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Southern Cross - June 2002

• The Origins of Our Society Badge by Gerry Kellock
• Scorpius by Albert Brakel
• 1512 OULU-Another Occultation Success by Albert Brakel
• The Bennett Catalogue - Part 2 by Jenni Kay

The Origins of Our Society Badge

Gerry Kellock

Around 1972, and probably following the NACAA, which had been held in Melbourne that Easter, it was decided by the then Committee that the Canberra Astronomical Society should have a badge. I have no clear recollection of this, but I believe that it may have been prompted by the custom of exchanging society badges at NACAAs in those days.

At the Committee discussion it was suggested that an incentive in the form of a prize should be awarded to the winner, and a 14-inch (35.5 cm) square contact print taken by the Schmidt telescope of the Large Magellanic Cloud was obtained for that purpose.

I duly relayed the requirements to an artistic friend who worked with me in the Department of Defence, and extolled the virtues of his winning a photo taken by the famous UK Schmidt telescope at Siding Spring. Since I recollect that he had never shown any interest in my hobby previously, I suspect that the possibility of winning this prize was no great incentive. However, very quickly he came back to me with a drawing, and I handed it to the Committee.

I cannot recall the designs of any other contestants, or indeed how many designs were entered, but I recall that the winning design was unanimously agreed to be best.

What he used for inspiration I have no idea. My efforts to contact him have failed, but I recollect having asked him a similar question soon after his winning, and I think his answer produced nothing tangible. Why, for instance he should have used an ancient-Egyptian-like figure at his telescope when, in fact, the telescope was almost certainly invented much later and by Europeans, I have no idea. It is however an eye-catching, yet simple, design and I hope the Society continues to use it well into the future.

For the record, the name of the designer of the CAS badge was Timothy M. Anderson, and he was employed in the 'seventies by the Department of Defence (Navy) as an electrical design engineer.

[The logo at the top of this web page is artwork based on the original design - web master]

Scorpius

Albert Brakel

After the Southern Cross and Orion, Scorpius must be the most generally recognized of all the constellations. In mythology, it represents the scorpion that stung Orion on the heel and killed him. Over the millennia it has also been known as Scorpios and Scorpio, but the spelling is now fixed as Scorpius, at least as far as astronomers are concerned.

Lying in a rich part of the Milky Way, Scorpius is well endowed with open clusters, stacks of globular clusters, planetary nebulae and double stars, and some emission nebulosity, but there is also a lesser downside - light absorption by dust in the galactic disk causes some objects to be fainter than they would otherwise be, and there are no galaxies.

The brightest star is fiery-colored Antares (RA 16h 29.4m, Dec -26° 26'), a giant about 700 times the diameter of the Sun. It has a mag. 5.4 companion 2.9" to its west, which is normally so overwhelmed by the glare of the primary that it can't be seen, unless the primary is dimmed somehow. I first saw it in bright twilight through thin haze with 8" aperture, when it appeared white, its true color. On another occasion, when I was using the Oddie telescope and the whole sky clouded over, Antares was the only object still dimly visible through the cloud, so I took a look and there was the companion again, but this time it was a bright grass-green! The effect was an illusion caused by color contrast with the red primary (the complementary color of red is greenish), but it was stunningly pretty all the same.

Now shift your gaze to Delta (δ) Scorpii (16h 00.3m, -26° 17'), the middle star of the "claws" of the Scorpion. Normally the three stars of the claws are about equal in brightness, but since July 2000 Delta has got noticeably brighter for reasons that are unexplained, rising from mag. 2.3 to about 1.6. Usually the second-brightest star in Scorpius is Shaula (Lambda [?] Sco) at the tip of the tail, but at the moment it's Delta, which used to be the fifth brightest.

For the telescopic views, I used a 20 cm (8") SCT from my Downer backyard, to see what the average suburban astronomer can expect.

Globular clusters

M4 (16h 23.6m, -26° 32'): This well-known globular cluster is visible with binoculars or a finder scope. With 77x it presented a loose irregular halo of stars, with the core unresolved except for a prominent bar of stars across it. The central region was still unresolved with 117x, but showed graininess with 154x, and some faint stars with 190x. It was not completely resolved even with 235x. At about 6500 light years distant, M4 competes with NGC 6397 in Ara for the title of the closest globular to Earth; various publications disagree on this, but the latest information suggests that M4 is closer by a whisker.

M80 (16h 17.0m, -22° 59'): A small, reasonably bright globular with a marked central concentration. On the night I last looked, graininess was apparent with 117x and higher powers, but it could not be resolved with any magnification, even though the seeing was good enough to split the four components of Nu Scorpii.

NGC 6144 (16h 27.3m, -26° 02'): Quite close to Antares, this cluster is fairly faint and finds it hard to compete with even moderate light pollution. Nor does the diffuse nebula around Antares help. The core is not particularly concentrated, and appears as a dim roundish haze with a faint star on its western edge. It began to look a bit grainy with 154x.

