Indholdsfortegnelse for November - December 2020 i Australian Sky & Telescope

JUPITER COULD HAVE around 600 moons measuring at least 800 metres in diameter, according to a team of Canadian astronomers. Most of the moons are in wide, irregular and retrograde orbits. Over the past 20 years, astronomers have found dozens of small Jovian moons thanks to technological advances with large digital cameras. Back in 2003, Scott Sheppard (Carnegie Institution of Science) had already estimated that the number of irregular moons larger than a kilometre would probably be around 100. Now, Edward Ashton, Matthew Beaudoin and Brett Gladman (University of British Columbia, Vancouver) have detected about four dozen possible new Jovian moons that are even smaller. Extrapolating from the sky area they have searched (about one square degree), they conclude that there could be some 600 of these tiny objects orbiting…

November is a month to celebrate those relatively rare celestial events known as ‘transits,’ the passage of Mercury or Venus across the face of the Sun as viewed from Earth. During a transit, the planet in question looks like a tiny black dot, slowly crawling across the solar disk. Transits were conceivable under the old ‘geocentric’ model of the Solar System, which had the Sun, the planets and the rest of the universe circling a stationary Earth. But that model did not allow for transits to be predicted. By the early 17th century, the geocentric model had been replaced in the minds of most astronomers by the heliocentric, or Sun-centred, model, championed by Copernicus and Galileo and refined by Kepler. Using this model, astronomers could now anticipate the movement of…

Approaching the Sun takes more energy than leaving the Solar System altogether, as any spacecraft leaving Earth inherits its orbital speed of 30 km/s (107,000 kph). Slowing that momentum counterintuitively takes more energy, says mission designer Yanping Guo (Johns Hopkins University Applied Physics Laboratory). “The launch energy required to reach the Sun is more than 50 times that required to reach Mars and twice that to reach Pluto.” When mission planning began, the best option for losing so much speed — a swing around Jupiter — was out of the question. A Jupiter flyby usually requires nuclear power, and NASA’s limited supply of plutonium-238 was already spoken for by other missions. For Parker to even begin development, it would need another way to the Sun. Guo realised that seven swings…

WHEN Late October 11 pm Early November 10 pm Late November 9 pm These are daylight savings times. Subtract one hour if daylight savings is not applicable. 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 curved edge 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 Canopus in the constellation Carina is about a third of the way between the south-eastern horizon and the middle of the chart. So if you look into the south-eastern sky,…

With the rich star fields of Sagittarius long gone with the winter, you might think that the opposite direction — the Galactic anti-centre — is bereft of interest. Not so! Towards the constellations of Auriga and Taurus, open star clusters, bright and dark nebulae and variable stars abound. Our nearest open star cluster, the Hyades, lies in this direction, as does the nearest large-scale star formation region, the Taurus-Auriga dark cloud. Our target this issue is T Tauri, the brightest of the proto-stars associated with that molecular cloud. T Tau was discovered in 1852 by asteroid hunter J. R. Hind when he noticed a 10th-magnitude star that was not plotted on his charts. Along with the new star an adjacent nebula was spotted, now known as Hind’s Variable Nebula or…

Mars reached opposition on October 13 and at magnitude –2.5 outshone nearly every other object in the night sky. With the Red Planet exhibiting a generously large disk of 22.4 arcseconds, observers have had a great opportunity to study its mysterious tapestry of dark and light markings for the weeks leading up to after opposition. Mars’ most prominent dark marking, Syrtis Major, was first recorded by the Dutch astronomer Christiaan Huygens on November 28, 1659. Later observers saw the same region as intensely blue-green and came to identify it as an actual Martian sea — a relic of perception that survives in other Martian nomenclature today. Astronomers once thought Martian seas held water and even displayed marked changes in their outlines over time. During the last decades of the 19th…

SHARPSTAR, A NEW BRAND in the astronomy market, is offering an attractive line of premium refractors and two unique reflectors specifically for astrophotography. The larger astrograph is the Sharpstar 20-cm PNT Newtonian, which offers a focal ratio of f/3.2 using a traditional parabolic primary mirror coupled with a coma-correcting lens. We tested the smaller reflector, a 15-cm f/2.8 Newtonian. The 150 f/2.8 HNT (Hyperbolic Newtonian Telescope) is designed specifically for imaging. While a supplied adapter enables an eyepiece to be attached, any eyepiece with a focal length longer than about 16 mm or so will produce a view with a dark shadow from the large secondary mirror floating in the middle of the field. This is not an instrument intended for wide-field views of the night sky. However, it does…

