Indholdsfortegnelse for July - August 2020 i Australian Sky & Telescope

Astronomers naturally revel in the dark, yet for hundreds of years the disciples of the night sky have watched it disappear into a haze of light pollution. As the tentacles of urbanisation and artificial light encroach on even the darkest observation footholds in the world, we can no longer solve the problem simply by moving observatories from one remote place to the next. The Southern Hemisphere has been slow to catch on to the dark sky trend that has been growing rapidly in countries north of the equator. The USA, Germany and Italy are leading the way with the publication of scientific research not only on the impact of artificial light, but also on the technologies that might help to reduce that impact. But the Australasian Dark Sky Alliance (ADSA)…

Based on the chemical patterns in the oldest Population II stars, astronomers have suggested several possible ways the universe’s first stars died. MIXING-FALLBACK: As the core explodes, the gravity of the newly formed neutron star/black hole drags on expanding ejecta, causing it to fall back and mix. The star ejects large amounts of carbon and oxygen, but elements heavier than silicon mostly end up in the compact remnant. PULSATIONAL PAIR-INSTABILITY: Stars lose their outer layers over time and in a series of pulses, ejecting carbon, oxygen and elements of similar atomic mass. Heavier elements are trapped in the core when it collapses. ASYMMETRIC, ROTATING: A rapidly spinning star explodes, and the energy and spin power jets that emerge from the core. The jets carry zinc and some iron up into…

ENHANCED OBSERVING Explore Scientific now provides a complete observing package with its FirstLight 203 Newtonian with EXOS2GT GoTo Mount (US$1,099.99). This 20-cm f/4.9 Newtonian reflector features a sturdy 2½-inch Hexagonal rack-and-pinion focuser with extended travel to ensure that most any eyepiece can come to focus. Its EXOS2GT German equatorial Go To mount uses belt-driven stepper motors to yield smooth tracking of celestial objects. The StarTracker hand paddle includes 1-, 2- and 3-star alignment routines and an internal database of more than 270,000 objects powered by eight D batteries. The telescope comes with 2-inch and 1¼-inch eyepiece adapters, a 25-mm 1¼-inch Plössl eyepiece, a red-dot finder, a universal smartphone camera adapter and two 5-kg counterweights. IMAGING PACKAGE Software Bisque announces a new software package for advanced astrophotographers. TheSky Imaging (US$595) includes…

This issue’s variable star is U Scorpii. Like our May issue’s target, T Coronae Borealis, U Sco is a recurrent nova. (If you have the May issue handy, give it a quick re-read.) U Sco has a period of 10.6 (±1.6) years between explosions, and it turns out the next one is due around now. However, Brad Schaffer of Louisiana State University, who predicted the 2010 event, says there are indications it might be early. Let’s hope we’re not too late. Beyond the nova explosion is the supernova. U Sco, like T CrB, contains a white dwarf that is already close to the 1.4 solar mass limit that it needs before exploding. A survey of the literature suggests that U Sco is possibly the best thermonuclear supernova candidate known, with…

Stargazers are in for a treat this winter, with three planets — Jupiter, Saturn and Pluto — all reaching opposition within a week of each other. Or to be more politically correct in this day and age, it will be two planets and one dwarf planet. Jupiter will reach opposition on July 14, Pluto on the 12th and Saturn on the 21st. Opposition is when a planet and the Sun are on opposite sides of the sky as seen from the Earth, and is usually considered to be the best time for observing as the target is visible all night long from sunset onwards. Fortunately for observers at mid-southern latitudes, Jupiter, Saturn and Pluto will be well placed for viewing due to their southern declinations — all of them can…

