Indholdsfortegnelse for April 2020 i Australian Sky & Telescope

THE PARKER SOLAR PROBE TEAM has announced key findings from the spacecraft’s first two perihelion passes in November 2018 and April 2019. These results mark the first public release of data from NASA’s flagship heliophysics mission, which aims to understand the Sun’s outer atmosphere, or corona, and the solar wind that emanates from it. During its first two passes Parker already swooped within 24 million kilometres of the Sun’s visible surface, equivalent to just over half of Mercury’s distance from the Sun at perihelion, or 35 times the Sun’s radius. Parker carries a host of instruments into this hostile territory: The SWEAP instrument suite measures properties of the plasma, the FIELDS package measures magnetic and electric fields, and ISʘIS characterises high-energy particles. The Wide-Field Imager for Solar Probe (WISPR) also…

THIS MONTH THE HUBBLE Space Telescope (HST) celebrates three decades of continuous operations in Earth orbit. Conceived at the beginning of the 1970s, launched in April 1990, still going strong in 2020 and with a long list of discoveries and incredible images behind it, the HST has rightly earned its status as the world’s most famous telescope. And what more appropriate way could there be in which to celebrate the HST’s 30th birthday than with a spread of its best images? Out of the thousands that have been produced over the past three decades, the ones on these pages are just a handful that caught our eye. You can browse through hundreds more at spacetelescope.org.…

Your orientation in space is determined by your latitude and the local time, so those values are relatively easy to measure astronomically. For instance, it’s local noon by definition when the Sun is at its highest. And the Sun’s zenith distance at that moment is equal to your latitude minus the Sun’s declination, which can be found for any given day in an astronomical almanac. Longitude is harder because all people at any given latitude go through the same cycle of space orientations, regardless of their longitude. Two hours from now, a person 30° directly west of you will see the Sun at the same spot in the sky that you do right now. But if you have a clock (either mechanical or astronomical) that tells you the time in…

One of my favourite objects in the autumn night sky is Collinder 121 in the constellation Canis Major, the Big Dog. It’s a complex view, because what we see isn’t all one object. Let’s start with the visual anchor of the field, the bright star Omicron1 (01) Canis Majoris. It’s a monster, a K2 red supergiant, between 8 and 13 times the mass of our own Sun, and at least 220 times as large in diameter. It’s a young star in absolute terms, only 18 million years old — stars that big simply don’t last long before blowing themselves apart as supernovae. Omicron1 is only one of a gaggle of bright young stars in the field. Most of the rest are of type O and B, and they make up the…

We last visited the red supergiant Betelgeuse in our December 2011 issue. If you have been following the star since then, you’ll have seen that it has faded (see News Notes in this issue). In fact, if you had been following it you might have been the one who discovered the fading event. So if you’ve not currently monitoring Betelgeuse, why not do so now? — you might be among the first to notice something new. For instance, the red supergiant phase of the star’s life is expected to end in a supernova explosion; if and when that happens, Betelgeuse will become so bright it will be visible in daylight. Also known as alpha Orionis, Betelgeuse is a semiregular variable with a visual magnitude range of 0.0 to 1.3 (currently…

The brightest planet and the best-known naked-eye star cluster join forces on the evening of April 3 for a spectacular conjunction visible just about everywhere. That evening, for observers in Australasia, Venus will tiptoe through the outskirts of the Pleiades and nudge within about 15’ of Merope. For those in North America, Venus will pass only ¼° south of the cluster’s brightest star, 3rd-magnitude Alcyone. If this very close conjunction feels familiar, it should. A nearly identical one took place on April 3, 2012, and the next will happen on April 3, 2028. Conjunctions of the cluster and planet aren’t unusual — in fact they happen annually — with Venus passing near but rarely through the Pleiades. However, every eight years nearly to the day, Venus knocks down the door…

While Johannes Kepler was working on the first version of Somnium, his great contemporary Galileo Galilei heard of a new device that made distant objects appear bigger. Galileo built his own telescope (as we now call it), turned it to the night sky, and in one year he discovered that the Milky Way comprises innumerable faint stars, confirmed Petrarch’s theory of complex lunar topography as shown in the sketches on the facing page, discovered Jupiter’s four bright moons and observed their changing patterns. That was a severe blow to the geocentric theory, because it proved that at least four objects orbit something other than Earth! He published these results in 1610 in a short pamphlet entitled Sidereus nuncius (Starry Message or Messenger) that electrified the scientific community. Kepler was thrilled…

WHEN I WAS MUCH YOUNGER than I’d care to relate, I spent lots of time eyeing ads for 15-cm Unitron refractors. Surely, I thought, that large (and long) refractor would be the perfect telescope. And on a cloudy night I could kick back and just gaze at the scope itself. While I’ve had glimpses through large APO refractors at star parties, the lure of these classical instruments always was just beyond my grasp. When I was presented the opportunity to review the Sky-Watcher Esprit 150mm ED triplet refractor, I finally had the chance to realise my expectations. The Esprit 150ED on loan from Sky-Watcher USA arrived in a single, large box, and when removed from its rugged, fitted carrying case the scope is compelling just to look at. Though 2…