NO RADIO SIGNALS HAVE BEEN detected during a deep search for low-frequency transmissions emanating from a region in the direction of the southern constellation Vela. The volume of space covered by the survey — conducted with the Murchison Widefield Array (MWA) in Western Australia — is known to contain at least 10 million stars. The study was run by CSIRO astronomer Dr Chenoa Tremblay and Professor Steven Tingay, Deputy Executive Director of the International Centre for Radio Astronomy Research (ICRAR) and leader the Curtin University node of ICRAR. The MWA was employed to listen for radio signals at wavelengths similar to those used by FM radio stations. Any such signals would be suggestive of a non-natural source, or what astronomers call ‘technosignatures’. “The MWA is a unique telescope, with an…

SUPERNOVA 1987A WAS one of the most-observed supernovae in history after it exploded in the Large Magellanic Cloud just 168,000 light-years away. Telescopes around the globe and in space captured the blast wave, which illuminated three overlapping rings of material that had likely blown off in the star’s final years. But in the 33 years since, a puzzle has plagued astronomers. Neutrinos received at Earth right after the supernova indicated that the collapsed object ought to be a neutron star. But astronomers couldn’t find it. Dust obscures the centre of the blast, and some even wondered if the core had collapsed further into a black hole. Closer study showed the gaseous remains of the star’s outer layers to be slightly off-kilter, hinting that whatever compact object had formed in the…

The winners of the 2020 Central West Astronomical Society’s David Malin Awards were announced at a ceremony at Parkes, NSW, in July. The awards are named for, and the entries were judged by, renowned professional astrophotographer, David Malin. In addition, this year News Corp picture editor Jeff Darmanin selected a ‘photo editor’s’ choice winner. Congratulations to the category winners and well done to the runners’ up and all those who entered. You can see more images and several videos at https://www. parkes.atnf.csiro.au/news_events/astrofest/awards/2020_AstroFest_DMA.html…

POLAR FINDER Explore Scientific now offers a polar-alignment scope for its compact IEXOS-100 German equatorial mount. The IEXOS-100 Polar Finder and Adapter (US$89.99) is a small, focusable alignment scope with an etched reticle that shows the positions of stars near Sigma Octantis (and Polaris for the Northern Hemisphere) to help accurately align the IEXOS-100 mount. The device includes a mounting bracket that attaches to the front plate of the mount’s declination motor housing and can be folded underneath the motor when not in use. Explore Scientific also provides all necessary mounting hardware and a battery-powered, variable-brightness illuminator. explorescientific.com DEEP SPACE IMAGER Orion Telescopes & Binoculars adds a new camera to its line of deep sky detectors. The Orion StarShoot G16 Deep Space Mono Imaging Camera (US$1,279.99) features a 4/3-format,16.2-megapixel Panasonic…

Why in the world are we here? Surely not to live in pain and fear And why on earth are you there When you’re everywhere, Come and get your share. And we all shine on Like the moon, and the stars, and the sun. Yes, we all shine on, Everyone. — From the song Instant Karma by John Lennon In February, 1970, two months before the Beatles break-up became public, John Lennon composed, recorded and released his song Instant Karma in just 10 days. Fifty years later, the song seems especially relevant with the world in the grip of a pandemic and some countries experiencing social and political upheaval. Of course, the main astronomical reference in the song is the repeated chorus about humankind shining on “like the moon, and…

Catch Uranus at opposition See if you can spot it without telescopic aid. Uranus, will reach a milestone in the early morning of November 1, as it comes to opposition in a barren region of sky in southern Aries. At magnitude 5.7, Uranus is easy to spot through binoculars even from the suburbs. But the fact that so few stars populate the area in Aries will make this opposition ideal for a challenge attempted by few amateurs: finding the planet without optical aid. After all, from a rural sky it’s not too difficult to see stars slightly fainter than Uranus. Pick a night when there’s no Moon and when the planet is near the meridian. A particularly good opportunity comes in the third week of October after moonset. That’s when…

IMAGES WITH SOUTH at the top and west at left have long been the convention for drawings and photos of astronomical objects, as well as lunar atlases and maps of Mars intended for telescopic observers. A Newtonian reflector produces an inverted image, making comparisons with the eyepiece view straightforward — simply rotate the photo or drawing to match the view. Unfortunately, the image through a refractor or Cassegrain reflector (including Schmidt and Maksutov variations) equipped with a conventional mirror or right-angle prism star diagonal is erect but flipped left-to-right. This mirror-image reversal occurs in any optical system that reflects light an odd number of times. Righting the view Observers with refractors and Cassegrains can still enjoy an inverted image like those with a Newtonian reflector by removing the star diagonal…

FEW THINGS STIR THE SOUL like the sight of a comet airbrushed onto a dark starry sky, its ghostly glow intruding on a familiar celestial landscape, its tail blown by unseen winds, reminding us that the cosmos is far from static and fully known. The transience is part of the thrill. Comets travel through time as well as space. Short-period comets, which originate in the Kuiper Belt, beat a slow rhythm through our history. The most famous is 1P/Halley, which has a period of 76 years, roughly equal to the current average human life expectancy (which is twice what it was the last time the comet came around). In 1986, along with a group of fellow uni students, I trekked into the desert, pre-dawn, to observe Halley. I’m a big…

