Indholdsfortegnelse for July - August 2021 i Australian Sky & Telescope

MARS ONCE HAD ENOUGH water to fill a global ocean 100 to 1,500 metres deep. But scientists have had trouble explaining where all of it went. In the journal Science, graduate student Eva Scheller and advisor Bethany Ehlmann (both at Caltech) used a model of the Martian water cycle to show that most of it was trapped in water-loving minerals in the Martian crust. Water (H2 O) rarely contains a heavier form of hydrogen called deuterium, which has an extra neutron. Water on Mars has become heavier over the eons, and previous studies assumed this happened as water was lost to space. After ultraviolet light from the Sun broke apart water molecules, normal hydrogen atoms were more likely to escape the atmosphere than heavier deuterium. However, escape hasn’t explained all…

WHILE ASTRONOMERS generally agree that the Milky Way has four major spiral arms, what they look like is still an open question. This includes the Local Arm that we call home (which may or may not be an arm at all). Now, two recent studies of the latest data release from the European Space Agency’s Gaia mission, one led by Ye Xu (Purple Mountain Observatory, China) and the other by Eloisa Poggio (University of Côte d’Azur, France), have upgraded the Local Arm from a spur to a major spiral feature, if not quite to a full-size arm. In the journal Astronomy & Astrophysics, Xu and his colleagues picked out 9,750 stars of spectral type O to B2, massive and brilliant stars that are at most 20 million years old and…

ASK ASTRONOMERS WHAT A GLOBULAR CLUSTER IS, and they are likely to show you a picture of a glorious, dense ball of stars. These tight-knit stellar families hover like ancient swarms of bees around the Milky Way and galaxies like it, and they carry unique information about the conditions under which their host galaxy assembled in the early universe. For centuries, astronomers have attempted to figure out how globular clusters formed. While doing this work, we have historically made a distinction between sparser open clusters like the Pleiades and globular clusters. Open clusters typically contain 100 to 100,000 stars, with a chemical composition similar to the Sun’s; they are generally less than a billion years old and we usually find them in the disk of the Milky Way. By contrast,…

Winter is here, and although the starfields of the mid-year Milky Way are adorned with numerous nebulae, open clusters and asterisms, this time of year also has its fair share of globular clusters. Two outstanding winter globs are M4 and M80 in the head of Scorpius, the celestial scorpion. M4 sits just 1.3° west of Antares, the ‘rival of Mars,’ whose fiery glare is unchallenged in this part of the sky. It looks like a dim and hooded eye next to Antares, but at magnitude 5.4 it’s a naked-eye target under any decently dark skies. About 4° to the north-northwest of M4 you’ll find another winter globular, 7.3-magnitude M80. M80 might attract more attention if it weren’t overshadowed by its brighter neighbour. As it is, M80 is sort of relegated…

There are two southern showers of interest in July, and a less-well positioned northern one in August. First up we have the Southern Delta Aquariids, which are active from July 12 through to August 23 with a predicted maximum in the morning hours of July 30. This is one of the more dependable for showers for southern observers, with a zenithal hourly rate of around 25. Its meteors are of medium speed, usually white and mostly faint. Occasionally some will leave trains. The second shower is the Alpha Capricornids, which (active from July 3 to August 15) also peaks on the morning of July 30. You can expect to see perhaps five meteors per hour from dark skies. These meteors typically are slow-moving with long paths, and often produce fireballs.…

I recently perused a copy of the fifth edition of Le Ciel by French science writer and journalist Amédée Guillemin. Published in 1877, this profusely illustrated tome contains a beautiful lithograph depicting Saturn based on observations by Otto Wilhelm von Struve (1819-1905) in the autumn of 1851 at the Pulkovo Observatory on the outskirts of St. Petersburg. The most striking detail of the print is a well-defined division in the faint, tenuous C ring. Struve detected this feature three-quarters of the distance from the ring’s inner edge to its outer border using the observatory’s 38.1-cm Merz refractor at magnifications of 400x and 700x. This feat demonstrates the high optical quality of the best 19th-century refracting telescopes. He announced his discovery in the Memoirs of the St. Petersburg Academy of Sciences…

