Innholdsfortegnelse for April 2017 i Australian Sky & Telescope

IT SEEMS LIKE ONLY yesterday that we embarked on the adventure of publishing Australian Sky & Telescope, launching into the local market with a magazine that is a blend of the best of the prestigious US edition and the best local knowledge of the southern skies. Now, 100 issues later, it’s safe to say that AS&T has become an invaluable part of the local astronomy landscape for educating and connecting amateur astronomers around our region. To paraphrase a famous saying, it takes a village to publish a magazine. We’re so fortunate to have the services of a stellar (excuse the pun) team of regular writers, both present and past, as well as a host of one-off authors, all of whom have helped make the magazine the success it is. We’re…

What is a black hole? A black hole is a pit in the fabric of spacetime. Space and time, according to Einstein’s theory of special relativity, are interchangeable parts of a thing called spacetime. Much as width, height and depth are dimensions of a box, so space and time are dimensions of spacetime. Although the dimensions of space and time are relative and can change, contracting or dilating depending on your frame of reference — an effect noticeable when dealing with strong gravity or relativistic speeds — units of spacetime are absolute. In this wacky landscape, a black hole is a cosmic pothole. Black holes are places where the density of matter grew so high that the outward pressure of the matter’s particles couldn’t withstand the inward pull of gravity,…

ONE OF THE JOYS OF OBSERVING from a high mountaintop in Chile is the panoramic view of the southern sky. As your eyes adapt to the darkness, the brightest stars appear first, then the fainter ones. The Milky Way arches overhead, and eventually you see two faint fuzzy patches of light near the south celestial pole — the Large and Small Magellanic Clouds. The LMC and SMC are the two largest galactic companions of the Milky Way, and the only two that are visible to the unaided eye. Over the past century, we have discovered several dozen dwarf galaxies around the Milky Way. The largest of these contain several billion stars, modest collections compared to the roughly 300 billion stars in our own galaxy. At the other end of the…

It is natural to assume that the elliptical nebulae are systems of many stars, whose great distance confines them to such a small area of the sky that their great multitude gives a pale, uniform glow, even though the light of each individual is imperceptible. The now well-accepted claim above isn’t a statement from early last century, when the possibility of external galaxies became a hot topic in the scientific community. Rather, this is a paraphrase of an astonishing conclusion drawn by Immanuel Kant in his 1755 Universal Natural History and Theory of the Heavens. Kant was one of the earliest proponents of this concept, and what a mind-blowing idea it is! It’s this knowledge that draws us out on starry nights to gaze at what Garrett Serviss called “small…

Are your lenses bedevilled by dust, fungus and other blemishes? Use these simple techniques to restore them to good-as-new condition. ALTHOUGH THERE ARE MANY correct ways to clean an optical surface, there are also many wrong ways. The best way is to keep the lens caps on whenever you aren’t using it! In this article, I’ll give you the benefit of my many years of experience servicing and repairing optics and provide some examples of both what to do, and what not to do. Take a look at my Top 10 tips in the sidebar on page 61 and be honest with yourself – how many of these rules have you broken over the years? If you’ve ignored all or some of them, you’ll be more than aware of what…

What We Like: Very good noise performance Built-in intervalometer In-camera star-trail stacking In-camera average-stacking What We Don't Like: Astrotracer only partially accurate Dark frame did not equal light frames Dim ‘Live View’ image Short battery life ASTROPHOTOGRAPHY is a niche market, and yet we have seen major camera manufacturers introduce DSLRs aimed at amateur astronomers. Its latest offering comes from Ricoh Imaging. Their new Pentax K-3 II contains innovative features of interest primarily to astrophotographers and unique to Pentax. We tested a unit on loan from Ricoh, along with a 14-mm f/2.8 SMC Pentax-DA lens, a popular focal length for nightscape and Milky Way photography. K-3 II’s unique features Unlike the recent ‘A’ model DSLRs from Canon and Nikon aimed at astrophotographers, the Pentax K-3 II does not have a…