MY CITY HAS A SECLUDED park that attracts many visitors to admire its colourful flowers and to picnic on its well-tended lawns. It’s also a magnet for artists and photographers. Sometimes, mainly when sunspots are present, I’ll set up my 75-mm refractor in the middle of the park and invite passersby to safely view the white screen on which the telescope projects an image of the Sun — the ultimate nourisher of all those gorgeous flowers. I bought the 75-mm in 1978 for nighttime observing. When it arrived with a bracket and screen accessory for solar projection, I felt I’d been conned into paying for something I’d never use. In 1981 I purchased a Meade 20-cm Schmidt-Cassegrain for nighttime use and, later, a Tuthill Solar Skreen filter for observing the…

SCIENTISTS WORKING with NASA’s Transiting Exoplanet Survey Satellite (TESS) announced the official catalogue that summarises the mission’s first year of exoplanet-hunting results. From July 2018 to July 2019, TESS searched for planets in the southern sky, revealing more than 1,100 planet candidates. Of these, 37 — so far — have been confirmed via follow-up observations and the results published in peer-reviewed journals. The catalogue will be available in an upcoming issue of Astrophysical Journal Supplements, according to catalogue manager Natalia Guerrero (MIT). Like its predecessor, NASA’s Kepler mission, TESS finds planets by watching for dips in starlight caused when a planet transits across the face of its star. But unlike Kepler, TESS watches stars close to Earth. By design, all of the planets it finds are within about 3,000 light-years,…

TWO OF THE CSIRO’S radio telescope facilities — Parkes and the Australia Telescope Compact Array (ATCA) — are to receive major upgrades that will dramatically boost their productivity. Both are part of the Australia Telescope National Facility, owned and operated by the CSIRO and funded by the federal government. The upgrades are being financed by Australian Research Council Linkage Infrastructure, Equipment and Facilities (LIEF) grants. Parkes will be given a sensitive new receiver system, called ‘cryoPAF,’ which will triple the telescope’s field of view. The $3 million project is being supported by a $1.15 million LIEF grant The ‘PAF’ part of the cryoPAF name denotes that it will be a phased-array feed, which is essentially a cluster of radio antennas located side-by-side, and situated at the focus point of the…

OF THE 48 CONSTELLATIONS DESCRIBED in Claudius Ptolemy’s Almagest, 47 survive to the current day. The sole exception is Argo Navis, the ship that carried the mythical Greek hero Jason and his fellow Argonauts to the end of the known world in quest of the Golden Fleece. Its stars ended up distributed among four nautically themed constellations: Carina, the keel or hull; Vela, thes Sails; Puppis, the poop deck; and Pyxis, the compass. Pyxis is small and dim, but Carina, Vela and Puppis are all big, bright, and spangled with naked-eye star clusters. If you put them back together, they’d be the biggest constellation in the sky — much bigger than Ptolemy’s original Argo, in fact. For shorthand, I will call the original constellation Old Argo Navis, and use Greater…

ASTRONOMERS HAD HOPED TO SEE something interesting when they steered the New Horizons spacecraft on course to visit a Kuiper Belt object soon after it flew past Pluto. They chose the object 2014 MU69 because its nearly circular orbit beyond Neptune marked it as among the most primordial objects known in the Solar System, and its path put it within reach for New Horizons. They nicknamed it Ultima Thule, meaning ‘beyond the known world.’ On November 8, 2019, its official name became Arrokoth, meaning ‘sky’ in the Powhatan Algonquian language. All Hubble recorded was a tiny spot in the sky, but when astronomers watched Arrokoth occult a distant star, the little world’s silhouette hinted at a pair of objects orbiting close to, or even touching, each other. So controllers were…

PICTURE AN IMAGE OF THE CONSTELLATION ORION rising above a distant hill, with M42 and the Horsehead Nebula displaying vivid colours and wisps of faint gas and dust. The reddish crescent of Barnard’s Loop cradles the central stars of the Hunter’s belt, spanning from Bellatrix to Saiph and back to Rigel. The large glow of Sharpless 2-164, the Angelfish Nebula, surprises you with its visibility in the photograph. Surely this must be a composite — such deep images are only possible using complex processing techniques to blend the moving sky with a stationary foreground, right? Not so! While in the past such an image would have required hours of Photoshop wizardry, today’s digital sensors and fast, high-quality camera lenses make deep sky nightscapes such as this possible in a single…

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…

WE LIVE IN A WORLD made of our ancestor’s dreams, where extraordinary feats have become commonplace. Most people alive today have never witnessed a time when we did not capture exquisite images of planets, stars and galaxies; when we did not regularly shuttle members of our species to a residence orbiting 400 kilometres above Earth; when we did not plunge spacecraft into the depths of the cosmos, scattering them throughout the Solar System and beyond. In the ages before these feats, launching anything into space was mere fantasy, a collaboration of the mind and the pen. Firmly earthbound, we looked up, told stories about far-off worlds, and imagined what it might be like to visit them. The pathbreaking 17th-century astronomer Johannes Kepler authored such a story — a travelogue, an…

