Sky & Telescope - July 2023

www.skyandtelescope.com.au 51 M75 29 July 3 7 11 15 19 23 27 31 Aug 4 8 12 16 20 24 28 Sept 1 5 9 13 17 2125 29 Oct 3 7 11 15 19 23 31 27 Nov 4 12 8 16 20 24 28 Dec 2 6 10 14 Path of Pluto SAGITTARIUS SAO 188829 SAO 188863 SAO 188878 NUS SAO 188869 SAO 188850 SAO 188781 20h 00m 20h 01m 20h 02m 20h 03m 20h 04m 20h 05m 20h 06m 20h 07m 20h 08m –22° –23° –22° 30’ 19h 59m –23° 30’ picture Pluto’s cryovolcanoes, massive nitrogen-ice flows, towering mountains of granite-hard water ice, and methaneice ‘sand’ shaped into dune fields by the little world’s surprisingly windy atmosphere. Perhaps most remarkably, Pluto may harbour a subsurface ocean of water kept liquid by the warmth of the decay of radiogenic elements deep beneath the planet’s crust. Wouldn’t it be extraordinary if life somehow found a foothold there? To cap off our brief visit to this alien world, there’s an easy way to picture what it might be like to stand on its surface at high noon. At Pluto the Sun shines at magnitude −19.0, more than 1,200 times fainter that it does at Earth (−26.7). That’s about the same level of illumination we experience 8 to 10 minutes before sunrise and after sunset — light enough to easily find your way around, and maybe even sandboard down a methane dune. ■ BOB KING loves tracking down Pluto’s dim, distant disk.

52 AUSTRALIAN SKY & TELESCOPE July 2023 EXPLORING THE SOLAR SYSTEM by Thomas A. Dobbins and William Sheehan We’re overdue for a recurrence of one of the ringed planet’s most arresting spectacles. Known as ‘Great White Spots’ by analogy to Jupiter’s iconic Great Red Spot, Saturn’s colossal storms appear suddenly at intervals of about three decades and can expand to encircle the entire planet. If it were shorn of its magnificent rings, Saturn would appear as a paler version of Jupiter. While Saturn’s dusky belts and bright zones resemble Jupiter’s richly detailed cloudscape, they are comparatively muted in contrast and less sharply defined. The blandness of features on the planet is largely attributed to its lower temperatures, arising from its greater distance from the Sun. As a result, Saturnian clouds form deeper in its atmosphere. Saturn’s weaker gravity greatly reinforces this thermal effect. Although the planet is just 15% smaller in diameter than Jupiter, it’s only 30% as massive. The Jovian atmosphere is pulled much more powerfully toward the planet’s centre, so the pressure gradient is almost three times steeper than in Saturn’s atmosphere. Nevertheless, the ringed planet’s distended atmosphere is similar in both structure and composition to Jupiter’s, with a deck of water clouds at the bottom, a layer of ammonium hydrosulfide clouds in the middle, and clouds of frozen ammonia tinted by traces of sulfur and phosphorous compounds at the top. Above the ammonia clouds, Saturn’s upper troposphere and stratosphere contain a murky haze of photochemical smog that washes out details and subdues colors. These overlying aerosols obscure very dynamic meteorological activity. Saturn may appear quiescent compared to Jupiter, but its wind speeds are up to four times higher and its jet streams are much broader as well. Vertical convection in Saturn’s atmosphere is also far more pronounced than within Jupiter thanks to the lower gravity and greater buoyancy. These factors play a key role in generating the massive atmospheric upwellings of its Great White Spots. Throughout observational history, Suspense at Saturn Will observers be treated to an atmospheric display this apparition? 1990 EQUATORIAL STORM: NASA / JPL / STSCI; SERIES OF SIX SATURNS: NASA / JPL-CALTECH / SPACE SCIENCE INSTITUTE we’ve witnessed just six of these spots, occurring in 1876, 1903, 1933, 1960, 1990 and 2010. The 1903, 1960 and 2010 Great White Spots appeared at northern latitudes of 36°, 58° and 38°, respectively. The far more spectacular events of 1876, 1933 and 1990 formed in Saturn’s Equatorial Zone. This pattern suggests a cycle of roughly 30 years for outbreaks occurring alternately in the Equatorial Zone and at higher temperate latitudes, though the seemingly premature 2010 event broke the pattern. Curiously, each of the Equatorial Zone outbreaks first appeared at a hotspot located at a longitude extending from 290° to 315°. This calls to mind the vents that serve as the sources of Jupiter’s South Equatorial Belt revivals. All of these Great White Spots occurred during summer in Saturn’s northern hemisphere, strongly suggesting a seasonal correlation. Although heating by the distant Sun is rather feeble compared to the planet’s internal store of heat, the effect of its 27° axial tilt is greatly augmented by TThis series of images recorded by NASA’s Cassini orbiter shows the evolution of the 2010 Great White Spot over an 8-month period. SThe intense 1990 equatorial storm imaged by the Hubble Space Telescope on November 9 of that year. Dec 5, 2010 Jan 2, 2011 Feb 25, 2011

www.skyandtelescope.com.au 53 SKETCH: WILL HAY, COURTESY OF THE ROYAL ASTRONOMICAL SOCIETY / MARTIN MOBBERLEY the shadow cast by the rings, which blocks sunlight from reaching the tropical and temperate latitudes for long periods of time. Saturn ponderously circles the Sun once every 29.4 years, so each season lasts more than seven Earth years. The first indication of a Great White Spot is the appearance of a tiny, brilliant ‘pearl’. This is typically followed by multiple, closely spaced eruptive nuclei, which are violent convective upwellings reminiscent of the cumulonimbus towers of terrestrial thunderstorms. When instruments aboard NASA’s Cassini spacecraft monitored the 2010 storm from Saturnian orbit, they detected intense radio static emitted by lightning generated in its fierce turbulence. The warm plume cools as it expands, causing billowing clouds of white ammonia crystals to freeze out high above the main cloud canopy. The visible wake of the intense storm expands very rapidly in an eastward direction from its trailing end and within only a week can extend to a length of more than 100,000 kilometres to become one of the most striking planetary phenomena visible through amateur telescopes. The equatorial Great White Spots were visible even through apertures as small as 75mm. As they continue to expand, the clouds slowly lose contrast with their surroundings. Zonal winds shear them into increasingly dissipated streaks that eventually blend into the surrounding zones. Although expansion in latitude is much less pronounced, these storms can displace or even obliterate adjoining belts. Activity usually subsides after several months, although outbreaks in the Equatorial Zone persisted for four years following the Great White Spot of 1990. In 2015, Caltech planetary scientist Andrew Ingersoll proposed a detailed mechanism for the seasonal genesis of the Great White Spots. He suggested that when Saturn’s upper atmosphere undergoes seasonal cooling, it initially becomes less dense as water vapour condenses and rains out. After achieving a density minimum, there is a reversal as the remaining desiccated air (composed almost entirely of hydrogen and helium, the lightest of all gases) continues to cool. Convection is suppressed when the density of the upper atmosphere is low but resumes when its density increases sufficiently. It’s this interaction of descending cold, dry air with rising warm, moist air that triggers titanic storms. The decadeslong lag before the onset of storms arises from the very slow rate at which Saturn’s massive atmosphere radiates heat into space. Comparable planet-encircling storms don’t occur on Jupiter because Jupiter’s axial tilt is only 3°, so seasonal effects are practically nonexistent. In addition, Jupiter’s upper atmosphere is drier than Saturn’s, which is replenished by the water supplied by a steady rain of ice particles from the ring system. A lesser though still significant source of water comes from geysers on the icy moon Enceladus. No other satellite in the Solar System is known to influence the chemical composition of its parent planet. Summer solstice in Saturn’s northern hemisphere occurred in May 2017, and the autumnal equinox is coming up in May 2025. It’s high summer right now in Saturn’s northern hemisphere, and it’s been over three decades since a Great White Spot appeared in the planet’s Equatorial Zone. Observers should monitor this region closely during the current Saturn observing season. If you need any encouragement, bear in mind that of the six Great White Spots we have witnessed, four were first detected by vigilant amateur astronomers. „ Despite anticipating storms on Saturn, TOM DOBBINS and BILL SHEEHAN don’t consider themselves meteorologists. SBritish comedian and amateur astronomer Will Hay discovered a Great White Spot outbreak using his 150mm Cooke refractor on August 3, 1933. Apr 22, 2011 May 18, 2011 Aug 12, 2011