NGC 6139 (16h 27.7m, -38° 51'): Slightly smaller than 6144, but with a bright very condensed centre surrounded by a diffuse circular glow that is affected by light pollution. Difficult to resolve into stars because of interstellar absorption.

NGC 6388 (17h 36.3m, -44° 44'): Near the southern border of Scorpius, this is an easy, well-compressed globular 3.5' across, that looks very nice in a field of surrounding moderately bright stars. It was not resolved even with 235x. A moderately faint foreground star is parked in front of its northern outskirts.

Tonantzintla 2 (17h 36.7m, -38° 33') is only 6' NW of the star Q Scorpii. A small 1' across, and faint (mag. 12.2) because of intervening dust, I could not see it, but perhaps those with larger 'scopes and better skies might like to try for it.

NGC 6441 (17h 50.2m, -37° 03'): This is one of my favourite globulars in Scorpius, even though it is rather small (2') and unresolved. What makes it special is the color contrast between the soft white globular and the bright mag. 3.2 orange star G Scorpii 4.5' to the west.

Had enough globulars for now? Then lets have a look at something else ...

Open clusters

NGC 6124 (16h 25.6m, -40° 40'): An open cluster not as splashy as some in Scorpius, but not bad all the same. It contains scattered stars without any concentrations, and there are some apparent pairs and groups. Some stars are pale orange, which would have had a more intense color if the stars had been brighter or if I'd used a larger aperture.

NGC 6231 (16h 54.0m, -41° 48'): This cluster is one of the glories of Scorpius, and a favorite for showing at public viewing nights. Its stars have a range of brightnesses, which makes it attractive, and three white stars in the middle are particularly bright. It is very effective at low magnification, and through small telescopes.

NGC 6242 (16h 55.6m, -39° 30'): Although about 10' across if the scattered outermost members are taken into account, the brighter stars are mostly gathered into a N-S elongated area only about 5' long, except for the very brightest one, which is orange and located south of the concentrated group.

NGC 6281 (17h 04.8m, -37° 54'): The most striking thing about this open cluster is its squat triangular shape, and how the 17 or so brightest stars are lined up to form the sides of this triangle. Most unusual.

M6 (17h 40.1m, -32° 13'): This is the famous Butterfly Cluster, whose characteristic shape can be picked out with 7x binoculars. Telescopically, it is dominated by medium-bright stars, with some fainter ones, arrayed in arcs and loops. The brightest one is orange, set on the NE side, and is actually the irregular variable BM Scorpii (mags. 5.8-8.1, period 850 days). The cluster is seen to advantage with both 50x and 77x powers. 50x best shows the contrast between the dense cluster and the sparser surrounding star field, while with 77x it filled much of the field of view (26' of a field of 40') and the stars appeared brighter.

M7 (17h 53.9m, -34° 49'): As one of the brightest open clusters in the sky, it is obvious to the unaided eye, and makes a good binocular object. 77x magnification shows the central region to advantage, but a drop down to 50x is needed to show most of it (except for the outlying members). It is dominated by medium-bright stars, many of which are aligned in near-straight lines. The faint and distant globular cluster NGC 6453 lies near the NW edge of M7, but because it appears like a mag. 11 spot of grainy nebulosity only 1' across, this was too much of a challenge in my suburban sky.

Planetary Nebulae

NGC 6153 (16h 31.5m, -40° 15'): Finding this reasonably bright (mag. 10.9) planetary nebula is greatly helped by its location at the southern corner of a small rhombus, which it forms with an orange star, a white star and a close double. The double was barely resolved with 235x. At low power (77x) the nebula looked like a blurry blue-grey star, but this became an obvious disk with 154x. The unusual star pattern and the color contrasts make this a rewarding target.

The Bug Nebula, NGC 6302 (17h 13.7m, -37° 06') has a high surface brightness, so it was obvious as a concentrated, elongated (1.5') object that was fuzzy and unstarlike even with direct vision. It stood out dramatically with an OIII filter. It gets its name from its insect-like appendages in photos. The Hubble Space Telescope image is spectacular, showing a bipolar nebula with angular spikes coming off.

NGC 6337 (17h 22.3m, -38° 29') was described by John Herschel as "a beautiful delicate ring of a faint ghost-like appearance". I can testify to its wraith-like quality, as I needed an OIII filter to find it, through which it appeared as a tenuous ring 40" across. The HB Astroatlas chart D12 was indispensable as a finder chart. Once I knew exactly where it was, I could detect a very vague 'something' at the location without the filter.

Emission Nebula

NGC 6334 (17h 20.5m, -35° 43'): Variously called the Cat's Paw or The Footprints, this nebula complex shows up on photos as a group of roundish glows of red hydrogen alpha light. It would be rated one of the wonders of the sky, were it not that the visible light wavelengths are greatly attenuated by foreground dust. It can be glimpsed dimly through 20 cm or larger apertures from a dark site, but in my suburban sky it was invisible.

Double stars

As you'd expect from its location astride the galactic equator, Scorpius is thick with double stars, and Antares has already been mentioned. Here is a sampling of some of the best.