Stephen Russell has been engaged in Australia’s amateur astronomy scene seemingly forever. An avid eclipse chaser, he’s also been heavily involved in organising the biennial NACAA conferences and is chair of the next one, to be held in Parkes in April this year. What got you into astronomy? I was a kid during the Apollo lunar missions, and because of them became very excited by space exploration. At the age of 10, my neighbour took me along to the local astronomy club (the Illawarra Astronomical Society, IAS), in which I became actively involved for many years, even after I moved to Sydney. The IAS hosted the 1970 National Australian Convention of Amateur Astronomers (NACAA), which started another long story for me. I’ve been to all but two of the events…

In 1603, Johannes Bayer published Uranometria, the first atlas to cover the entire celestial sphere. For most of the sky, Bayer used the recent star catalogue of the Danish astronomer Tycho Brahe, which was extremely accurate. For the Ptolemaic stars too southerly to see from Denmark, Bayer used Ptolemy’s low-quality data. And for far-southerly stars he used the Dutch star catalogues, which were better than Ptolemy’s but nowhere near as good as Tycho’s. Bayer labeled the brightest stars in each constellation with lowercase Greek letters, most of which have survived to the current day. Bayer always tries to be faithful to Ptolemy’s descriptions; for instance, he shows Canopus on the end of one of the two steering oars, the ancient equivalent of rudders. He cleverly explains the fact that Argo…

TWO HUNDRED AND FIFTY YEARS AGO, in March 1770, Lieutenant James Cook of the British Royal Navy was busy mapping the coastline of New Zealand during the first of his three great voyages. Thanks to these voyages, which crisscrossed the Pacific Ocean east to west and north to south, Captain Cook (as he later became) is widely recognised as one of the greatest explorers of all time. Fewer people know that astronomy also played a major role in his life and expeditions. Cook observed transits of Venus and Mercury across the face of the Sun, a number of solar and lunar eclipses, lunar occultations (including one of Saturn) and comets. Most important, he became extraordinarily skilled at the astronomical observations necessary for determining his local time, latitude and longitude. The…

In Under the Sky this issue, I want to feature a celestial wonder that I witnessed 50 years ago — at its all-around best in April 1970, it was what may have been the most beautiful comet of the 20th century. Enter Comet Bennett. At the time I had recently observed my first comet, Tago-Sato-Kosaka. I found this modestly bright object by myself with both naked eye and telescope in January 1970, the month after my 15th birthday. That was an incredibly thrilling and rewarding experience. But the March 1970 issue of Sky & Telescope soon arrived with a brief item announcing the approach of ‘Bright Comet Bennett’. Discovered at the end of December 1969 by accomplished amateur astronomer John Caister Bennett of South Africa, Comet Bennett (C/1969 Y1, or…

Last December, two interesting (but intrinsically faint) comets were found by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Hawaii. They are fascinating objects. The first, officially designated C/2019 Y1 (ATLAS) was discovered on December 16 as a fuzzy speck of magnitude 18. As further observations were obtained, an orbit was calculated which revealed a remarkable similarity with those of comets C/1988 A1 (Liller), C/1996 Q1 (Tabur) and C/2015 F3 (SWAN). The new comet therefore becomes the fourth member of what has become known as the Liller Group. Like the famous Kreutz Group, these comets are fragments of a single object that broke apart many years ago, possibly (although not necessarily) during an earlier perihelion passage. Having passed through perihelion on March 15, the comet is currently predicted to be…

Richer and denser than the Virgo Cluster and containing thousands of galaxies, the Coma Cluster (Abell 1656) is a telescopic wonderland that takes its name from its parent constellation, Coma Berenices. More than a hundred visible galaxies are packed into an area only a little greater than 3° in size; as many as 50 are visible through a 40-cm telescope. Exploring beyond its two dominant members is a challenge, though. At almost six times farther than the Virgo Cluster, its members are three or four times fainter. You can enjoy the sample tour I describe here with hardly more than a nudge of your telescope: The objects are contained in a single field of view of less than 1°. The Coma Cluster lies about 2.5° west of Beta (β) Comae…

Our region’s two major amateur astronomy conferences are only one and two months away, respectively, being the National Australian Convention of Amateur Astronomers (nacaa.org.au) — to be held in Parkes, NSW, on April 10–13 — and the Royal Astronomical Society of New Zealand’s annual conference (rasnz.org.nz), to be held in Wellington on May 8–10. Both events will see many experienced (and novice) amateurs gather to share their knowledge and experience through presentations and workshops, and meet up with friends old and new. If you’ve not been to either event and you have the opportunity to go, you won’t be disappointed if you turn up and take part. Those two events will be backed up over the following months by several astrofests and star parties: the Astronomical Society of NSW’s annual…