54 AUSTRALIAN SKY & TELESCOPE July 2023 W FIND YOUR WAY The finder charts peppered throughout the article will guide you to the globular clusters discussed here. THOMAS LELU WHILE OUR UNDERSTANDING of the origin of the Milky Way’s globular clusters is still shrouded in mystery, that’s not the case with their knowing distances from Earth. In fact, thanks to the most recent data from the European Space Agency’s Gaia spacecraft, we know how far away they are to within an accuracy of a few percent. The data reveal that roughly three-quarters of all known globulars in our galaxy are less than 50,000 light-years from us. In our last issue, Contributing Editor Ted Forte took readers on an extensive tour of these ‘star cities’ (AS&T: May/Jun 2023, p. 56). He visited a bunch globular clusters, with the most distant being about 50,000 light-years away. This month’s tour is going to be different since the nearest ones we’ll chase down all lie farther out! So grab your telescope — but don’t forget your binoculars as these dozen distant denizens are brighter than you think. Up, up and away! Our first target, NGC 2419 in Lynx, is an absolute must-see at the right time of the year. By carefully star-hopping 7° due north of Castor, with averted vision it’s just visible through my 8×56 binoculars as a tiny, dim smudge immediately east of 7.2-magnitude HD 60771. The view doesn’t improve much even through my 15×70s. Through my 13cm (5.1-inch) reflector at 72×, the cluster’s broad central glow and hints of a far-reaching outer halo resemble an elliptical galaxy. At 300× through my 40cm (16-inch) f/4.5 Dobsonian, NGC 2419 has a smooth, uniform appearance, but with a slightly brighter core. Harlow Shapley drew attention to this Lynx globular in 1922 after inspecting images taken with the 1m (40-inch) reflector at Lowell Observatory (among others). He not only established NGC 2419’s globular nature, but he also determined it to be one of the most remote known at the time. Thirteen years later, Walter Baade Which ‘glob’ is the farthest one you can see? 2419 α θ τ Castor LYNX GEMINI AUR +40° +30° 7h 00m 7h 30m +35° Star magnitudes2 3 4 5 6 7 Far-out Globular Clusters REMOTE GLOBULARS by Scott Harrington DOUBLE GLOBULAR M53 (right) and NGC 5053 (left) not only lie close to each other in the sky, but they may actually constitute a true binary system. You’ll find them gracing the constellation Coma Berenices.

www.skyandtelescope.com.au 55 NGC 2419 SKETCH: DAVID GRAY; NGC 5634: KATHY WALKER studied the cluster further and — based on its great distance — noted that it was possibly “an independent intergalactic object”. Today, we know that it’s nearly 290,000 light-years away — almost twice as far as the Large Magellanic Cloud (albeit lying in the opposite direction) — and is among the most luminous and massive globulars in the Milky Way. In fact, several recent studies have indicated that our ‘Intergalactic Wanderer’ may indeed have an extragalactic origin! Knots in Her Majesty’s hair The next three clusters in our tour seem out of place in the galaxy-rich constellation of Coma Berenices. The first and arguably most difficult to hunt down is NGC 4147, which you’ll find 6.4° northeast of 2nd-magnitude Beta (β) Leonis, or 3.6° west of the 9th-magnitude galaxy M85. The cluster is just visible through my 7×35s as an extremely faint ‘star’ 14′ west-southwest of 8.0-magnitude HD 105865 (not labelled in the chart below right but visible on the outer edge of the globular cluster symbol). With my 12×60s and even more so through my 15×70s, the cluster looks like a faint star with a soft, very faint halo around it. At 59× through my 13cm, HD 105865 has a yellow hue, and NGC 4147 strongly resembles a small elliptical galaxy about 2′ across with a bright core. Through my 25cm (10- inch) Schmidt-Cassegrain telescope at 117×, I see a small but bright core in a larger, diffuse halo and a faint star almost due south in the outer halo. At 260×, the small, dense core sports an irregular appearance, and there’s a star visible in the halo to the northwest. My favourite view came at 300× and above through my 40cm when the globular broke apart into a good handful of foreground and member stars scattered around a small, chunky center. Just shy of a degree northeast of 4.3-magnitude Alpha (α) Comae resides M53, the second-brightest deep-sky object in Coma Berenices. In his 1998 book Deep-Sky Companions: The Messier Objects, Stephen James O’Meara writes about M53: “… I could not positively identify it with the naked eye. I do believe someone with eyes younger than mine could.” Well, after midnight on a crisp night in March of last year, I challenged myself and came awfully close to doing so as the zodiacal band stretched faintly from Virgo to Cancer. Through my 8×56s a pair of 9.3- and 9.9-magnitude stars twinkle off the south-southeastern edge of the cluster, while through my 12×60s it spans an impressive 8′ across. During moments of steady seeing, member stars emerge at the cluster’s edges through my 25cm at 94×. Switching to a similar magnification through my 40cm, the view is stunning. The core of the cluster exhibits a square shape except for the northwestern side, which has stars exploding out of it. At 300×, it’s hard to believe that this cluster is as far away as NGC 4147, considering its boxy core alone is as broad as the entirety of NGC 4147! While there is a high probability that M53 was formed long ago in another galaxy, figuring out more than that has S INTERGALACTIC WANDERER Astronomers of the 1920s were the first to note that NGC 2419 lies at a great distance from Earth. Seventhmagnitude HD 60771 lies directly west of the globular, and an 8thmagnitude star lies just a tad beyond that. S BLINDING LIGHT The orange-yellow, 8th-magnitude star HD 127119 makes what would be an easy-to-see globular through binoculars quite difficult. The 6th-magnitude star 104 Virginis is just outside the righthand side of the frame, around 0.5° west-southwest of NGC 5634. M85 M87 M91 M98 M100 4147 5053 M53 α β ε COM VIRGO LEO M90 12h 00m 12h 30m 13h 00m +15° +20° +10° Star magnitudes2 3 4 5 6 7 8

56 AUSTRALIAN SKY & TELESCOPE July 2023 REMOTE GLOBULARS SCOTT HARRINGTON proven very difficult. Nonetheless, it does seem to have a travelling companion less than 1° away and closer than 5,000 light-years away from it in space. William Herschel swept up NGC 5053 for the first time on March 14, 1784, immediately after observing M53 with his 6m (20-foot) 47.5cm (18.7-inch mirror) reflector. Through my 8×56s, with care and patience I’m able to detect the cluster’s very faint but noticeably nonstellar glow 6′ west-northwest of a 9.7-magnitude star. Using an eyepiece yielding a 1.4° true field at 59× on my 13cm, I’m able to just squeeze both globulars into the view. Placing NGC 5053 at the centre, I note a subtle east-to-west elongation that’s even more evident through my 25cm at 94×, along with a scattering of faint stars across its surface. With almost no central brightening visible, though, it strongly resembles a low-surface-brightness dwarf galaxy! Through my 40cm at 150×, the cluster no longer looks out of round and instead is a fine mist with more than half a dozen similarmagnitude stars scattered across its face. New season on the horizon Every time I chase down NGC 5634 in the eastern reaches of Virgo, I know a new observing season is fast approaching because Antares is twinkling away in the southeast. If you can see the two 4th-magnitude stars Iota (ι) and Mu (μ) Virginis naked-eye, then you can quickly find the globular by aiming your binoculars midway between them. Through my 8×56s, I can just detect its ghostly presence immediately northwest of 8.0-magnitude HD 127119, while my 12×60s show, with averted vision, a soft glow jutting out from the star’s glare. The view is so tantalising that it demands a look through a scope. Indeed, at 59× through my 13cm the cluster appears 1.5′ wide with a bright, broad core and an 11.9-magnitude star sitting 1.7′ to its northwest. NGC 5634 displays no central brightening even at 260× through my 25cm, but I do see flashes of a few stars scattered over its surface at 400×. Only in the previous two decades have we gleaned that NGC 5634 is likely an orphan from another galaxy. Scientists attribute the cluster’s origin to a dwarf galaxy dubbed Gaia-Enceladus, one of several remnants of a past galactic merger with the Milky Way, the earliest and most massive known to date. Down and out Lurking nearly 7.5° east of 3.3-magnitude Pi (π) Hydrae, near the tip of the Water Snake’s tail, is NGC 5694 — the third most distant globular on our tour. When the 3.5°-long, wavelike star chain formed by 4 Librae and 54, 55, 56, 57 and 58 Hydrae appears in the binocular field, I know to look just right of it to find the cluster. While doable through my 8×56s, NGC 5694 is easier to see through my 12×60s as a 10th-magnitude dot nearly 12′ north of 7.0-magnitude HD 128787. At 27× through my 13cm, I see a very small glow with what looks like a faint star at its centre. Only at 200× through my 40cm does the cluster start to look grainy, and at 300× it grows gradually brighter, from halo to core to a faint stellar point. However, the view that absolutely took my breath away one crisp morning was when I swept it up through my 40cm with a newly acquired 20mm eyepiece boasting a 100° apparent field of view. Yielding a true field of 1.1° at 91×, NGC 5694 appeared as a dynamic glow just shy of 1′ across that seemed to float at the northern end of a chain of brighter stars. Next is NGC 5824, in northwestern Lupus, less than 20′ from the border with Centaurus. Scottish astronomer James Dunlop discovered it in 1826 5634 5694 5824 S 54 104 55 56 57 58 4 D1 D2 V N P L LIBRA VIRGO CEN HYDRA LUPUS 14h 30m –10° 14h 00m 15h 00m –20° –30° HD 132955 Star magnitudes2 3 4 5 6 7 M14 47 IC 1257 β γ σ OPHIUCHUS 6426 +5° –5° 0° 17h 40m 17h 20 Star magnitudes m 2 3 4 5 6 7 8 T MANY VIEWS A variety of optics will provide delightful views of NGC 5694. Besides the arc of stars to its east, you can also orientate yourself with 7th-magnitude HD 128787, which lies south of the cluster, immediately outside the frame of the sketch (it’s the orange speck in the chart at right, just right of the label 56).