FIFTEEN YEARS AGO, I was bored with amateur astronomy. I was tired of seeing deep sky objects — galaxies, nebulae and star clusters — as nothing more than faint blobs from my backyard. I wanted to go deeper into the night sky, too, to see more of everything, whether from home or from dark sites. A telescope larger than my 20-cm would have helped, but I didn’t want to haul around a monster-sized Dobsonian reflector, much less pay for one. Not long after my observing sailed into the doldrums, I found myself at an amateur astronomy conference. The sky was more orange than black from thousands of streetlights surrounding our hotel. Yet, one brave enthusiast set up his telescope anyway to take us on a video tour of the sky.…

Is interstellar comet 2I/Borisov breaking up? THE INTERSTELLAR COMET designated 2I/Borisov, discovered on its way into the Solar System in 2019, began shedding chunks in late March — more than three months after its closest approach to the Sun. Two analyses of Hubble Space Telescope images taken between March 23 and 30 show fragments drifting from the comet. Analysis of the images shows a small piece of the comet breaking off and floating slowly away, David Jewitt (University of California, Los Angeles) and colleagues found. The fragment was bright and only 180 kilometres from the comet’s core at the time Hubble took the images. What’s more, after processing the same Hubble images to increase the contrast between the core and the coma around it, Bryce Bolin (Caltech) and colleagues spotted…

I work in the pathology industry, which, to the surprise of many, experienced a significant downturn in workload in April 2020 due to the COVID-19 crisis. As a result I grabbed the opportunity to take some time off work, and ‘lockdown’ gave me the chance to concentrate on my hobby, astronomy. And in the process I discovered a comet. As per International Astronomical Union naming guidelines, C/2020 F8 (SWAN) is not named after me as I did not use my own equipment. I found C/2020 F8 by searching data publicly available on a website of the Solar and Heliospheric Observer (SOHO) mission. The SWAN (Solar Wind ANisotropies) instrument is an ultraviolet camera aboard the SOHO spacecraft. SOHO has been in operation since 1996. Its primary purpose is to study the…

Astronomers, like most scientists, love to classify things. It was in this spirit that Walter Baade introduced the idea of stellar populations in the 1940s. He noticed bluer stars, which he called Population I, congregate in the spiral arms of the Milky Way and other galaxies, while redder Population II stars were found in and around the bulge of the galaxy, in the halo and in globular clusters. Population I stars stay in the disk as they orbit the galactic centre along fairly circular paths, while Population II stars in the bulge and halo can in some cases follow highly elliptical orbits around the centre of the Milky Way and can shoot through the disk as well. In the early 1950s, astronomers found Population I stars had much larger abundances…

It seems to me that Ophiuchus often gets a low rating from beginners for its supposed lack of observational thrills. It’s true that the star pattern of the Serpent Bearer is big but rangy, with a large centre that has no bright stars. And though the constellation’s globular clusters are amazingly numerous, they’re smaller and dimmer than the mighty globular blazes in neighbouring Serpens, Scorpius and Sagittarius. Perhaps it’s true that Ophiuchus doesn’t offer the brightest splashy wonders for small telescopes and novice observers, but the incredible variety of its attractions can help improve a beginner’s observing skills and lead to a greater awareness of the diversity of deep sky objects in the heavens. Diversity? In out next issue we’ll explore the constellation’s collection of globulars, its two huge open…

Grab all the Mars you can this apparition. The Red Planet won’t be this close to Earth again until 2035. Closest approach during the current apparition will occur on October 7, when the tiny orb will swell to 22.6”. That’s only 1.7” less than at its perihelic opposition in 2018, which was favourable for Southern Hemisphere observers due to the planet’s southerly declination. This time Mars will stand 31° farther north — at declination +5° — but that equates to a still favourable altitude at culmination at 1:30am on October 7. As seen from mid-southern latitudes one hour before sunrise, the planet stands some 56° high in Aquarius on July 1. During the month, its ruddy disk will grow from 11.4” to 14.6”. Longtime Mars observers know that every arcsecond…

