Indholdsfortegnelse for February/March 2018 i Australian Sky & Telescope

TO BORROW SOME WORDS from the title of a famous book and movie, the adventure of amateur astronomy really is a ‘never-ending story’. Our cosmic vistas are essentially unlimited, even by aperture — for no matter what the size of our observing instrument(s), we can never hope to do more than just scratch the surface of all the planetary, galactic and intergalactic possibilities out there in the Universe. Which I guess is why many of us tend to specialise in one field or another, whether that be hunting faint fuzzies or scanning for comets. In 2018, there’ll pretty much be something for everyone. If you’re into the Moon, we’ll have two total lunar eclipses. If you’re into planets, we’ll have the opposition of Mars in July (the best one in…

THE DWARF PLANET 136108 Haumea briefly slipped in front of an 18th-magnitude star in January 2017. Observers at a network of 10 observatories across central Europe recorded the event, discovering something unexpected: A ring encircles this little world. Haumea, which orbits in the realm beyond Neptune, was already a well-known oddball. It’s among the largest objects in the Kuiper Belt, has a highly elongated shape, spins rapidly, and possesses two moons. Now, several observing teams have detected a ring via secondary dips in the star’s light roughly 2 minutes before and after the main occultation. The ring is dark, narrow (70 km wide) and dense enough to block half the star’s light. The ring appears to lie in Haumea’s equatorial plane, which is shared by the larger, outer moon Hi‘iaka.…

Cassini’s Saturn surprises Scientists have explained some of the insights they gained during the unprecedented scrutiny offered by the Cassini spacecraft’s ‘Grand Finale’ orbits of Saturn. Those last orbits sent the spacecraft dashing at 35 km per second through a planet-ring gap about 2,400 km wide, giving Cassini the chance to directly sample the chemicals present in Saturn’s uppermost atmosphere. In theory, material is leaking from the innermost threads of the water-ice ring and drifting toward the planet. But the craft’s instruments swept up many heavier compounds, which might include methane and carbon monoxide — gases that would be chemically out of place in the water-ice rings, and shouldn’t be percolating up from the atmosphere either. Cassini also gave mission scientists a chance to examine the rings in extreme detail,…

About 290 million years ago, a volcano erupted in what is now eastern Germany. The blast lifted trees straight out of the ground and coated them with liquid rock. Beneath this debris, an entire forest fossilised. Last year, scientists studied rings from these ancient trees — but not to learn about Earth. They wanted to learn about the Sun. To the naked eye, the Sun looks like a uniform whitish sphere. But the solar surface is often mottled with dark spots, like the peel of a ripe banana. These sunspots emerge, live for a few hours or days (or longer), and then decay. Occasionally, 150 or more spots dot the solar surface. During those times, we observe many eruptions of high-energy radiation and, sometimes, superheated material, which can blast through…

• The outer atmosphere comprises molecular hydrogen with layers (from top to bottom) of ammonia clouds, ammonium hydrosulfide and water. Zonal flows (the belts and zones) characterise the large-scale dynamics, accompanied by small-scale vortices and turbulence. • The deep atmosphere extends about 300 km below the clouds. Microwave data suggest a separate flow regime, decoupled from the belts and zones above. • The weakly conducting molecular shell lies above the magnetic-field-creating mantle, but it might be coupled to the magnetic field if its zonal flows are strong. The top of this region is defined by where the zonal flow weakens to less than about 1 metre per second. This is also roughly where the diffuse ‘rock clouds’ of silicate molecules form. May extend down to about 2,000 km (the upper…

THE ESSENCE OF THE SUMMER SKY is the Orion Nebula. It’s the most observed, photographed and sketched object of the season simply because it’s one of the most beautiful and rewarding deep sky objects of them all. Look up on a dark, transparent night and there it is, glowing softly in the Sword of Orion. Located around 1,400 light-years away, it consists of matter only about 2,000 times the mass of our Sun. It’s the closest bright H II region — clouds, or nebulae, of ionised interstellar atomic hydrogen. Composed of a thin bubble of photoionised gas flowing from the much larger Orion Molecular Cloud, the Orion Nebula (M42) is roughly centred on Theta1 (θ1 ) Orionis C, a massive O7-type star, which, at magnitude 5.1, is the brightest member…

