Indholdsfortegnelse for March - April 2021 i Australian Sky & Telescope

OUR SENSE OF SIGHT is perhaps the most precious of our senses. It not only enables most of us to function in the everyday world, it also lets us experience the wonder of the universe in which we live. For those of us who have sight, imagine if we couldn’t see the Moon or a meteor, a galaxy or a nebula, or simply the amazing starfields of the Milky Way? Imagery has opened our eyes to the splendour of the cosmos and all that’s in it. And of course it’s one of the primary scientific tools for understanding all of the processes that began and continue to guide the evolution of all that is out there. And how marvellous it is that we live in an age when amateur astronomers…

It might seem a silly question, but astronomers aren’t certain Orion’s red supergiant will have a spectacular demise. Observations haven’t turned up clear examples of supernovae from red supergiants born with more than about 20 solar masses. (Betelgeuse is potentially below that limit, but astronomers don’t know for sure.) It’s possible stars above the limit instead implode directly into a black hole, perhaps due to how the star burns its carbon. Alternatively, the larger stars might lose enough material as they age that they evolve into hotter yellow or blue supergiants before exploding.…

One of my favourite objects in Monoceros, the Unicorn, is the open cluster NGC 2232. You’ll find it 2° north of Beta (β) Monocerotis, which is itself a fabulous multiple star to revisit with a telescope. At magnitude 4.2 and almost a degree across, NGC 2232 is big, bright, and shows interesting detail even at binocular magnifications. In particular, look for the 5th-magnitude star 10 Monocerotis near the centre, with lobes of stars extending to the northwest and southeast. We can see this level of detail because NGC 2232 is fairly close as open clusters go, just a little more than 1,000 light-years away. It is also a young cluster, between 25 and 30 million years old. That’s almost half of the time that separates us from T. rex, but…

For most of the hours of darkness during March and April, the sky will be largely devoid of bright planetary targets, with Mars being the sole exception. Let’s take a look at what we can expect to see. Mercury (mag. 0.0, dia. 6.3”, Mar. 15) can be seen in the eastern sky before dawn, poking its head over the horizon about an hour and a half before sunrise at the beginning of March. The planet will form a tidy grouping with Jupiter and Saturn, with Mercury and Jupiter having a very close (0.5°) encounter on the 5th and 6th. The latter date is also when Mercury reaches its point of greatest western elongation (ie. angle from the Sun), after which it will begin to descend into the dawn twilight and…

The International Space Station is often one of the brightest objects in the night sky. Many of us enjoy its regular appearances during morning and evening twilight when it passes silently across the sky, ferrying its human cargo at more than 27,600 kilometres per hour. For current pass times tailored to your location, go to heavens-above.com or grab a free app such as ISS Spotter (iPhone) and ISS Detector (Android). Much less frequently, the ISS transits across the face of the Moon or Sun. Such events are quite rare because the disks of the Moon and Sun are only 0.5° across. As a result, the track of visibility is a narrow one that requires the observer to be in precisely the right spot at the right time. Thanks to the…

ON A TRIP TO SOUTH AMERICA a year or so ago, Robert Capon made the decision to travel light, leaving his portable telescope at home. That was a mistake, as all he had to appreciate the sky was his 8x42 binoculars. He did take his carbon-fibre trekking poles, though, and while hiking began to wonder if he could design a travel scope that would use the poles for struts. The goal was to build a portable scope that he would never be tempted to leave behind. So he settled on a 114-mm f/4 mirror, which would just fit into a Pelican 1120 Protector Case. The case is lightweight yet rugged, and the plastic is easy to drill and shape with a Dremel tool, plus it holds screws well. Mounting the…

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Every year the Auckland Astronomical Society holds the Harry Williams Astrophotography Competition, and each year it attracts the most amazing photos from some very talented astrophotographers, each of them sharing their views of the cosmos as seen from under New Zealand’s pristine dark skies. On these pages we present just a taste of some of the winning imagery, as judged by world-renowned photographer, Babak Tafreshi. You can see the full set of winning images at astronomy.org.nz. Australian Sky & Telescope is proud to be a sponsor of the competition.…

WHEN Early March 10 pm Late March 9 pm Early April 8 pm Late April 7 pm 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.…

There are only two minor southern meteor showers of note for March and April. The first is the Gamma Normids, active from late February through until late March with a maximum of sorts around March 14. The word ‘active’ is probably a bit misleading — don’t expect to see too much, as the International Meteor Organisation is predicting a zenithal hourly rate of just 6. Nonetheless, it’s worth taking a look in the hours prior to dawn on the 15th, especially as there will no interference from moonlight. The other shower is the Pi Puppids, notable for being produced by the comet 26P/Grigg-Skjellerup. This shower is active (in the same sense of the word) from April 15 to 28, with a maximum on the 23rd. Pi Puppid meteors tend to…