DREW SORENSON is a refractor nut. He’s also an amateur telescope maker. So, not surprisingly, he’s made several refractors, his largest being a 150-mm f/10 with lenses he ground himself. Drew contacted me after he read my article on ‘hobby killers’ (AS&T: Feb/ Mar 2020, p. 36). He said, “I am very frustrated to hear so often that people don’t consider larger refractors because they would need a mount that would cost over $1,500. I think the hobby is at least ‘stunted’ (maimed?) when people don’t think they can enjoy what refractors can contribute visually because of lack of an expensive mount.” And he showed me a mount that costs about $125 in parts and works like a charm. Back in the early days of amateur telescope making, nearly every…

Every two years, Australia’s professional astronomers bestow the Berenice and Arthur Page Medal on an amateur astronomer who has made significant scientific contributions in the field. The Medal is named in honour of a husband-and-wife amateur team who were active in astronomy from the 1960s onward, and who were members of the Astronomical Society of Australia (ASA). This year, the ASA has awarded the Medal to TG Tan. Tell us about the Perth Exoplanet Survey Telescope Observatory The PEST Observatory is an off-the-shelf telescope in a homemade plywood shelter located in my backyard. With it, I do high-precision observations for discovering new exoplanets. Exoplanet discovery is a team sport requiring many different skills and much bigger telescopes, so I work with teams of, mainly, professional astronomers. The main collaboration at…

Mars has always held a fascination for inquiring minds, and has been a major focus of attention for space exploration over most of the 70 years of the Space Age. Flyby missions and orbiters were sent to the planet in the early years, and the first robot landers — the two Vikings sent by the US — touched down in 1976. But to explore the planet properly and winkle out its secrets, we needed to be able to move around and not be limited to distant views from orbit or a fixed location. That capability finally came more than 20 years after the Vikings, with the arrival of NASA’s Mars Pathfinder mission, which landed on July 4, 1997. The name of the mission was appropriate for a couple of reasons.…

THE FIRST STARS MUST HAVE been a magnificent sight. Far brighter, hotter and more massive than most stars that currently light the sky, they emerged after a period of relative darkness — about 100 million years after the Big Bang, aided by the gravitation of countless halos of dark matter. No large galaxies existed yet, nor did elements heavier than helium, save for a trace of lithium. But when the first stars ended their lives as immense supernova explosions a few million years later, they released heavier elements that helped form the next generation of stars. These heavy elements, such as carbon, calcium and iron, astronomers collectively call metals. Metals helped radiate away heat from collapsing clouds of hydrogen and helium gas, fostering the creation of less-massive and longer-lived stars.…

IN THE HIERARCHY OF THE SKY, Jupiter has always enjoyed a front-row seat. With its prominence exceeded only by the Moon, Venus and occasionally Mars, Jupiter is usually the third brightest object in the night sky. It’s little wonder that the Romans named it the king of the gods. On January 7, 1610, Jupiter’s eminence surged when Galileo Galilei aimed his newly built telescope at it and observed what at first appeared to be three nearby stars hugging the regal planet. Then, on January 11, he saw four. Documenting the first planetary moons other than our own, Galileo vaulted to lasting fame. The discovery of these four worlds was one of the most momentous turning points in astronomical history, challenging the established belief that Earth was the centre of creation…

IMAGINE A CLOSE-UP VIEW OF GALAXY M87’S central regions, with its raging accretion disk distorted by the extreme gravity of the 6.5-billion-solar-mass black hole within. Now envision two tightly collimated, relativistic jets screaming out for thousands of light-years in opposite directions, perpendicular to the accretion disk. Visually detecting any trace of the blazing jet would be an extraordinary observation from 54 million light-years away, yet incredibly it’s quite possible for an observer with the proper equipment and observing conditions to succeed. M87 and its jet M87, a supergiant elliptical galaxy (classified as type-cD in the Yerkes system), is located deep in the heart of the Virgo Galaxy Cluster. M87 weighs in at around 200 times the mass of the Milky Way Galaxy. More impressively, its supermassive black hole was the…