www.skyandtelescope.com.au 57 NGC 6426: RUDOLF RIEDL while he was working in Australia. To find the globular, drop about 7.4° down from 3rd-magnitude Sigma (σ) Librae to 5th-magnitude HD 132955, and from there go another 0.5° south-southeast. While not the brightest globular in Lupus, NGC 5824 does hold the distinction of being the farthest one I’ve seen through my 7×35s — it’s at an incredible distance of 103,400 light-years. With scrutiny, the globular is vaguely nonstellar through my 12×60s, while 27× through my 13cm reveals a faint star to its north. At 117× through my 25cm, NGC 5824 spans just 1′ and displays a compact core set in a distinct halo, which reminds me of NGC 4147. The 17th hour Our next two globulars lie on the eastern flank of the expansive constellation Ophiuchus and offer quite a visual contrast. The first one, IC 1257, at magnitude 13.8 is the faintest object on our tour and the only one not visible through my binoculars. It’s just 2° south of the 4.5-magnitude star 47 Ophiuchi, and with my 13cm at 59× I see an extremely faint, nonstellar smudge almost exactly midway between a 12′-wide pair of 11th-magnitude stars. While the cluster’s entire glow spans less than 1′ through my 40cm, at 150× I’m still able to make out a nearly stellar core surrounded by a very faint halo. Even with 664× in a 91m (36-inch) alt-az-driven Dobsonian, I only noted a soft glow with a slightly brighter center and hints of irregular chunkiness all over. IC 1257 is dimmed by more than two full magnitudes due to its location behind the galactic bulge on the far side of the Milky Way’s disk. American astronomer Edward Emerson Barnard and Austrian astronomer Rudolf Spitaler, on either side of the Atlantic, spotted it one night apart in 1890, thanks to a faint comet passing nearby. However, its early (mis)classification as an open cluster wasn’t fully questioned until the 1990s when the late Czernic Crute (Los Angeles Astronomical Society) brought the problematic nature of IC 1257 to the attention of Brian Skiff (Lowell Observatory) — ever a friend to amateur astronomers. Skiff, in turn, alerted his colleagues in amateur and professional circles, including William Harris, a renowned globular cluster researcher. Shortly thereafter, the 5m (200-inch) Hale reflector at Palomar Observatory captured images of it, confirming it to be a “moderately low-luminosity halo cluster”. NGC 6426 is easier to find — look for it about 1.5° southsoutheast of 3rd-magnitude Beta Ophiuchi or 0.9° northwest of 4th-magnitude Gamma (γ) Ophiuchi. However, the smallest binoculars I have that show it are my 12×60s, which reveal the cluster as a very faint patch a few arcseconds across. At 94× through my 25cm, it’s a delicate glow gently elongated east to west, with even surface brightness throughout. At 200× through the 25cm, the globular reminds me of the open cluster M46 in Puppis through my 8×56s! Only through my 40cm at 300× does the cluster’s uniformity break S EYEPIECE SURPRISE While the author can’t make out NGC 6426 through his 8×56s, he was surprised to find that he could just split the 21″-wide double star 61 Ophiuchi, which lies only 36′ south. Fourthmagnitude Gamma Ophiuchi is the bright star at left. down and I’m able to detect a small central brightening. I see no resolution or granularity, however, except for three stars equally spaced along the western edge. Can you spy any member stars? The forgotten labour If you ever travel far enough north to observe it, little NGC 6229 is a worthy binocular challenge 4.8° east-northeast of 4th-magnitude Tau (τ) Herculis in the northern reaches of the constellation. Under dark skies, my 7×35s reveal it to be the faintest ‘star’ in a near-equilateral triangle with two 8th-magnitude suns immediately west of it. The cluster has a peculiar softness to it through my 12×60s and looks like a bloated star through my 15×70s. If only Herschel (who discovered it) could have known that his class IV (of planetary nebulae) find was a tightly packed cluster of stars nearly 100,000 light-years distant! Even through my 13cm at 27×, it’s hard for me not to pass right over it due to its compactness. A broad core of high surface brightness with very little outer halo is all that my 25cm at 200× reveals. It’s so compressed that I can see why Herschel erred in his classification. At 400× the

58 AUSTRALIAN SKY & TELESCOPE July 2023 REMOTE GLOBULARS NGC 6229: VITALI PELENJOW; NGC 7006: STEFAN BINNEWIES / FRANK SACKENHEIM / JOSEF PÖPSEL / CAPELLA OBSERVATORY cluster’s glow is 1.6′ across, and there’s a slight mottling to the core and halo. Fascinatingly, NGC 6229 as well as IC 1257, NGC 5634, and NGC 4147 all seem to have their origin in Gaia-Enceladus. If you read Steve Gottlieb’s article on the Sagittarius Dwarf Spheroidal Galaxy (AS&T: Nov/Dec 2021, p. 56), then you know that M54 is special in many ways. But one thing he didn’t tell you is its potential to be the farthest object in our galaxy visible to the naked-eye — it’s about 86,000 light-years away and yet shines at magnitude 7.5. In fact, it wouldn’t be such a challenge if its light weren’t subject to half a magnitude of interstellar dimming. Through my 8×56s, M54 looks like a soft, 8th-magnitude star, while through my 13cm at 59× it has a stellar core. I can see a faint foreground star lodged in the southeastern part of its outer halo through my 25cm at 200×. Only with 336× in the 91cm Dob can I start to see resolution in the outer third of the cluster. Winter’s end Our final target is an incredible sight considering its light is visible through my 8×56s and yet has been skimming along the southern side of the Milky Way’s disk for about 130,000 years before reaching us. To find NGC 7006, start at 4th-magnitude Gamma Delphini — a tight pair of bright, golden suns at 27× through my 13cm. The globular lies about S NORTHERLY BEACON At magnitude 9.3, NGC 6229 is the 13th brightest globular cluster in the Northern Celestial Hemisphere. A pair of 8th-magnitude stars guard the globular on its right. T DAINTY IN THE DOLPHIN To globular cluster aficionados, NGC 7006 is only the first of three globulars discovered in the celestial Dolphin. Seventh-magnitude HD 200393 (the reddish star in the image) points the way: Look for the globular a smidgen more than 20′ northwest of the star.

www.skyandtelescope.com.au 59 M92 6229 E I V W HERCULES 17 DRACO h 00m 16h 30m +50° +45° +40° Star magnitudes 8 7 6 5 4 3 2 M15 7006 α β δ δ ε γ γ DELPHINUS EQU 21h 30m 21h 00m +20° +15° +10° Star magnitudes 7 6 5 4 3 2 M22 M28 M54 M69 M70 δ ε φ γ λ σ τ ζ SAGITTARIUS –35° 19h 00m –25° 18h 30m –30° Star magnitudes 7 6 5 4 3 2 3.5° due east, but I’ve found it’s easy to overshoot it and land on the Toadstool instead, a possible open cluster that amateur and author Phil Harrington discovered in 1993 and was so nicknamed by former AS&T Contributing Editor Sue French. Once acquired, NGC 7006 is a small but distinctly nonstellar glow whose size and tiny core are reminiscent of a little galaxy. At 105× through my 40cm, its entirety spans just 1.5′ and reminds me of what NGC 6229 looked like at 59× through my 13cm. Increasing to 300×, I see a broad core that brightens just a bit at the centre, along with a distinct stellar pair just 1.5′ south and a couple of fainter stars northeast of the cluster. By starting with NGC 2419 ‘above’ (north of) the Milky Way’s disk and finishing just ‘below’ it with NGC 7006, we travelled more than 120° across the sky. In so doing, we took advantage of the fact that the majority of globulars beyond Distant denizens Object Constellation Mag(v) B * Mag(v) Distance (kl-y) Size RA Dec. NGC 2419 Lynx 10.6 17.3 288.6 4.6′ 07h 38.1m +38° 53′ NGC 4147 Coma Berenices 10.3 14.5 60.5 4.4′ 12h 10.1m +18° 33′ M53 Coma Berenices 7.7 13.8 60.3 13′ 13h 12.9m +18° 10′ NGC 5053 Coma Berenices 9.9 13.8 57.2 10′ 13h 16.5m +17° 42′ NGC 5634 Virgo 9.5 15.5 84.7 5.5′ 14h 29.6m –05° 59′ NGC 5694 Hydra 9.9 15.5 113.6 4.3′ 14h 39.6m –26° 32′ NGC 5824 Lupus 8.9 15.5 103.4 7.4′ 15h 04.0m –33° 04′ IC 1257 Ophiuchus 13.8 17.5 86.7 5.0′ 17h 27.1m –07° 06′ NGC 6426 Ophiuchus 11.1 15.2 67.5 4.2′ 17h 44.9m +03° 10′ NGC 6229 Hercules 9.3 15.5 98.2 4.5′ 16h 47.0m +47° 32′ M54 Sagittarius 7.6 15.2 85.7 12′ 18h 55.1m –30° 29′ NGC 7006 Delphinus 10.7 15.6 128.2 3.6′ 21h 01.5m +16° 11′ Angular sizes are from recent catalogues. Visually, an object’s size is often smaller than the catalogued value and varies according to the aperture and magnification of the viewing instrument. Right ascension and declination are for equinox 2000.0. B * Mag(v) is the estimated brightness of the brightest stars — your telescope must reach this magnitude to partially resolve the cluster. 50,000 light-years from the centre of our galaxy all currently reside north of its disk. That, coupled with the possibility that many of the outer halo globular clusters were captured during mergers, makes me savour each view just that much more. I hope you will, too. „ With nothing more than 8×56s, SCOTT HARRINGTON has seen about half of the Milky Way’s globular clusters — and would love to help you do the same! You can reach him at [email protected]. FURTHER READING: Check out Bill Tschumy’s free app, Our Galaxy 2.0, which you can use to better explore the locations of each globular discussed (otherwise.com). Among other globular cluster resources, you’ll find a database maintained by William Harris at https://is.gd/harris_globulars.

