occulting filter will provide a dim image of it. If you have an accurate predictive chart, this may help you locate a dim moon; you’ll know where to look in relation to its planet. The bar or filter must be mounted at the eyepiece’s focal plane, or a crisp edge won’t be generated in the image. I’ve made two…

Before dawn on August 18, 2014, I stood near my favorite local pond looking at Venus and Jupiter and their reflections. That morning, I beheld the two planets forming a brilliant pair only about 1/3° apart — not too much farther apart or much differently situated in the sky than they were when the Magi of Christian tradition might have seen them in August of 3 BC. Three days earlier, on August 15th, I had seen something just as interesting: the brightest of all stars at its famed ‘heliacal rising’ Of course, I’m talking about Sirius, which at this time of year is still and at a convenient for altitude for viewing in the evening hours. Orion the Hunter, the brightest of all constellations, leads his two hounds across the…

Spaceflight DVD Immerse yourself in stunning images of spaceflight. See the majestic curved Earth glide quietly by under you and bear witness to that one small step that forever changed humanhistory. Spaceflight DVD is two hours of visual wonder. $11.95 Eyes On The Sky DVD This 60-minute produced by the European Southern Observatory (ESO) covers the history of the telescope, its importance, and some of the technological breakthroughs. $11.95 The Universe DVD This 128-minute DVD features discoveries from the Hubble Space Telescope about star clusters, nebulae, extrasolar planets, galaxies, dark matter, the Big Bang and cosmology, and more. There is also a special section featuring the best of Hubble. A must have. $11.95 Order today by ringing (02) 9439 1955 with your credit card details handy, or you can fill…

The next total eclipse of the Moon will greet evening stargazers on Saturday, April 4. It will be the third in the current tetrad of total lunar eclipses coming at half-year intervals. This eclipse will be just barely total and last for only about 10 minutes. You may even get the impression that it never becomes quite total at all. The Moon’s north-northeastern limb will be so slightly inside the umbra (the central portion of Earth’s shadow) that it will remain much brighter than the deep red we can expect across the rest of the Moon’s face. If you’re in New Zealand, the event happens deep in the night and high in the sky. For Australia, it occurs in the evening – those in the eastern half of the continent…