In our May issue, we took a look at two ‘dark horse’ comets that showed some promise for amateur astronomers. Unfortunately one of them fell at the starter gate, although the second appears to be developing well. The one that failed to live up to our hopes was C/2019 Y4 (ATLAS). Following a strong surge in intrinsic brightness, a steady fading set in as the central condensation elongated and finally resolved into a line of secondary nuclei. By the latter days of April, there were enough accurate positional measurements of four of these nuclei for their individual orbits to be calculated. It being theoretically possible that each of these fragments could return in the future as separate members of a comet group — although that is very unlikely in this…

I admit it: I’m a globular cluster junkie. Before I got into amateur astronomy I’d never heard of these beautiful spherical arrays containing tens to hundreds of thousands of ancient suns. Now, nothing quite matches the real-time visual experience of a fully resolved globular. But therein lies the rub. Of the approximately 150 globular clusters in our Milky Way galaxy, relatively few resolve into myriad stars through standard backyard telescopes. The problem is not just one of distance, although the distances to most of these clusters are enormous. The bigger problem is interstellar dust. William Herschel thought “the holes in the heavens” represented an absence of stars. American astronomer E.E. Barnard, even with his decades of photographing these “vacuities,” was slow to embrace the concept that interstellar matter exists and…

NASA has announced that its next Mars rover mission now has a formal name: Perseverance. The final selection comes after a contest launched in 2019 that saw school students across the US submit 28,000 essays supporting their choice of name. Nearly 4,700 volunteers judged the essays and then winnowed the field down to 155 semi-finalists, which included the names Tenacity, Endurance and Ingenuity. NASA sought public opinion on the final choice via an online poll. Mars Perseverance is set to launch on an Atlas V rocket from Cape Canaveral Air Force Station in Florida on July 17, with a launch window running through to August 5. The rover will take about seven months to transit to the Red Planet, landing at Jezero Crater on February 18, 2021. Jezero was selected…

ONE OF THE FIRST ITEMS to check on one’s list of preparations for imaging emission nebulae is the phase of the Moon. Bright moonlight typically washes out all but the brightest emission nebulae, so most imagers simply wait for moonless nights to shoot these colourful objects. The typical exception to this rule is to image them using monochrome cameras and special narrowband filters that isolate specific regions of the visible spectrum where these ionised gasses emit light. Narrowband filters also block most moonlight as well as many sources of light pollution, so amateurs equipped with these setups could shoot pretty much any clear night. But astrophotographers with one-shot colour (OSC) cameras were left to wait for the Moon to leave the scene. That is, until recently. The new L-eNhance filter…

The COVID-19 crisis has hit the whole world hard, with awful devastation to lives, livelihoods and socialisation. The latter involves events of all kinds, including star parties and astrofests. Many have had to be cancelled or postponed during the early months of the crisis, but there are still some that are far enough away into future to be at least provisionally okay. One example is the Queensland Astrofest (qldastrofest.org.au), which at the time of writing was still a goer, although the organisers are clearly keeping a close eye on things. Even though it’s hard for everyone to get together at the moment, there are still plenty of activities in which you can get involved, both solitary and as part of larger efforts. For instance, on June 21 (the solstice), an…

I JUST WANT TO MAKE THAT CLEAR from the start: I didn’t discover Planet 9, that hypothetical, super-Earth-size world posited to lie in the outer realms of our Solar System. In fact, I didn’t discover anything. But for one day I couldn’t help but wonder: Could it be? I live in suburbia, where third-magnitude skies are a good night. But with just a moderate-size scope (23.5-cm SCT) and a good CCD camera, I can reach really faint objects that I could never have hoped for when I was limited to visual observing. Pluto, for example, is easy to catch at magnitude 14 with an exposure of a few seconds. If I increase the exposure to around 5 minutes, I can capture between magnitude 18 and 19 in good weather. I’ve…