AS AN ASTROPHOTOGRAHER who grew up in the days of hypered Kodak 2415 technical pan film and hand guiding, lived through the development of charged-couple devices, and revels in today’s fantastic images from advanced astrophotographers and satellites, I thoroughly enjoyed Breakthrough! 100 Astronomical Images That Changed the World. Like Galileo’s first revolutionary description of the view through a telescope, the coupling of a camera to a telescope led to a dramatic revolution of understanding. The common theme in both events is that each has changed our perception of the universe in some way. Breakthrough! is a marvellous history of imaging. Gendler and GaBany, who are well-known advanced astroimagers, start with the earliest forays into daguerreotypes and then detail the development of astrophotography over the past 175 years, all the way…

Fast radio burst has a surprising source FOR THE FIRST TIME, astronomers have placed a mysterious type of radio signal on the cosmic map — and it’s in a dwarf galaxy. The source, FRB 121102, was first detected in 2012 as a fast radio burst (FRB) — an ultrabright, ultrabrief burst of radio waves with mysterious, likely extragalactic origins. But unlike its cousins, which have only burst once before disappearing, FRB 121102 has flared up several times, making it the only one known to repeat. FRB 121102’s repetitions have caused trouble for theorists, because many thought that FRBs must be catastrophic, one-time events, like collisions between neutron stars or collapsing supernovae. That couldn’t be universally true if one were to repeat, as this one has; its source clearly survived. The…

WITH THE SKIES GETTING DARKER earlier and the weather cooling down nicely, it’s time to get our sky-watching hats on and look for some planets. The innermost planet, Mercury , though, will not be one of them this month. It begins April very low on the western horizon, and within weeks will be lost to view between Earth and the Sun. Next month will be better, when it will reappear in the east before dawn and climb up to a maximum of 26 degrees elongation from the Sun. Venus is back in our morning skies, out to the east, where it will remain all the way through until November. This month, the planet will reach a point called ‘greatest illuminated extent,’ making it ideal for observation. Take a look through…

Without rims, craters would just be holes in the ground. Rims provide visual drama. As the first rays of sunlight hit a majestic crater such as Copernicus, its elevated circumference brightly reflects the morning light — while the interior floor remains in inky blackness. A little later, as the Sun rises higher, we delight in long shadows dramatically cast across the floor by individual peaks along the enclosing rim. Craters form when mountain-size fragments of cosmic debris slam into the Moon’s surface. Their high velocity and great mass excavate huge volumes of crustal rock. This material is forcefully ejected, spreading debris near and far. In fact, fragments of lunar rock from the Copernicus impact probably lie buried in billion-year-old sediments here on Earth. Some ejecta, shot out of the forming…

When it comes to astronomical optics, prevention is much better than a cure… especially when the latter can mean a potentially expensive repair or replacement of your favourite instrument. So make sure you follow the author’s Top 10 tips for caring for your optics. 1 Keep the dust caps on. 2 If it looks reasonably clean, don’t clean it! 3 Keep your optical device in a protective case if it has one. 4 If you’re using your telescope, eyepieces or other optical device outside on a cold night, do not put the caps on immediately upon coming inside — allow the optics to reach thermal equilibrium with the room before doing so. 5 If it looks reasonably clean, don’t clean it! 6 Store it with silica gel (silicagel.com.au). Not just…

WHAT WOULD YOU GET if you took practically every convention in telescope making and stood it on its ear? Something that looks and functions remarkably like the ‘Dogson’ created by Craig Daniels. Craig didn’t set out to make the anti-Dob. His goal was to produce a simple-to-build, easy-to-use, modest-aperture scope that would break neither the bank nor the back of the person carrying it. He started with a 15-cm f/8.3 mirror. Why f/8? At long focal lengths a 15-cm mirror can remain spherical and still be well within 1/4-wave accuracy. And spherical mirrors are easier to make than parabolics. The ‘tube’ is a wooden box, which are easier to build than tubes or trusses. In order to keep the secondary mirror small and the upper end of the scope simple,…