60 AUSTRALIAN SKY & TELESCOPE July 2023 IMAGE PROCESSING by Ron Brecher ALL IMAGES COURTESY OF AUTHOR Deep sky astrophotography is a hobby that requires mastering several skillsets. The mechanical knowhow needed to record good deep sky data doesn’t necessarily overlap with the skills required to turn all those data into beautiful images. In fact, these days, you don’t even need to acquire your own image data — you can buy time on a finely tuned telescope located under dark skies. You can even work with images acquired by NASA observatories like the James Webb Space Telescope. But regardless of where and how our photons are gathered, it takes powerful image-processing software — and an understanding of how to use it — to turn those ones and zeroes into dazzling portraits of nebulae, star clusters, galaxies and the occasional bright comet. I have some good news and some bad news. The bad news is there is no ‘Astronomy Picture of the Day’ button in any software I’ve seen — you really have to work the image data carefully to produce a nice result. The good news is that it doesn’t take many steps to get there. And while there is a host of software you can use, among the most popular for amateurs today is PixInsight, or PI (pixinsight. com). This program operates on any platform and is written by astrophotographers for astrophotographers. It uses a modular, open-architecture system that encourages users to develop their own add-ons and scripts, which in turn fosters the growth of a large online community to share these improvements. PI can cover almost any task you’ll likely encounter in astronomical image processing. And while it was developed with a focus on deep sky imaging, it has many tools to improve lunar, solar and planetary images. Here are some basic processing steps that I use that will illustrate the program’s utility. Master the basics of the most popular astronomical image-processing software. Priming for PixInsight PI CAN DO IT ALL PixInsight is a versatile astronomical image-processing workhorse suitable for deep sky imagery as well as nightscapes and even planetary photography. While it has hundreds of processes and scripts, only a handful were needed to produce this deep, colourful photo of M31 in Andromeda.

www.skyandtelescope.com.au 61 The main controls Knowing your way around the PI workspace is essential to getting the most from the software, so it’s worth spending some time learning its user interface before you start working on your pictures in earnest. There’s a free, 5-part video series to help show you the ropes at https://is.gd/PIprimer. However, if you just want to get straight to using the program’s tools, you’ll find them grouped in subfolders within the PROCESS pulldown menu located at the top of the screen. You can also display an alphabetical list of all the processes by selecting PROCESS > All Processes. Users can combine several of these into another type of command called scripts that are listed within the SCRIPT menu, which is also subdivided into several groups. A script executes a sequence of tasks, automates complex operations, or otherwise extends PI’s capabilities. You’ll also find some useful tabs along the left side of the workspace. The Process Console reports the progress of any actions being executed and lists warnings or errors if encountered. The History Explorer stores and displays everything done to an image and allows you to quickly go back to a previous state if needed. Double-clicking a process name in the History Explorer opens that process with the settings that were used. Data reduction The first step in converting a set of raw data into a finished photo — an exercise known as data reduction — uses the WeightedBatchPreprocessing (WBPP) script. WBPP is a little like the conductor in an orchestra made up of various PI processes, telling each one what to do and when to do it. For example, the script creates one master image per colour filter from all the individual sub-exposures and calibration frames. It then completes all the data-reduction steps for your light exposures, including calibration and alignment before stacking them into a single image ready to be worked up into a pretty picture. The WBPP script examines each image and ranks it by quality to use the most data from the best subframes, with less contribution coming from the lowerquality images included in the stack. The subframe image quality is evaluated by measuring each image’s signal-tonoise ratio as well as the full-width, half-maximum (FWHM) parameter that examines the size and shape of stars. To use the WBPP script, launch it and then load all your calibration and light frames using the +File or +Directory buttons at the bottom of the script window. The program will automatically put the files in the proper locations in the script window using the information recorded in each file’s FITS header. (You can inspect the FITS header of an open image using FILE > FITS Header). If your acquisition software doesn’t write this information into the FITS header, load the S CONVENIENT CALIBRATION The WeightedBatchPreprocessing script is the first step in producing an image from raw and calibration frames, orchestrating every aspect of data reduction. It includes the essentials of calibration, alignment, stacking and other advanced features. T DETAIL IN THE DARKNESS Straight out of the camera, images look almost entirely black, but there is detail hiding in the shadows. The ScreenTransferFunction process performs a screen stretch on linear images to display the detail in the dark areas without altering the underlying data.

62 AUSTRALIAN SKY & TELESCOPE July 2023 files using the Add Custom button at the bottom of the script window and input the details manually. You’ll need to verify the settings on each tab and specify an output folder. When ready, run the script; it’ll warn you of any potential issues before running. Once the master frames are all generated, you’re ready for the next step. Note that colour images may come from using a colour camera or can be made by combining red-, green- and blue-filtered monochrome images. In the latter case, you’ll need to combine the filtered shots into a colour image using the ChannelCombination process, where you’ll assign each filtered master file to its proper channel. While your camera’s files will most likely be in the FIT format (or RAW files from DSLR cameras like CR2 or NEF), PixInsight saves images as Extensible Image Serialisation Format (XISF) files by default. This format saves more information about the processes applied to the file than other types. Still, the software can open and save files as FIT, TIF, PNG, BMP, JPG and more. As with almost any unprocessed deep sky image, the raw frames or reduced masters generated by WBPP appear virtually all black, with a smattering of bright pixels marking the location of the brightest stars. This is normal — the images aren’t actually black, they’re just very, very dark because your monitor can’t display the full range of brightness present in the images. This is simply a result of the data being in a linear state, meaning that the brightness of each pixel is proportional to the number of photons that fell on it. Visualising raw data Many of the early steps in deep sky image processing are applied to linear files. To make an image that shows the wealth of detail you desire, you’ll need to selectively brighten the image while preventing the brightest pixels from becoming saturated and keeping the background dark. This stretching process results in a non-linear image that displays subtle differences in brightness and hue. Most of the final finishing in image processing is done on images after stretching. However, linear images don’t display very well, making processing decisions tricky. Enter one of PixInsight’s most helpful features, the ScreenTransferFunction (STF) found at PROCESS > IntensityTransformation > ScreenTransferFunction. STF brightens and applies contrast and colour balance to the displayed image without changing the underlying data. You can apply STF by pressing Ctrl + A (or Cmd + A on a Mac), but you’ll need the process window open to finesse its settings or to reset it. It’s important to reapply the STF tool each time you make a change to the image for it to display correctly. (When using the tool on colour images, be sure to uncheck the chain-link icon at upper left of the process window until after you’ve balanced the colour as described later.) It’s well worth reading the tool’s TX PALETTE ASSEMBLY The ChannelCombination process (below) was used to make the colour photo of M31 at far right from images taken with a monochrome camera and blue, green and red filters (seen left to right, respectively). TX NO CRUST, PLEASE It’s important to crop out non-overlapping areas along the edge that result from aligning and stacking images. You use the DynamicCrop process for this. This step also allows you to adjust the framing of the composition. IMAGE PROCESSING

www.skyandtelescope.com.au 63 accompanying documentation, available by clicking the document icon at the bottom right of the process window. The next steps in my basic linear workflow involve removing unwanted signal from my images. I start with a DynamicCrop process to eliminate any edge artifacts that could negatively affect the picure, such as non-overlapping areas due to dithering or other pointing differences when shooting my target over multiple nights. This is accomplished using PROCESS > Geometry > DynamicCrop. In the process window enter the size you want to crop to in the Size/Position section, and the angle of the crop in the Rotation section. You can also make these adjustments by manipulating the preview of the crop with the mouse. When ready, click on the Execute (green checkmark) button at the bottom left of the process window. With a nicely framed image in hand, I then perform another STF stretch to check the image for gradients — uneven field illumination, often due to moonlight or light pollution. Imperfect flat-field calibration can also add gradients to your image. Fortunately, there are two powerful processes in PI to tackle this problem. AutomaticBackgroundExtractor (ABE) works reasonably well, with little or no adjustments. When activated, you’ll need to specify the type of correction to make and whether the ABE should replace the current image or generate a new image. The more complex DynamicBackgroundExtraction (DBE) tool produces superior results compared to ABE. I highly recommend investing the time needed to master DBE, since most deep sky images will have some gradients, and DBE can remove them effectively. DBE requires you to place points (called samples) in the background regions of your image. It then builds and applies a background model. Since gradients are large-scale, just a few sample points will do. In this window, I typically increase the Tolerance to 2.0 and the Shadows Relaxation setting to 6.0 in the Model Parameters (1) section. Then I move down to the Sample Generation area and change the Default sample radius to between 50 and 100 pixels and the Samples per row to 3 or 4 in order to get a good estimate of the background. This typically produces a dozen or more sample points, which results in a good representation of the gradient I want to correct. With gradients addressed, I then move on to establishing the image’s colour TX GRADIENT SUPPRESSION Using the DynamicBackgroundExtraction process removes uneven field illumination that results in brightness gradients like the greenish brightening in the left side of the image below and corrected in the result at right.