It’s great to see that more and more astro events are returning to the calendar as the year progresses. For instance, organisers have announced that the next Perth Astrofest will be held on November 13. Always a great event that attracts thousands of participants, the Astrofest is a genuine family-friendly affair that combines astronomy education with entertainment. Details at astronomywa.net.au/astrofest.html. Also in the west, the Mount Magnet Astro Rocks Fest is back on again, September 17 to 19. Now in its fourth year, this unique event combines land and sky through an interesting blend of geology and astronomy. Mount Magnet is northeast of Perth, in the middle of WA’s historic gold rush region. Go to astrorocks-mtmagnet.com.au for details. And still in the west, the Shire of Ashburton, in the Pilbara…

Exoplanets are one of the hottest topics in professional astronomy today. Less than three decades after scientists discovered the first worlds around other stars, we know of more than 4,300 planets outside the Solar System. Another couple thousand candidates await confirmation. The Transiting Exoplanet Survey Satellite (TESS; a NASA-MIT collaboration) is actively adding to that tally. Astronomers predict that once they’ve finished digging through TESS’s first two years of data, they’ll identify about 10,000 new exoplanets via the transit method, which measures the minuscule change in the brightness of a star as a planet traverses its disk. Thus far, astronomers have used this method to find about three-quarters of all known exoplanets. Not only does it tell us something about the planet’s size relative to its host star, it also…

A SUPERMASSIVE BLACK HOLE some 690 million light-years away tore apart a star — and may have created neutrinos in the process. The IceCube Neutrino Observatory in Antarctica detected a single high-energy neutrino on October 1, 2019. The tiny, ghostlike particle came from a region in Delphinus and packed a punch of about 200 teraelectron volts (15 times more energetic than what the Large Hadron Collider can produce). Robert Stein (DESY, Germany) and colleagues observed the area within hours using the Zwicky Transient Facility. They found the fading glow of a tidal disruption event (TDE), produced months earlier when a black hole 30 million times the Sun’s mass had shredded a star that ventured too close. To create a neutrino, a high-energy proton must slam into another proton or a…

JUPITER’S GREAT RED SPOT (GRS) has been shrinking ever since regular observations began in 1878, from about 48,000 kilometres across to its present width of about 15,000 km. But recent encounters with other storms shrank it further, leading some to predict the iconic spot would come to an end. However, new data and analysis by a team of amateur and professional astronomers revealed that those encounters also pumped up the Great Red Spot’s energy, likely extending its life. Between 2018 and 2020, a series of smaller oval storms battered the GRS at a greater frequency than before, distorting the storm’s shape and tearing ‘flakes’ off its edge. In early 2019, amateurs circulated an alert and began systematic observations to provide context to data from NASA’s Juno mission. Professional astronomers also…

THE LARGE MAGELLANIC CLOUD is a fuzzy smear in the Southern Hemisphere sky, a subject of early humanity’s myth-making. Over time, astronomers determined that it and its companion, the Small Magellanic Cloud, are two separate, smaller galaxies near the Milky Way. By the 1990s, they thought that the pair had spent several billion years making loops around our galaxy. But in the last decade or so, we’ve realised that this, too, is likely a myth. Our understanding of these neighbouring galaxies has undergone a revolution, one that has changed not only what we thought we knew about the Magellanic Clouds but also about our very own Milky Way. Although not a large galaxy, the Large Magellanic Cloud (LMC) shows signs of structure. It has at least one spiral arm, but…

LAST YEAR JUPITER PROVED an able guide to finding Pluto, but the gas giant has since moved on, leaving the dwarf planet by itself in the wilds of eastern Sagittarius. However, a distinctive asterism and several bright telescopic stars point the way this season. As long as your scope can dig down to Pluto’s magnitude of 14.3, with a careful approach you should be able to find this Holy Grail of astronomical challenges Under a dark sky, a 20-cm telescope should be up to the task. An excellent place to start is the small asterism called the Terebellum — four stars brighter than 5th magnitude in the shape of a kite with Omega (ω) Sagittarii at its peak. Use the charts above and a wide-field eyepiece to locate Pluto on…

In our May/Jun 2021 issue, I wrote that the new SWAN comet (2021 D1) discovered by Aussie amateur Michael Mattiazzo was of the Halley type with a period of 77 years, based upon orbital data published at the time. However, subsequent orbital determinations based upon more recent accurate positions has not confirmed this. An orbit recently published and based upon position measurements from February 28 until April 2, whilst confirming that the orbit is elliptical, yield a period of around 950 years! — still quite ‘short’ by cometary standards, but hardly in the Halley class. July will see the return of the short-period comet 15P/Finlay, an object that has given observers some surprises during its previous two apparitions. Discovered by W. Finlay at the Cape of Good Hope on September…