AN ANALEMMA is the figure-eight pattern the Sun makes in the sky when photographed at the same time periodically throughout an entire year. It’s a visual representation of the way the Earth’s axial tilt and orbital eccentricity interact during a trip around the Sun. It’s also very difficult to photograph. To get a pleasant spacing between Sun images, you need to take a photo at least once per week. That’s more than 50 shots, and every one of them has to be just right. For starters, you need to aim the camera at exactly the same spot in the sky for every shot. That means either building a dependable mount where you can set the camera each time and know it’s pointing at precisely the same place, or mounting the…

WHEN THE PAN-STARRS 1 telescope atop Haleakala on Maui swept up a 20th-magnitude object on October 19, observer Robert Weryk (University of Hawai‘i) noticed right away that its motion didn’t make sense. Orbital computations soon showed that it had passed within 0.26 astronomical unit (38,200,000 km) of the Sun on September 9. But its extreme orbital eccentricity, 1.19, meant that it is following a hyperbolic trajectory that’s not bound to the Sun. For the first time, observers had spotted an object visiting from interstellar space. At first astronomers suspected it was a comet, so the International Astronomical Union’s (IAU) Minor Planet Center (MPC) applied the designation C/2017 U1. However, when even the deepest telescopic images revealed no hint of a coma or tail, they decided it must be asteroidal, so…

A SUPER-LONG SUPERNOVA has astronomers reaching for new explanations of stellar explosions. In a typical core-collapse supernova, the inner collapse occurs so quickly that infalling layers of stellar material rebound off the core, driving a shock wave that sends much of the star flying outward. The expanding outer shells of ionised hydrogen glow for roughly 100 days before beginning to fade. Iair Arcavi (Las Cumbres Observatory) and colleagues thought they were seeing a typical core-collapse supernova when the Intermediate Palomar Transient Factory (iPTF) caught the 18th-magnitude explosion dubbed iPTF14hls. But the supernova kept on going, not for 100 days but for almost two years, as reported in the November 9 issue of Nature. What’s more, it exhibited at least five distinct peaks in luminosity, including the initial burst. A look…

1 Start with a dipolar magnetic field. (This is a simplification.) 2 The Sun rotates faster at the equator than the poles. This differential rotation stretches out the field along the equator. (v is for velocity) 3 Solar rotation also twists the field into loops. When these loops poke up through the surface, we see them as sunspots. Sunspots usually appear in pairs, each with a north and south pole. (Note: The spot pairs are at an angle, and the higher footpoint has an opposite polarity as the hemisphere it’s in. Important!) 4 Most of the magnetic field cancels out quickly: Burbling plasma motions move sunspots around, and their magnetic field lines snap into new configurations. But these cancellations leave behind bits of magnetism. Think of them as sunspot debris.…

PHOTOGRAPHY OF LANDSCAPES under a starry sky is a unique art form that until recently, only a handful of imagers were doing. I remember going to the most popular spots within national parks at night, where I’d rarely encounter anyone with a camera and a tripod in the wee hours. Fast-forward to today, and this type of adventure photography has entered the mainstream, commonly featured in television and print advertisements hawking everything from smartphones to SUVs. The most amazing nightscapes are often a combination of careful planning and inspired work, with a hefty dose of luck. Still, many published nightscape images could be improved with additional attention during post-processing. It only takes a few steps to take a nightscape image from dull to dazzling, and these steps don’t require much…

VISIBLE LIGHT AND X-RAYS helped astronomers paint a detailed picture of the relativistic jet in V404 Cygni, a black hole star system. Poshak Gandhi (University of Southampton, UK) and colleagues employed NASA’s NUSTAR X-ray satellite and the super-fast UltraCam on the William Herschel Telescope in La Palma, Spain, to track emissions from V404 Cygni. The black hole tugs gas away from its stellar partner as they whip around each other, resulting in flares. In June 2015 V404 Cygni underwent the brightest binary outburst in the 21st century. Astronomers had previously monitored visible light from black hole systems, but they hadn’t been able to pinpoint its origin — the photons could arise in the gaseous disk that feeds the black hole, the stellar companion that feeds the disk, or the jets…