64 AUSTRALIAN SKY & TELESCOPE July 2023 T MORE CONTRAST After you’ve stretched your picture (left), you can apply LocalHistogramEqualization to boost low-contrast regions in your image (right). It can be used in multiple passes to enhance both small- and large-scale features. T BIG STRETCH The HistogramTransformation process is where you’ll permanently stretch the image. The ScreenTransferFunction settings can be conveniently transferred to this process with the click of a mouse and then adjusted, if necessary, before being applied to your photo. T FINAL TWEAKS The CurvesTransformation tool allows you to adjust any individual colour channel’s brightness and saturation. All the picture at left needed was a saturation boost and a little increase in overall brightness (center) before it was suitable for displaying on the web (right). IMAGE PROCESSING

www.skyandtelescope.com.au 65 balance. PixInsight’s ColourCalibration process works very well on RGB or natural-colour images. To use this process, I specify the location of a background region, which is used to colour-balance the darkest pixels in the image. It then discerns the location of stars in the image and uses them as the White Reference. Here I’ll click Alt + N (Option + N on a Mac) to enter New Preview mode and define a small preview containing just background sky. I then set this preview as the Reference image in the Background Reference section and click the square at the bottom left to apply the process. After balancing the colour, be sure to invoke a STF with the chain-link icon at the left of the process window activated in order to link the colour channels. Narrowband images also require adjustment to obtain a pleasing colour palette. However, colour balance with representational colour is fairly subjective and can be approached differently. The last step before non-linear stretching is to address any unsightly noise in the image. All deep sky images contain some noise, and it tends to be most visible in the darkest regions of the picture. PixInsight includes several noisereduction tools that are fairly complex to operate, so I prefer Russ Croman’s NoiseXTerminator (NoiseXT) available at https://is.gd/NoiseXT ($59.95). This plug-in works better than any other method and is extremely easy to use. Once installed, you’ll find it under PROCESS > NoiseReduction. Non-linear processing With the linear processing steps now complete, I can apply a permanent stretch to make the image non-linear. This is done using the HistogramTransformation (HT) process in conjunction with the STF process. First open STF, click on your image, and then click Ctrl + A. Next, copy the settings by clicking and dragging the New Instance triangle at the bottom left over to the bottom bar of the HT window. You can then adjust the shadow and midtone sliders to suit your taste, and then apply to the image by clicking the square button at the bottom left of the process window. If you’d rather perform this task manually, the adjustments are made in the HT window using the sliders in the lower graph, while the predicted result of the stretch will be displayed in the top histogram. I begin by moving the midtone slider to the left until I start to see the histogram peak move away from the left side of the graph. Then, using the scroll wheel on my mouse, I’ll zoom in on the bottom graph and adjust the shadow slider. I move it to the right, where the histogram begins to rise steeply. At this point ensure the STF is turned off by hitting the Reset button at the bottom-right corner of the STF window. Next, open a RealTime Preview by clicking the open-circle icon in the bottom left of the HT window. While looking at the preview image and the histogram, I’ll adjust the midtone slider again to achieve the look I want. I then click the square Apply button at the bottom left, and in moments the result is displayed. After stretching, there are many additional enhancement options in PixInsight. Most astrophotographers make further adjustments to the brightness, contrast, hue, saturation and sharpness. These steps can turn a good image into a great one. Boosting contrast is particularly important and is performed with the LocalHistogramEqualization (LHE) process. This tool is very powerful, so it requires a light touch. The Amount slider adjusts how much contrast boost is applied. Be aware that, particularly when using a small kernel radius, LHE can generate artifacts that appear as dark rings around stars, which require masks and other more advanced techniques to prevent. I often finish up with the CurvesTransformation process, adjusting the RGB/K (which controls brightness and contrast) and Saturation (S) curves. Finally, when I’m ready to share my image with friends, it’s helpful to embed a colour profile in the JPG file. This tells web browsers and devices like printers and monitors how the colours in the image should be displayed. I use the ICCProfileTransformation process to ensure that my shared JPG images contain the sRGB colour profile that is widely used by default. In closing PixInsight is one of the most popular software packages for processing just about any kind of astronomical image. It’s extremely versatile, though it takes some time to familiarise yourself with its collection of hundreds of processes and scripts — not to mention all the additional scripts and processes developed by other users. Beginners can get good results by setting the simple goal of mastering the user interface and the tools described above. As your skills improve, you can add other processing steps, but the ones I’ve highlighted will likely always be at the centre of your workflow. „ RON BRECHER hosts PixInsight image-processing workshops at mastersofpixinsight.com. S DO YOU SEE WHAT I SEE? Before saving your image as a JPEG to share or print, make sure other devices know how it should be displayed. Use the ICCProfileTransformation process to embed the sRGB colour profile in your image that provides printers and display devices the correct colour information.

66 AUSTRALIAN SKY & TELESCOPE July 2023 AS&T TEST REPORT by Rod Mollise ALL IMAGES COURTESY OF THE AUTHOR WHEN I REVIEW a telescope, I like to look at the manufacturer’s ads to see what they think deserves mention. What’s special about the instrument? Sky-Watcher’s advertisement for the Virtuoso 150P Tabletop f/5 Dobsonian reflector leads off with “These ain’t no toys”. Which (despite the double negative) started me thinking. The past 40 years of amateur astronomy has been the age of huge telescopes — a time when a 30cm-aperture instrument is considered ‘small’ by some. When I was a young astronomer, however, the 150mm (6-inch) Newtonian reflector was the norm, and amateurs did amazing work with it. A scope of this size is both “portable and powerful,” as Sky-Watcher’s ad also states. The Virtuoso package I hadn’t used a 150mm reflector in a long time and was hopeful this one might be worth coming home to, but I was skeptical. The manufacturer makes Sky-Watcher Virtuoso GTi 150P Australian price: $799.99 skywatcheraustralia.com.au What we like Excellent optics Accurate Go To Freedom Find keeps alignment What we don’t like Helical focuser rough motion Manual doesn’t cover control app W The Virtuoso 150P is a 150mm (6-inch), f/5 Newtonian reflector on a compact Go To mount controlled with either the manufacturer’s SynScan or SynScan Pro smartphone apps. A tabletop Go To Dobsonian Sky-Watcher’s Virtuoso GTi 150P adds a computerised mount to this capable 150mm Newtonian.

www.skyandtelescope.com.au 67 W The Virtuoso 150P upper tube assembly showing the helical focuser, light baffle opposite the focuser, and secondary mirror. a lot of claims about the capabilities of this fairly inexpensive scope. In addition to featuring a collapsible tube, 94% reflectivity ‘Radiant Aluminium Quartz’ mirror coatings, and two widefield ‘Super’ eyepieces, the Virtuoso is also equipped with dual-axis drives and a Go To computer. The ad also says the telescope can find and track more than 10,000 objects when used with a free smartphone app. That’s a big claim for a 150mm scope. The Virtuoso arrived double boxed. It took a little doing to extract the scope, which was tightly held in place by its foam packing. Thankfully, the scope was easy to assemble and nearly ready to go out of the box. All you need do is mount the tube on the single-arm, alt-azimuth mount with its Vixen-style dovetail bracket, attach the finder, and extend the front section of the truss-style tube. The rear 38 centimetres is a solid (steel) tube, but the front 30.5 cm is composed of two small rods attached to a ring that holds the secondarymirror assembly, focuser, and a light shield opposite from the focuser. In its stowed position, the front portion is collapsed, making the whole tube assembly only a little over 40 cm long. When extended, the rods are locked in place with two nylon bolts. Sitting on a table, the telescope looks attractive. The shiny black steel tube, the futuristic-looking truss assembly, and the pretty blackand-white-finished mount dispelled some of my doubts — until I noticed the whole thing was tilted. One of the three plastic feet on the base was missing, broken off during shipping, no doubt, leaving a gaping hole in the particleboard base. Although the telescope was sitting on a piece of packing foam in the box, that apparently wasn’t enough to prevent shipping damage. Fortunately, the foot was easy to reattach with the aid of some glue. With the scope assembled, I had a look at the accessories. The included 25mm and 10mm eyepieces didn’t inspire much confidence. Both have metal barrels, but their upper assemblies are plastic. Also included is a unit-power red-dot finder. After some digging through the manual (which covers three different models of Virtuoso scope), I learned that the finder mounts on the tube upper assembly. I switched it on but saw no red dot — batteries not included. Luckily, I had the required CR 2032 battery on hand. The telescope’s computer and motor S The tube of the Virtuoso 150P measures 69 centimetres with the focusing ring extended and collapses to 41 cm for transport and storage. Weighing a total of 8.6 kilograms, the scope should be easy for most observers to carry around and set up. S Both the primary and secondary mirror cells are fully adjustable with three alignment screws each. The centre of the primary mirror is marked to aid collimation. S The telescope’s unit-power red-dot finder attaches to the secondary ring above one of the two trusses. The helical focuser secures eyepieces with two knurled thumbscrews.