A TEAM OF RESEARCHERS LED by Jane Greaves (Cardiff University, UK) has announced the detection of phosphine in the cool cloud decks of Venus. Phosphine is a trace gas in Earth’s atmosphere associated with anaerobic life. Astronomers have previously observed it on Jupiter and Saturn, but its production there is understood to be driven by the gas giants’ high pressure, hydrogen-rich environments and intensely hot depths. On Venus, it could be a sign of something else entirely. Greaves and her colleagues observed Venus first with the James Clark Maxwell Telescope (JCMT) in 2017, then again with the Atacama Large Millimeter/submillimeter Array (ALMA) in 2019. They observed the planet at millimetre wavelengths and found the chemical fingerprint of phosphine — a molecule that many think could be a biosignature, or sign…

NEW RESEARCH SHOWS that stellar flybys are common in our galaxy’s crowded centre. Visits from interlopers could affect how young worlds grow in the Milky Way’s bulge. Moiya McTier (Columbia University) and colleagues conducted simulations of interactions between bulge stars over time. They found that over a billion-year period, roughly 80% of bulge stars would experience close encounters, passing within 1,000 astronomical units (a.u.) of another star. Half of bulge stars would have such an encounter not just once but more than 35 times over the course of a billion years. About a third of bulge stars could have company swing by within 100 a.u., and less than 1 in 5,000 stars entertain a visitor within 10 a.u. The new study takes into account both the crowded environs at the…

THE LAUNCH OF THE DELTA IV HEAVY sounded of fire and thunder. The rocket’s vibrations rumbled over the team of scientists and engineers standing kilometres away in the early hours of August 12, 2018, as they watched the rocket carrying NASA’s Parker Solar Probe climb into the sky. Team member Kelly Korreck (Center for Astrophysics, Harvard & Smithsonian) was tense. As the head of science operations for one of the mission’s instrument suites, she knew what to listen for from pre-launch vibrational testing — when one particular instrument mock-up had begun to rock violently. “In testing, we heard the Solar Probe Cup rattle, just ‘djr-djr-djr’ at one point in time when it hit a certain frequency,” Korreck says. “As I was listening to the frequency of the rocket taking off,…

CABLE UPON CABLE UPON TANGLED CABLE… Never had I seen such a convoluted jumble of wires, screws, pliers and other whatnots in such a small space. It was like a hardware store had imploded. In imploding, the mayhem had become strangely alive. I could feel the thrumming of the correlators in the pit of my stomach. A fan oscillated in the corner, whooshing breaths of air over the back panels of monoliths that looked like they belonged in the opening scene of 2001: A Space Odyssey. But that’s not where I was. I was in a radio telescope’s control room, an operations central reminiscent of the deck of the starship Enterprise. And mind you, this was a single-dish radio telescope, nowhere near the elaborate, multiple-dish setups of instruments such as…

If you weren’t convinced that you saw any trace of Earth’s shadow during previous penumbral eclipses, you should have no doubt as the November 30 event unfolds. At maximum eclipse, 83% of the Moon will lie in Earth’s outer shadow. I’ve struggled at first but eventually succeeded in seeing a trace of penumbral shading during previous eclipses, by carefully comparing the bright highlands along the Moon’s northern limb (the part deepest in shadow) with the highlands edging the southern limb. The shadow can betray its presence through a difference in tone between the two regions around the time of maximum eclipse. If you’re in New Zealand you’ll get to see the whole event, with the eclipse beginning shortly after the Moon rises above the horizon. But if you’re in Australia…

This year’s David Malin Awards attracted another fantastic range of images of all varieties of celestial objects (see pages 14–17). For the next 12 months you’ll be able to see the images in the flesh at the visitors’ centre at the Parkes Observatory in NSW, and a second touring exhibition will soon travel to selected venues beginning with Sydney Observatory. In the UK, the winners of the annual Insight Investment Astronomy Photographer of the Year competition have been announced, with Nicolas Lefaudeux taking out first place for his imaginative image of the Andromeda Galaxy. You can see all the winning images at rmg.co.uk/whats-on/ astronomy-photographer-year. In Adelaide, construction has begun on the Australian Space Discovery Centre and a state-of-the-art Mission Control Centre. The Australian Space Discovery Centre will be equipped with…

Jim Pollock has had a life-long interest in astronomy, and has been involved in amateur astronomy in Victoria for longer than he’d like to admit. As director of the Great Melbourne Telescope Section of the Astronomical Society of Victoria (ASV), he is heavily involved in the restoration of that classic telescope. What got you into astronomy? I remember as a child in the UK, observing a total lunar eclipse; it must have been in 1949 or 1950. At school, the day after the eclipse, we were taken into a darkened room and shown by the teacher, using a torch and two balls of different sizes, how the shadow of the earth obscured the Moon. It was a very effective demonstration, and one which I have never forgotten. In late September…