RED SKY AT NIGHT Tim Bruton Taken from Smith’s Beach, Phillip Island, Victoria on January 27, this stitched, four-image panorama shows the glow of an aurora on the southern horizon. Tim used a Canon 6D camera, Sigma 24-105-mm lens at 24 mm and 30-second exposures. WETLANDS WONDERS Rene Martens While snapping some shots of the sky over the Winton Wetlands, Rene noticed a bit of a glow, and so turned his Canon 6D with Sigma 24-70-mm lens in that direction to secure this 15-second image. AN OLD FLAME Bo Li The famous Horsehead and Flame nebulae reside in Orion, everyone’s favourite summertime constellation. For this shot, Bo used a 110-mm scope and a full spectrum modified Canon 1100D camera. Exposures were 80× 120 seconds at 1600 ISO with equal dark…

Is the ‘brightest supernova ever’ a shredded star? Hailed as the “most luminous supernova,” the object dubbed ASASSN-15lh is still mystifying astronomers. It appeared to be the death of an extreme type of star, exploding with twice the brightness of any other known supernova, but then it threw researchers for a loop when it rebrightened. A new study by Giorgios Leloudas (Weizmann Institute of Science, Israel) and colleagues using the Hubble Space Telescope refines ASASSN-15lh’s location, placing it within 1,000 light-years of its host galaxy’s centre — and possibly in the centre itself. Paired with spectroscopic observations, the result suggests the burst might instead be the death of a star ripped apart by the galaxy’s supermassive black hole, the team argues in the December 12 issue of Nature Astronomy. But…

THE FIRST TWO EXOPLANETS discovered were truly alien. To begin with, they don’t orbit a star, but a pulsar dubbed PSR 1257+12 — a tiny, corpse-like remnant of a once mighty star, which rotates more than a hundred times per second. The pulsar blasts the planets with a stream of particles, which likely produces permanent aurorae that dance across their dark skies and polishes their surfaces until they glisten. But these oddities pale in comparison to the mass of the two planets — at three to four times the mass of Earth, these worlds have no parallel in the Solar System. After Earth, the next widest planet in our system is gaseous Neptune, which is nearly four times larger than Earth and has 17 times more mass. (Uranus is a…

THE ETA AQUARIDS IS ONE of the best meteor showers visible from southern skies. Like the Orionids in October, it is associated with Comet 1P/Halley. This shower starts around April 19 and goes until May 28, but with a relatively broad maximum — sometimes with a variable number of sub-maxima — that occurs around May 5/6. The meteors are often fast and bright, making the wait for the radiant to rise worthwhile. Many of them leave persistent trains, some lasting for minutes. They are usually yellow, but orange and blue are often seen. The average magnitude is 2.7, and fireball and bolide active is usually minimal. International Meteor Organisation (IMO) analyses based on data collected between 1984 and 2001, have shown that hourly rates are generally above 35 in the…

AUSTRALIA’S BIGGEST ASTRONOMY festival is on again. The WA Astrofest will be held in Perth from 5.30pm to 9.30pm on March 18, at Curtin Stadium, Curtin University, next to Edinburgh Oval, Bentley. This free event is great family fun, enabling astronomy enthusiasts, young and old, to discover the stars, telescopes and science in general. There’ll be 50-plus telescopes to look through, special guest presenters, hands-on activities for kids, an astrophotography exhibition, portable planetaria, rocket launches and information exhibits. Special solar viewing will be available on the oval, finishing at 6pm. The Star Wars 501st Legion Garrison and Rebel Alliance characters will be back in full force, and they’ll bring their Tie Fighter and Dr Who Tardis too. Stallholders from 20-plus organisations will be there to help attendees discover more about…

What we’ve learned about Mars NASA’s Curiosity rover has found evidence of long-gone habitable environments on the Red Planet. Spirits of our galaxy’s past Streams of stars in our galaxy’s dark matter halo are raising questions about the Milky Way and its past. Narrowband nebulae Create your own colourful nebulae images with a brilliant new software technique. Disintegrating planet As astronomers watch, a world that came too close to its dead star is slowly falling to pieces.…