The asteroid vesta is thought to be the parent body of a group of meteorites known as the HED clan. But astronomers may now have uncovered yet another origin story — this one involving the minor planet 6 Hebe, which reaches opposition in southern Aquila on July 19. Hebe is a stony, main-belt asteroid that measures 205 km across. It’s also the suspected source of two classes of meteorites: The H-chondrites (the most common type found on Earth) and the related, but rarer, IIE irons. Not all scientists agree that Hebe is the primary source of H-chondrites, arguing that its craters are too small to have produced the volume of material found on Earth. But recent research indicates some of Hebe’s fragmental remains may have produced a small family of…

THIS OBSERVING PROJECT began to take root while I was examining Minkowski 3-6, a planetary nebula in Pyxis, when the telescope tracked into the foliage of my magnolia tree. After venting my initial displeasure, I noticed a southerly corridor in the sky on the other side of the magnolia, resulting from the recent removal of a neighbour’s tree. The opening was about 20° wide and reached from the top of the tree line to at least –45° in declination. Would it be possible to view some mid-southern planetary nebulae through this gap? I realised then that planning on working up and down by right ascension and timing my observations for when the objects are in the leafy window would make more sense than sticking to a particular constellation or working…

FOR NEARLY TWO DECADES ‘lucky imaging’ has been the tried-and-true route to recording the most detailed images of the Sun, Moon and bright planets. Key to the technique’s success is the use of high-speed video cameras that record as many frames as possible in a short period, along with software to cull, register and stack the sharpest of them. The resulting images often show more details than can be gleaned with the eye alone. Best of all, it’s fairly easy to do it yourself. QHYCCD, a Chinese manufacturer specialising in astronomical cameras for both deep sky and planetary imaging, recently announced a new high-speed model geared specifically to those with an interest in near-infrared imaging. The QHY5III462C is a colour CMOS camera with a 6th-generation, back-illuminated Sony IMX462 sensor, engineered…

Stephen Voss is a medical general practitioner and astrophotographer based on the South Island of New Zealand, and well known for his images of the Aurora Australis. What got you into astronomy? I grew up in a small rural town with dark skies in the lower North Island of New Zealand, so the night sky was always accessible to me. I have clear memories of viewing my first lunar eclipse from home in May 1975, an early evening event that didn’t encroach on the bedtime of an 8-year-old. Even at that age I was noticing patterns made by the stars, before I even knew what a constellation is. Orion’s Belt fascinated me. What was your first telescope set-up? My father had a very nice pair of binoculars that I recall…

TWO INDEPENDENT GROUPS have measured the Hubble constant, the universe’s current rate of expansion, and their results have deepened the tension in an ongoing controversy. Observations of the far-away (early) universe, particularly the cosmic microwave background emitted 380,000 years after the Big Bang, lead to a current expansion rate of 67 km/s per megaparsec. But near-universe observations point to a higher value of 73 km/s/Mpc. Adam Riess (Space Telescope Science Institute) has been leading an effort to tie Cepheid variables, a ‘standard candle’ typically found in nearby galaxies, to Type Ia supernovae, another standard candle that can be seen from farther away. Improving on previous work, Riess’s team combined precise distances from the Gaia satellite with Hubble Space Telescope brightness measurements of 75 Cepheids in galaxies hosting Type Ia supernovae.…

A RECENTLY DISCOVERED asteroid appears to be an Earth Trojan, orbiting a gravitationally stable area with only one other known occupant. Amateur astronomer Tony Dunn reported the potential find on January 26 via the Minor Planet Mailing List. Given the preliminary designation 2020 XL5 , the asteroid is a few hundred metres across and appears to be orbiting the L4 Lagrange point. Trojan asteroids occupy the gravitationally stable Lagrange points about 60° ahead or behind the planets in their orbits around the Sun. In theory, Trojan orbits should be stable around every planet except Saturn, in which case Jupiter’s gravity pulls them away. But Earth Trojans have proven difficult to find because they’re small and appear close to the Sun on the sky. Earth Trojan orbits can meander — relative…