For many of us, the planet Jupiter conjures mental images of a giant ball with latitudinal bands of red and white all the way from pole to pole, with the most remarkable anomaly being the Great Red Spot. We’ve had little reason to question this scheme: The glimpses that previous spacecraft have caught of high latitudes looked stripey. But Juno changed that. Upon the spacecraft’s arrival at Jupiter in July 2016, its JunoCAM wowed us with the first views ever captured looking directly down at the poles. Above about 50° latitude, it turns out, the planet darkens and takes on a blue tinge. Images show spectacular eddies and a chaotic mass of jostling storms. Particularly intriguing is the fact that Jupiter’s polar regions are so different from Saturn’s. While rotation…

Each year, we scour the marketplace searching for what we consider to be the year’s most exciting new products. To make our list, a product should introduce new (or improve upon existing) technologies, provide a solution to an old problem, or simply deliver exceptional value. Our Hot Products list for 2018 includes a variety of gadgets ranging from mounts, cameras and accessories aimed at the growing popularity of robotic astronomy to items big and small for observers who love being out under a starry sky. As is often the case, this year some products caught our eye because of their exceptional value — equipment that offers features and performance at a cost well below that of similar items in the past. We hope you enjoy reading about these innovative products…

As described in our January issue, there’ll be a total lunar eclipse on the night of January 31–February 1, visible in its entirety from New Zealand and the eastern states of Australia, and most of it observable South Australia and the Northern Territory. Western Australia will miss the beginning of the event. February will see several planets in the morning sky, but Venus (mag. –3.9, diameter 9.9") will be lost in the glare of the Sun, and Mercury (mag. –0.6 at the start of February and falling to 2.3 by the end of March, 4.9") will visible only for the first week, only a few degrees above the eastern horizon before sunrise. Things won’t be much better for the pair during March, with the two inner planets now very low…

We first introduced the star L2 Puppis in our January 2013 issue. To recap: At around 200 light-years away, L2 Pup is the second-nearest evolved red giant to the Sun (behind R Doradus.) The light curve up until 1994 showed it to be a semiregular variable star with a range of 3rd to 6th magnitude, with a period of 140 days. 1994 marked the beginning of a major dust obscuration event, and the light curve currently ranges from 6th to 8th magnitude. But the story continues. June 2015 saw the light curve nicely poised at minimum, but there it stayed. One whole ‘cycle’ was spent at 8th magnitude, with the star not re-brightening until December 2015. The exact reason is uncertain at this stage. Recent study has revealed that L2…

Her lovely tresses glow with starry light; Stars ornament the bracelet on her hand, Her vest, in ample fold, glitters with stars, Beneath her snowy feet they shine; her eyes Lighten, all-glorious, with the heavenly rays. — Capel Lofft, Eudosia, 1781 The constellation Virgo is sometimes identified with Persephone, the beautiful daughter of the harvest goddess Demeter. In one version of her myth, Persephone was spirited away by Hades to make her his queen of the underworld. Demeter was distraught, and in her sorrow she abandoned her stewardship of the fruits of the Earth. Cruel winter reigned, crops failed and famine loomed nigh. Zeus, king of the gods, thought to return Persephone to her mother, but he was too late. Having taken food in the underworld, Persephone could not live…

Sky-Watcher Star Adventurer Mini Australian RRP: $379 skywatcher.com.au What We Like: One device can both track and pan cameras Polar-alignment scope included Wireless app allows for easy programming Excellent battery life What We Don't Like: No speed-ramping option for time-lapses Connects via Wi-Fi (not Bluetooth LE) Status readout requires Wi-Fi to remain activated Firmware updates require Windows computer WHENEVER I PRESENT workshops on astrophotography and time-lapse imaging, I always show off an array of devices for moving the camera while it shoots. When I display one of the specialised ‘motion controllers’ designed to pan a camera during a time-lapse, someone always asks, “Can it track the sky?” The answer is always, “No, sorry!” When I show a device that can track the sky for long exposures, the question is, “Can…

IN THE EARLY 1960S, when I was about 12 or 13 years old, my older brother brought home a book that described the amazing things one could see with a telescope. This slim volume included instructions for building a 15-cm reflector, which would show such wonders as the moons of Jupiter and the rings of Saturn. Ordinary people with ordinary tools could create it, the book promised. I’d thought telescopes were constructed by experts and very expensive, so I was fascinated by the idea of crafting one myself on the cheap. Together with the Edmund Scientific catalogue, this little book was all I needed to do some serious dreaming. My first telescope comprised a 25-mm objective lens, an eyepiece, and a tube made of black construction paper. I fashioned a…