68 AUSTRALIAN SKY & TELESCOPE July 2023 AS&T TEST REPORT are powered by 8 AA batteries. That’s convenient for occasional use but can get expensive quickly if you use the telescope often. Rechargeable cells worked for me. The best bet, though, is the DC/cigarette-lighter cable Sky-Watcher Australia sells for $19.99. One caveat is the power input port rotates with the telescope, so the adapter’s cord can get wrapped up in the mount. Before first light, I always check the alignment of the primary and secondary mirrors. The scope comes with a ‘collimation cap,’ a plastic cap with a small hole in its centre that fits in the focuser and aids optical alignment. The company also conveniently marks the centre of the primary mirror with a circular sticker. While I used my own collimation tool, I verified the cap also showed the mirrors in alignment. The instructions in the manual will enable most beginners to adjust the scope properly. Out of the box, mirror alignment was pretty close anyway. The telescope’s focuser is a helical model, a threaded tube that screws in and out to focus. I’m not a fan of the design, and this one seemed poorer than most. Its threads are coarse, and black paint on the unlubricated threads makes the action particularly rough. It’s a bit wobbly and lacks a lock screw to reduce wobble and hold focus in place. Before using the telescope, users have to download the SynScan Pro app to allow the Virtuoso to find and track objects. An optional SynScan hand control can be used with the telescope (and adds $224.99 to the price). The app, however, is free from both the Apple App Store and the Google Play Store and runs on almost any smartphone or tablet. There’s also a basic SynScan app, but it has fewer options and was slower to connect to my iPhone. However, the pro version downloaded and installed without problems. I spent some time reading the SynScan Pro app documentation I downloaded from the Sky-Watcher website at https://is.gd/synscan_app (the printed manual included with the scope says little about the app). Ideally, these instructions should be included in the main manual. Despite the document’s lack of illustrations and step-by step instructions, after reading it and exploring the help files built into the app, I was ready to go. However, I still had to decide where S The optical tube assembly attaches to the single-arm Dobsonian mount with a standard Vixen-style dovetail clamp. This enables users to balance the scope when adding heavier eyepieces and Barlows, or to swap in other OTAs, provided they clear the Virtuoso’s drive base. S The outside face of the altitude arm contains the battery compartment as well as inputs for an optional SynScan hand paddle, a DC power input and a SNAP port to control certain DSLR and mirrorless cameras (seen left to right, respectively). The Wi-Fi power indicator flashes red twice per second when the scope is on. S The Virtuoso 150P focuser stands just 76 centimetres above the ground at best, so users will need a table or some other lift to bring the scope to a comfortable viewing height. S The telescope comes with 25- and 10mm long-eye-relief ‘super’ eyepieces as well as a simple but functional collimation cap to help users align the optics.

www.skyandtelescope.com.au 69 to use the scope. Sky-Watcher calls this a ‘tabletop’ Dobsonian, and they aren’t kidding. The eyepiece is a mere 76 cm off the ground when the scope is pointed at the zenith. So, I placed the Dob on a small folding aluminium camp table. It was reasonably steady but not the Rock of Gibraltar, and the spot where I placed it on my driveway wasn’t quite level. Would these things lead to an ‘alignment failed’ message? Go To alignment I thought on the first night out I’d simply concentrate on getting the Go To working. With the Virtuoso 150P, this starts by connecting to a smart device. Some Wi-Fi enabled telescopes I’ve used have had trouble connecting and staying connected. Not this scope. I turned it on, chose ‘SynScan 5500’ in my iPhone’s Wi-Fi menu, and the app connected and stayed connected. I could walk to the other side of the backyard and still maintain connection. So far, so good. Next came aligning the system. There are four options in the app: 1-Star Alignment, Level Alignment (two stars), Brightest Star Alignment (two stars), and 3-Star Alignment. In each case, the scope initially has to be in its ‘Home Position’ with the scope pointed south and the tube level (with the help of the built-in bubble level). Typically, the scope slews to alignment stars the user chooses from a list arranged in order of magnitude. However, with the Brightest Star option, you centre the first star through the eyepiece by using the direction buttons on the app screen before the scope slews automatically to the second star to complete the alignment process. I tested each alignment method and found the three that use multiple stars comparably accurate. Often Brightest Star was handy for my suburban backyard, because the alignment list only includes the brightest stars and planets. The 1-Star routine worked best when observing objects near the selected alignment star. With the Virtuoso in Home Position, I tightened the altitude and azimuth clutches enough to hold the telescope in place but left them loose enough to move the telescope easily by hand. The app’s Freedom Find feature allows you to push the Virtuoso by hand without ruining the Go To alignment, thanks to the presence of auxiliary encoders on each axis. I chose two stars from the list in SynScan Pro and, after the scope slewed to them, centred each through the eyepiece. SynScan Pro provides nine slewing speeds to accommodate coarse and fine centring. My first selection was a star, but the second ‘star’ was actually Saturn. The Virtuoso had no trouble using planets for alignment. After centring both, the app displayed ‘alignment successful’. And it was! Every target I requested, from horizon to horizon, was visible in the field of the 25mm eyepiece (30×) when a slew stopped. This, despite my table being not quite level. Pleasant observing It was time to have some observing fun. While SynScan Pro only displays lists of potential targets — there are no star charts — it works well. My first stop was a bright but compact globular cluster. The slew ended with the object in the eyepiece field, I centred it with the direction buttons, and I inserted the 10mm eyepiece. The helical focuser wasn’t as bad as I feared; it was mostly screwed in at infinity focus and not too wobbly. I had a look and rubbed my eyes — was I seeing some resolution in this tight cluster? I ran inside, fetched a 4.7mm eyepiece for higher magnification, and had a good, long look. I was seeing not just the brilliant core, but, yes, a splash of tiny stars. Every object I visited showed more detail than I remembered a 150mm being capable of producing. M27, the Dumbbell Nebula, was was a spectacle, especially when I added a light-pollution filter to the 25mm eyepiece. The oculars turned out to be better than I expected. They both feature comfortable 65° apparent fields, good eye relief, and while edge-of-field performance isn’t great — stars ¾ away from the centre began to look like comets — I mostly concentrated on what was in the middle of the field and just enjoyed. At low power, the scope has an expansive field of view and is wellsuited for wandering around the Milky Way. Staring at another globular cluster, I was taken by the beauty of the image. This 150mm had enough lightgathering power to pull in hordes of background suns. There was one problem, though. Despite the presence of a baffle opposite The Virtuoso mount includes a SNAP port to control some DSLR and mirrorless cameras, though it wasn’t needed to take this snapshot of the Moon with an iPhone held up to the 25mm eyepiece.

70 AUSTRALIAN SKY & TELESCOPE July 2023 AS&T TEST REPORT the focuser, stray light from neighbours’ lights sometimes spoiled my views. Most big Dobsonians have cloth or plastic light ‘shrouds’ over their truss assemblies to prevent this. Some kind of shroud for the Virtuoso could be made easily and would help. On another evening, I assessed the optical quality of the telescope by viewing the planets and doing a startest. First stop was the young Moon. The contrasty images the Virtuoso produced were so luscious I couldn’t resist holding my iPhone up to the eyepiece and making a portrait of Luna. The planets Jupiter and Saturn were attractive too but demonstrate a limit of the scope’s ‘fast’ f/5 optical system. The 10mm eyepiece produces only 75×, not enough to show much detail on any of the planets. If you intend to do much planetary viewing with this scope, invest in a shorter-focal-length eyepiece or a Barlow lens. With my 4.7mm eyepiece (160×), the planets looked good, but how was the telescope’s mirror? A star-test showed the diffraction patterns looked much the same on both sides of focus — pretty good, and I wasn’t surprised. Saturn was especially pleasing through the eyepiece. Sky-Watcher’s Freedom Find feature worked well after I went into the Advanced menu on the app and turned the auxiliary encoders on. These are sensors that keep track of the axis’s positions while one or both clutches are released. I moved the tube manually to Saturn and then sent it on a Go To slew to the Moon. It was centred in the eyepiece when the scope stopped, showing that the encoders do their job nicely. The manual states that “enabling auxiliary encoder lowers the resolution of axis positions,” so avoid activating the encoder if you don’t intend to disengage the clutch. How was tracking? An alt-azimuth mount’s tracking accuracy depends on the quality of the Go To alignment. Even with a casual 1-Star alignment, however, the Moon at 75× only needed occasional adjustments to re-centre it. Despite the mediocre eyepieces and stray light problem, I came to love this little telescope. The Virtuoso 150P reminded me that a good 150mm reflector is a powerful and portable performer. So, you can go home again, as I did with this small reflector. The Virtuoso can provide night after night of amazing voyages through the sky and would be a difficult telescope to outgrow. „ ROD MOLLISE scans the night sky from his home in the outskirts of a city. S The SynScan Pro app makes it easy to connect your smart device to the mount by touching the Connect button at the top of the opening screen. Select ‘SynScan 5500’ and in moments your phone is paired and you’re ready to move on to the alignment routines. S There are four different staralignment options to choose from in the SynScan Pro app, though the ones that require two or more stars produce the most accurate results. S After choosing a first alignment star, the app produces an extensive list of choices for the second alignment target, which often includes the bright planets when they are visible. S The SynScan and SynScan Pro apps include a night mode to help preserve your dark adaptation. This screen shows ‘Tonight’s Best’ objects.