When we look up into the night sky each star has its own story, each is at a different stage in its life. If we are very fortunate, as with Supernova 1987A, we may find ourselves in the right time and place to witness a massive star announce the end of its life with great fanfare. The last supernova visible to the unaided eye in our own galaxy was in AD 1604. These events, albeit rare, require little effort on the part of the observer. Indeed, some are hard to miss, such as the AD 1054 supernova that resulted in the Crab Nebula — that stellar explosion was visible in daylight for weeks after the event. Conversely, observing stars at the beginning of their lives takes great effort, as they’re…

Aussies who have a passion for astronomy and who share that passion by communicating astronomical discoveries and research with the public, are eligible to put their names forward for the prestigious David Allen Prize. Named after the late Dr David Allen (read his obituary at http://adsabs.harvard.edu/full/1994Obs...114..250M),who worked at the then Anglo-Australian Observatory, the prize is awarded roughly every three years by the Astronomical Society of Australia (ASA) for “the best contribution, or series of contributions which portrays an astronomical theme in an exciting and educative way”. That contribution must have been undertaken in Australia within the past three years, and only Australians are eligible to apply. According to the ASA, “The scope of the activity can be quite broad such as public presentations, popular writing, sustained media and outreach events,…

Streetlights and pollution A study led by Christopher Kyba (GFZ German Research Centre for Geosciences) shows that while streetlights are an important source of light pollution, they’re far from the only culprits. The city of Tucson, Arizona, has connected more than 19,000 LED streetlights in a ‘smart city’ control system. From March 29 to April 7, 2019, Kyba and colleagues manipulated public lighting in Tucson, then took overhead images using the Suomi National Polar-orbiting Partnership satellite. They found that Tucson’s streetlights contribute less than 20% of light escaping to space; the rest comes from other light sources such as carparks and billboards. Tucson’s streetlights have full cut-off shielding, which gives the city darker skies than most; nevertheless, the study, published October 28 in Lighting Research & Technology, suggests that fixing…

Most T Tauri stars are young pre-main-sequence stars that were born within the last several million years and are less than 2.5 times as massive as the Sun. T Tauri itself, however, may be an even younger variety of star, called a protostar. Despite their similar names, the two stellar types — protostars and pre-main-sequence stars — are different stages of stellar evolution. A protostar forms after a clump in an interstellar cloud rapidly collapses under the force of gravity. Gravity causes material to crash down toward the object’s surface, heating it so much that it begins to emit light. Thus gravity — and not nuclear fusion — powers the newborn star. New material from the birth cloud keeps raining down onto the protostar, increasing its mass. In fact, the…

MARCH 2 Moon 7° north-east of Spica 3 Mars 2.7° south of the Pleiades 5 Moon 6° north-west of Antares 6 Jupiter 0.5° south-west of Mercury 6 Mercury greatest elong. west (27.3°) 10 Saturn 4° north-east of the Moon 11 Jupiter 4° north-west of the Moon 11 Mercury 5° north-east of the Moon 19 Moon 8° north-west of Aldebaran 20 Equinox 23 Moon 3° south of Pollux 23 Mars 7° north of Aldebaran 26 Venus in superior conjunction 26 Moon 7° north-east of Regulus 30 Moon 7° north of Spica APRIL 2 Moon 6° north of Antares 6 Saturn 9° north-east of the Moon 7 Jupiter 8° north-west of the Moon 16 Moon 7° north of Aldebaran 17 Mars 2° east of the Moon 19 Mercury in superior conjunction 19…

In astronomy, the main sequence is the continuous band of stars spanning the Hertzsprung-Russell diagram, which plots stellar colour and intrinsic brightness. When a large main-sequence star runs out of hydrogen fuel, it becomes cooler, redder and radically expands in size as it moves off the main sequence. Unlike stars, impact craters do not dynamically evolve. But, based on size and morphology (ie. shape or form), they often have parallels to the distribution of stars on the H-R diagram. For example, one can consider the main sequence of impact craters as the systematic morphological difference from small conical pits such as the 13-km-diameter crater Chladni, to mid-sized craters with partial wall collapses as seen in 24-km Lalande, and on to large craters with terraced walls and central peaks, like 96-km…

No other family of proplyds has yet been identified outside M42. The best-known correlate might be M16, the Eagle Nebula in Serpens, first observed in detail with the Hubble Space Telescope in 1995. In what some have voted to be Hubble’s most beautiful and iconic image, the ‘Pillars of Star Formation’ host stars at the end of thin stalks, protostars whose birthplace has been whittled away. In 1999 I used my 63.5-cm reflector to observe two of these Evaporating Gaseous Globules, or EGGs. The Rosette Nebula is an example of a region of ionised hydrogen that has been carved out by strong stellar winds, similar to the environs of Theta1 C Orionis. In the Rosette Nebula, the star’s circumstellar disk was dissipated in only 1,000 years by the powerful radiation…