ASK ANY ASTRONOMER — professional or amateur — what comes to mind when they hear the name Cassini and they’ll probably mention the Cassini-Huygens mission to Saturn, or perhaps Cassini’s Division, the largest of the many gaps in Saturn’s famous rings. But more likely than not, they’ll know few details about the life and accomplishments of 17th-century astronomer Giovanni Domenico Cassini. Co-naming one of the most complex and important space missions after Cassini is a clue that he must have played a highly significant role in the history of science. But why isn’t he mentioned in the same breath as Galileo and Newton? When we consider Cassini’s many important achievements, his relative obscurity seems all the more puzzling and unjust. From Italy to France Cassini’s life was that of a…

MANY WOULD-BE astrophotographers stay on the sidelines because they imagine good results can only be achieved with expensive, specialised equipment. While it’s true that better cameras and lenses generally yield better results, that doesn’t mean you can’t capture the night sky with gear you may have already. Let’s say your main camera is a recent-vintage DSLR (or other interchangeable-lens camera) and the ‘kit’ lens it came with. Could such a basic setup be a practical starting point? There’s no harm in at least trying — and you’ll probably be delighted by what you’re able to capture. Soaking up starlight Kit lenses often feature lightweight plastic construction and offer a zoom range of around 18 to 55 mm. Night-sky photography is all about gathering as much light as possible, but these…

A pair of oft-overlooked zero-magnitude stellar jewels shine low in the northern sky on July evenings. One of them, Arcturus, is in the northwest and starting to descend. Vega is approaching the meridian around 10:00pm. Both are the Alpha stars of their respective constellations. Vega dominates little Lyra, the Lyre, while Arcturus anchors the kite-shaped formation of Boötes, the Herdsman. These two stars offer an interesting comparison since they’re extremely close to each other in brightness. It’s difficult to judge which is the brighter just by looking. The precise magnitude of Arcturus is –0.05, while Vega is magnitude +0.03 — a difference of only 0.08. Even a very experienced variable-star observer isn’t able to reliably distinguish between stars less than 0.1 magnitude apart. What’s more, the lower a star is…

Most amateur astronomers observe primarily for recreation and enjoyment, while others like to get scientific and monitor variable stars, asteroid occultations, comets and so on. The latter have the chance to interact with our professional counterparts, and even sometimes get their names published in professional journals. Reading the latest research for this column on R Coronae Borealis stars I came across some of my own observations, along with those of hundreds of others, plotted in tandem with data from the Infrared Astronomical Satellite, Spitzer Space Telescope and the Herschel Space Observatory. The R CrB stars are prime targets for visual observers, with three of them — R CrB itself, V854 Centauri and RY Sagittarii — as bright as 6th and 7th magnitude. These hydrogen-poor, carbon-rich supergiants exhibit sudden fadings of…

GOOD THINGS COME in small packages. Tiny Scutum, the Shield, hosts the Scutum Star Cloud, a glittering condensation in the winter Milky Way. Unfortunately, the Shield can’t block light pollution. Viewed from my suburban backyard with lots of city lights in surrounding suburbs, the sky is not always the best. Yet I attacked the constellation and its famous Star Cloud anyway. For weapons, I chose my 120-mm f/7.5 apochromatic refractor on a Go To equatorial mount, and my 25-cm f/6 Dobsonian. The Go To mount works perfectly well, but I don’t mind aiming the Dob manually. Its 6x30 finderscope was all I needed for a successful Scutum star-hop. Wild ducks Occupying the northeast corner of the Scutum Star Cloud is a deep sky showpiece even my local streetlights can’t wreck:…

I LISTLESSLY ROLL the rubbish bin down the driveway, my eyes fixed low, aimlessly staring at the footpath ahead. I’m worn down from a long day at work, rattled from the drive home, and, despite the joy my wife and two kids bring me, uninspired for what lies ahead — another weeknight routine of making dinner, cleaning up, reviewing mail and preparing for tomorrow. I begin the walk back to the garage, my gaze lifting slightly, eyes tracing up the trunks of the trees that populate my backyard, until the leaves give way to the sky. Then I see them, just above the trees — Jupiter and Saturn, their glow starting to emerge from the fading twilight. I notice it’s an especially clear sky tonight, with the Moon nowhere in…