www.skyandtelescope.com.au 71 NEW PRODUCT SHOWCASE New Product Showcase is a reader service featuring innovative equipment and software of interest to amateur astronomers. The descriptions are based largely on information supplied by the manufacturers or distributors. Australian Sky & Telescope assumes no responsibility for the accuracy of vendors’ statements. T AUSTRALIAN-MADE ASTROGRAPH Astroworx has released a 25cm (10-inch) f/4 carbon-fibre Newtonian astrograph OTA ($6,499). Designed and made in Australia (except for the mirrors), it has a primary mirror bonded to a six-point floating support system that holds the mirror securely that eliminates the flaring and astigmatism introduced by mirror clip designs. A built-in edge mask provides further enhancement while heavy duty support springs eliminate the need for collimation locking screws. A cooling fan is included. The base-model features a GSO primary mirror and an Antares US-made 78mm (3.1-inch) secondary that is flat to 1/14 of a wavelength. The secondary mirror is supported on a spider milled from a single piece of aluminium; the secondary holder has precision thumbscrews with rounded tips, a built-in dew heater and an independent mirror rotator that enables the secondary to be aligned with the focuser. The 2.5-inch Crayford focuser has a hard-anodised drawtube with M68 female thread and features an integrated Pegasus or ZWO stepper controller compatible with a wide range of equipment and software.  Astroworx astroworx.com.au W APO REFRACTOR Orion Telescopes & Binoculars has added a new model to its line of EON refractors. The Orion EON 90mm ED Triplet Carbon Fibre Apo Refractor (US$1,799.99) is an f/6 air-spaced apochromat that uses Hoya FC-100 extradispersion glass to produce excellent colour correction both visually and photographically. Its carbon-fibre tube measures 45 centimetres with its dew shield retracted. The scope is equipped with a dualspeed, 2½-inch rack-and-pinion focuser that features a built-in camera angle adjuster and can hold a payload of 8.8 kg. The telescope comes with hinged tube rings, a Vixen-style dovetail mounting bar, and metal lens caps. The finderscope dovetail saddle is compatible with Synta-style quick-release finderscopes (not included). Orion Telescopes & Binoculars telescope.com S BIG DETECTOR Camera manufacturer QHYCCD announces a new medium-format model for deep sky imaging. The QHY461PH camera (US$10,800) is designed around the extremely sensitive Sony IMX461 BSI CMOS detector, which has a 11,760 × 8,896 array of 3.76-micron-square pixels measuring 44 × 33 mm. This 102-megapixel, back-illuminated sensor provides native 16-bit A-to-D conversion on chip. Its dual-stage, thermoelectric cooling produces stable operating temperatures of as much as 35°C below ambient temperature. The camera body has a built-in dew heater around the optical window to prevent condensation. Its 77mm aperture mates directly with the company’s CFW3XL filter wheel. Each camera comes with a 2-metre USB 3 cable and CD containing the camera drivers and control software. QHYCCD qhyccd.com

72 AUSTRALIAN SKY & TELESCOPE July 2023 W The mount requires holes for the lens and for the Telrad adjustment knobs. ASTRONOMER’S WORKBENCH by Jerry Oltion The Telrad prescription Ditch the eyeglasses while observing once and for all. ONE OF THE MOST FRUSTRATING aspects of wearing glasses is that you have to take them off to look through most eyepieces, yet you have to put them back on to look through a Telradstyle finder. On-off, on-off all night until you want to throw the glasses away and scan the sky at random. Retired optical research engineer Bob Schalck reasoned that if he could put the correction on the Telrad instead of on his face, he could eliminate the swapping on and off and enjoy observing without distraction. Bob is nearsighted by 3 diopters. Diopters are how opticians measure a lens’ focal length, and it’s a simple conversion to more astronomer-friendly units: Divide diopters into 1,000 mm to get the focal length in mm. So 3 diopters of nearsightedness require a minus-3-diopter lens to correct, so that’s 1,000/–3, or –333 mm. A little hunting online found Bob a 50mm double-concave lens of –300mm focal length. Close enough. In fact, the extra strength of the lens (it’s –3.3 diopters) gives an advantage: At BOB SCHALCK (3) night when our pupils dilate we often become even more nearsighted, a phenomenon called night myopia. Having a little extra power in the corrective lens helps compensate for that. Once Bob had his lens in hand, the next question was how to mount it on the Telrad. These finders have an angled glass window set inside an open-backed framework, so there’s no convenient place to attach a lens. If you had a small enough lens, you could set it on top of the Telrad’s lens, but that would leave the sky blurry when you looked through the window. Bob wanted the sky to be as sharp as the target, which meant putting the lens between his eye and the glass window. The solution seemed obvious: Put the lens on a hinged board that could be flipped up into place or down out of the way. Bob used 3mm plywood and cut the lens hole with a laser, but a Forstner bit would also do the job nicely. He quickly realised that he needed additional holes to accommodate the Telrad alignment knobs. A small hinge at the bottom allows it to flip down out of the way, and a bit of Velcro holds it in place when it’s flipped upward. Bob hot-glued the lens in place and went with screws for the hinge. How does it work? Like a charm! The lens provides just the right amount of correction for Bob to use without his glasses. The Telrad’s scale remains the same, so he can still mark his scope’s aim across the sky by degrees. And he can leave his glasses in his pocket while aiming and viewing through the telescope. For more information, contact Bob at [email protected]. „ JERRY OLTION is thankful for contact lenses. S Left: When upright, the corrective lens enables you to use a Telrad without glasses. Right: With the lens tilted down, the Telrad works normally.

TO SUBSCRIBE TO OUR DIGITAL EDITION – OR TO TRY IT OUT WITH A SINGLE ISSUE – PLEASE GO TO: www.zinio.com/au/australian-sky-telescope-m7176 If you have any questions, please get in touch by phoning 02 9439 1955 (9:00am to 4:30pm, Sydney hours) or email us at [email protected]. As of this issue, Australian Sky & Telescope will be available solely via subscription in digital format on the Zinio platform. I’m a print subscriber? What do I have to do to change to digital? We recently sent you an email or a letter in the post, outlining the simple steps you need to take. If you haven’t received the email or letter, please let us know by phoning 02 9439 1955 or email us at [email protected]. Why the change? The rise of digital subscriptions — particularly during the COVID lockdown period, when a lot of newsagencies were closed — and a consequent drop in sales of the printed edition, means the time has come to go fully digital. With the digital edition, you’ll be able to read your favourite magazine anytime, anywhere on your desktop computer, laptop or tablet. You’ll also get access to the magazine the moment it is published — no more waiting for the postie to come or for newsagent deliveries to arrive. So come and join us on our digital journey! ESO/VPHAS+ team/N.J. Wright (Keele University)

74 AUSTRALIAN SKY & TELESCOPE July 2023 Astro activities for National Science Week There’ll be lots of inspiring and hands-on activities for the whole family. National Science Week is coming up in August, and the federal government has allocated nearly $500,000 in grants to a range of public science outreach activities across the nation… a number of which have an astronomical focus. The National Quantum and Dark Matter Road Trip will be an interactive travelling science and art show, bringing quantum physics, dark matter particle physics and ‘creative expression’ to capital cities, regional and remote areas. Scientists from two ARC Centres of Excellence will visit community hubs in regional Queensland and Victoria, and run public events in other states’ capital cities. Indigenous Science Experience @ Redfern, organised by Macquarie University, will showcase the value of traditional and contemporary Indigenous knowledge in science and technology — including astronomy — and the relevance of science to our everyday lives. The event will bring together First Nations peoples, science academics, and Indigenous and STEM outreach organisations to provide activities for primary school students; there’ll also be a community open day at the Redfern Community Centre. Plus there’ll be online presentations and workshops for people elsewhere in Australia. Science in the Swamp – Superpowers of Nature, presented by Centennial Park and Moore Park Trust, will take place at Sydney’s Centennial Parklands. It will comprise free, hands-on, outdoor family and community activities including daytime astronomy. There’ll be plenty of biology and ecology, too, as the event will focus on nature’s ‘superpowers’ — which animals are the fastest, the strongest, have the best vision or the best hearing? You’ll be able to wander the wetlands, ID a frog and meet Centennial Park’s bats. The University of Wollongong will present Science Showcase UOW, an evening in the planetarium that will feature a presentation exploring the Universe… from the roles of molecules to Indigenous astronomy. Plus there’ll be guided tours of science labs and research spaces, and an opportunity to meet top local scientists. The Endless Universe Show will comprise six live performances at the Melbourne and Brisbane Planetariums, with artist-scientist Jenna Robertson exploring such questions as: How long will humans be able to live on Earth? What cosmic endings and new beginnings await humanity? How do we make sense of all of this? Through a poetic integration of science and art, the work will aim to inspire human belonging and purpose within the wonders of astronomy, astrophysics and cosmology. At Footy Oval Astronomy at the Mount Burnett Observatory (Melbourne), volunteers will take over an AFL oval to run this free event for the local community and emergency services volunteers, bringing the wonders of astronomy to a wide audience, in person and online. Telescopes will be on hand to show visitors the night sky and demonstrate that astronomy is accessible to everyone. This will be complemented by indoor activities including astronomy talks, computer simulations of the night sky and objects of interest, information on Indigenous astronomy, a live Facebook stream to enable questions and answers throughout the night, a live band and food vans. The three-hour event will be broadcast via Facebook and on free-toair television by Channel 31. You can find more details about these and other events at scienceweek.net.au. NIGHT LIFE ESO/L. CALÇADA/SPACEENGINE.ORG

www.skyandtelescope.com.au 75 by Diana Hannikainen PRO-AM COLLABORATION RON MILLER / NASA We know that rings encircle the giant planets in our Solar System — Jupiter, Saturn, Uranus and Neptune all orbit the Sun accompanied by an entourage of rings. We also know of more than 5,000 confirmed exoplanets today, many of which are giants. It follows that they’d have rings, too. But exoplanets are many lightyears away and hard to find in their own right. If they’re so tough to spot, how can we go about finding their rings? Matthew Kenworthy (Leiden University) is taking a unique approach to this task. And he has called upon the amateur community to help him out. Big, big rings. While examining archival data of the young star J1407 (short for 1SWASP J140747.93- 394542.6), Erik Mamajek (University of Rochester) and his graduate student at the time, Mark Pecaut, noticed that it exhibited a series of complex eclipses over a period of about two months. Kenworthy’s subsequent analysis showed that not only was the star’s dimming likely due to an unseen substellar companion — dubbed J1407b — passing in front of the star from our perspective, but the model that most satisfactorily fit the data pointed to a ringed exoplanet. Further analysis Explore exorings The hunt for rings around other planets is on. revealed that the ring system is huge, with some 30 rings spanning around 120 million kilometres in diameter. That’s about the size of Venus’s orbit around the Sun. We can’t see exorings directly, but instead light from the star acts like a backlighting torch. If we can detect this starlight, then we can measure the distribution of material around the companion, which could tell us how much gas and dust there is and whether there are clear clumps or gaps that might be caused by moons. Finding suitable candidates for further study, though, proved challenging. But one day a friend of Kenworthy’s tagged him on, of all things, an ASAS-SN Twitter post. The All-Sky Automated Survey for Supernovae automatically surveys the entire sky every night down to about magnitude 18. As its name implies, it’s mainly primed to search for new supernovae and other transient events. But the event Kenworthy’s friend had pointed him to was no supernova: A star, named J0600 for short, had started exhibiting complex eclipses. Amateurs help out. The stars that Kenworthy is after are very similar to our Sun. They’re on the main sequence and are “quiet and boring for a few years until they undergo these weird dimming episodes,” he says. Professional telescopes’ finite time is largely dedicated to observing the faintest objects in the sky — it’s tough to get them to consistently observe other targets. And so for his objects of interest, which at around magnitude 12 or so are well within reach of amateur scopes, Kenworthy turned to the American Association of Variable Star Observers. The support of the AAVSO is crucial: The data are not only immediately available, but the different wavelengths tell us the nature of the material passing between us and the star. If more blue light is blocked than red, we know there’s dust. Once this information is in hand, coupled with detections of weird eclipses, Kenworthy turns to the big professional telescopes for targeted data. He’s currently writing a paper on J0600 — and among the coauthors are several AAVSO observers. Kenworthy notes that spitting out weird light curves is not ASASSN’s primary goal (remember, it’s supernovae they’re after). “But to me it’s gold dust,” he says. “Because they’re willing to share their data, it’s opening up a brand-new subfield. We couldn’t have done this 10 years ago.” The combination of the internet (including social media), able amateurs and the surge in citizen science is enabling this fun and curious new science. If you’re interested in looking for exorings, keep an eye on https://is.gd/ aavso_campaigns. And, if you happen to spot unusual flickering, make sure you let Kenworthy and his team know. „ DIANA HANNIKAINEN is fascinated by planets’ Hill spheres. W SUPER SATURN Saturn’s rings are very close in to the planet, within its Roche radius. But the Hill sphere is where the gravitational influence of a planet is stronger than that of its star (and is much bigger than the Roche radius). Material in the Hill sphere of a young planetary system is a vast structure, such as that of J1407b (above), which is some 200 times more extensive than Saturn’s rings. If Saturn had such rings, it would appear as large as about 10 full Moons!

WITCHY WONDER Fernando de Menezes IC 2118, the Witch Head Nebula, is a faint reflection nebula in Orion. It’s thought that illumination by starlight from Rigel might be responsible for its dim glow. RA: 05h 02m Dec: –07° 54´ DETAILS: Sky-Watcher 150mm Esprit, cooled ZWO ASI6200MC camera, 55 hours total exposure. READERS’ GALLERY 76 AUSTRALIAN SKY & TELESCOPE July 2023

www.skyandtelescope.com.au 77 HOW TO SUBMIT YOUR IMAGES Gallery showcases the finest astronomical images that our readers submit. Send your best shots to [email protected]. See skyandtelescope.com.au/contributions/ for guidelines. S CRATERED FACE Kim Brkic Proving that planetary video cameras can produce excellent results, this image of the Moon shows our neighbouring world’s craters and hills in dramatic detail. DETAILS: Celestron CPC 925 telescope, GSTAR-EX3 camera, 40-second exposure. W LUNAR LIGHT William Lelyveld You don’t need a telescope in order to image the Moon. William simply used the COOLPIX’s Moon exposure setting with its built-in blue filter. DETAILS: Nikon COOLPIX P1000 camera, 1/320-second exposure.

READERS’ GALLERY 78 AUSTRALIAN SKY & TELESCOPE July 2023 CLOUDY NIGHTS Sean Liang The Chamaeleon Cloud Complex is a region of dense nebulosity that is spawning a new generation of stars on the edge of the ‘Local Bubble’ in the Orion Arm of the Milky Way. It spans the southern constellation Chamaeleon and reaches into several adjacent constellations. DETAILS: Takahashi FSQ-106ED scope and FLI PL16803 camera via Telescope Live.

www.skyandtelescope.com.au 79

80 AUSTRALIAN SKY & TELESCOPE July 2023 READERS’ GALLERY W GLORIOUS GLOB Paul van Leuven One of the showpieces of the southern skies, and certainly the finest (and definitely the biggest) of the Milky Way’s globular clusters, Omega Centauri is around 17,000 light-years from Earth. RA: 13h 27m Dec: –47° 29´ DETAILS: Sky-Watcher Esprit 100ED telescope with diffraction-spike mask, QHY294 PRO camera, 9 minutes total exposure. CARINA’S COUSIN Kevin Fox Located about 7,600 light-years from Earth on the northwest edge of the Carina Nebula, is the start cluster NGC 3324 and the associated nebula Gum 31. The star cluster was first catalogued in 1826 by James Dunlop, observing from the environs of Sydney. RA: 10h 37m Dec: –58° 38´ DETAILS: Meade LX850 scope, Canon EOS Ra camera, 30-second exposure.

www.skyandtelescope.com.au 81 CARINA CLUSTER Davide Mancini Very close (in stellar co-ordinates) to NGC 3324 (see previous page), lies NGC 3293, an open star cluster in Carina. It was discovered by Nicolas-Louis de Lacaille in 1751. RA: 10h 35m Dec: —58° 14´ DETAILS: SharpStar 150 astrograph, ZWO 2600MC camera, total exposure of 51 hours.

82 AUSTRALIAN SKY & TELESCOPE July 2023 FOCAL POINT by Robert Richard LEAH TISCIONE / S&T mounted and used for the benefit not only of myself but of the residents, employees and their families? In March 2019 I presented my idea to the complex’s CEO. Happily, he thought it was a grand idea. With his blessing and that of the entire staff, I began to work out the details of constructing and operating an observatory to house my scope and all its ancillary gear. As with any intricate project, unforeseen difficulties arose. COVID and supply-chain problems delayed things, and assembling the Technical Innovations 3-metre-diameter dome observatory took longer than anticipated. But in early 2022 our crew completed the dome and installed the scope. A key part of the observatory is the ‘observing room’ located in a lounge area inside the main building near the dome. Through a home network, we use a program that allows me to display real-time images from the scope’s video camera on four large-screen TVs hung on walls around the room. In this way, all residents, regardless of mobility restrictions, can savour astronomical An observatory for seniors The author’s brainstorm brought deep satisfaction to his retirement community — and to himself. THERE WAS A PROBLEM… a big one. At 68 I retired from a busy private practice in psychology. I enjoyed my work, and it was with mixed emotions that after more than 34 years I decided to leave to focus on other interests. In April 2018 my 80th birthday rolled around. That landmark event prompted my wife and me to begin serious discussions about where we wanted to live in our final years. We decided the best path for us was to move into a retirement village near our home. And the problem? I’d been using our backyard for imaging with my new 28cm (11-inch) Celestron EdgeHD scope. Moving to the village presented me with the serious issue of where to use my telescope. The staff made it clear there was no place to leave my instrument set up overnight. At my age, setting up and taking down a scope of this size whenever I wished to image is a definite deterrent to enjoying my hobby. But then I had an idea that changed the entire landscape for me… and for everyone at the retirement village. How about building an observatory where my telescope could be permanently sights while seated in a climatecontrolled environment. We display images both from my telescope and downloaded from professional observatories such as the James Webb Space Telescope. To help me operate the observatory, I recruited six residents to become ‘assistants’. They completed a sevenweek observational astronomy course I taught. As time goes on, we continue to improve the operation. Recently we mounted an 80mm solar scope on the main telescope and can now observe sunspots and prominences. The observatory has had a very positive impact. Many residents, I learned, had never looked through a telescope. Their excitement and gratitude for being able to do so now is tangible. Sharing my decades of knowledge with others in my age group has been deeply meaningful. I hope my experience inspires other amateurs in retirement communities to do the same. „ Now 85, DR. ROBERT RICHARD is a lifelong amateur astronomer.

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