2 Scorpii (15h 53.6m, -25° 20') is a binary with an orbital plane edge-on to our line of sight. The separation of 2.3" is slowly closing (it was 3.1" in 1902). The stars are bluish (mag. 4.7) and white (m.7.1).

Beta (ß) Sco (a.k.a. Graffias) (16h 05.4m, -19° 48') is a bright, blue pair (m. 2.6 and m.4.9) set a wide 13.6" apart so it's easy in the smallest telescope. The system has three invisible components, making this a quintuple.

Brisbane 11 (16h 09.5m, -32° 39'): This fine deep yellow and pale yellow pair was one of many doubles discovered by Thomas Brisbane at the former Parramatta Observatory in the early 19th Century. The magnitudes are 6.6 and 7.4 with a generous separation of 7.7".

Nu (ν) Sco (16h 12.0m, -19° 28') is the southern equivalent of the Double Double in Lyra, but not as easy. Low power discloses two stars of apparent magnitudes 4.0 and 6.3, but increasing the power first splits the secondary into m.6.8 and m.7.5 components 2.3" apart, and then if conditions are suitable, the primary parts into m.4.1 and m.6.2 stars 1.3" distant.

12 Sco (16h 12.3m, --28° 25') is a m.5.8 and m.8.0 pair at 3.8". It has white and orange stars, but according to the spectral type the latter should be yellow, indicating a degree of "reddening" by interstellar dust absorption.

h4850 (16h 24.7m, -29° 42') is another good one for small scopes. It consists of two yellow suns of magnitudes 5.8 and 6.6 separated by 4.8".

h4889 (16h 51.0m, -37° 31'): An unequal m.6.2 and m.8.5 white pair that is easy because of the wide 6.7" separation.

Howe 86 (17h 13.9m, -38° 18'): Yellow (m.6.9) and orange (m.8.9) stars at a distance of 2.8" that have been "reddened" by interstellar absorption.

h4926 (17h 14.5m, 39° 46') is a triple system consisting of a bright m.6.6 orange primary (the variable star V915 Sco) with two faint white companions (m.10.5 and m.11.3) that are fortunately situated far enough away at 14.9" and 16.9" so as not to be overwhelmed by the glare of the big star. These other two components lie to the NW and SW respectively.

MlbO 4 (a.k.a Burnham 416) (17h 19.0m, -34° 59'): Another triple system, it has two m.6.3 and m.7.3 orange members in a 42.2-year orbit so that the separation varies from 0.5" to 2.1". The third member (m.10.3) is located a large 31.4" away to the SE.

There are more objects, of all the five types, available in Scorpius. Those described above are only the pick of the bunch. If your appetite has been whetted for more, a decent sky atlas will help you find them.

[Sky map produced using Starry Night Pro 3.12]

1512 OULU-Another Occultation Success

Albert Brakel

At 11:51 pm AEST (13:51 UT) on 2002 May 7, the asteroid 1512 Oulu occulted a magnitude 11.6 star in Libra, and the ground path from which the event was visible passed directly across Canberra, as predicted by an astrometric update posted only days before. Four CAS observers monitored and timed the event: David Higgins in Ngunnawal, Albert Brakel in Downer, Patrick Purcell in Chapman, and Vello Tabur in Wanniassa. The results, and possible interpretations, are shown in the accompanying figure (the circles indicate the minimum sizes for circular objects).

The maximum predicted occultation duration was 7.1 seconds, exactly what Vello observed from his site, showing that the prediction was spot on. The profile obtained for the northern hemisphere of the asteroid clearly indicates that the body is not circular. As there were no chords obtained for the southern hemisphere, we can only speculate about its shape there.

However, you'll notice two strange things about the results. I got a 2.2 sec. occultation 1.5 sec. before my main event, and Patrick's 5.0 sec. event does not fit in with the others, although it overlaps them. The 2.2 sec. disappearance was distinct and unmistakable, and can most likely be explained as a satellite of the main asteroid (there are at least 22 satellites of asteroids definitely known now, and more are being confirmed on a regular basis). This satellite, if it exists, cannot be circular, because then David Higgins would have seen its occultation too. The dashed line interpretation in the figure is just one of many outlines possible.

Another, less likely, possibility is that the 2.2 sec. event was caused by a projection on an irregularly shaped body, such as suggested by the dotted lines. Some asteroids do have irregular shapes, e.g. the banana-shaped Geographos, the dumbbell-shaped Toutatis and Castalia, and the weirdly dog-bone-shaped Kleopatra. Patrick's partly discordant result is more difficult to explain, lying as close as it does to Vello's chord. His optical system was operating at its limit for the conditions, and there was some trouble with atmospheric effects.

Thanks to all the observers who got out and made the effort. This is the first time an occultation by this asteroid has been observed anywhere, so this is the first indication of its non-circular shape. The ground path also passed just north of Auckland NZ, but no potential observers in that region have reported in yet.

In case you're wondering about its name, the asteroid was discovered in 1939 by H. Alikoski, who named it after the town in northern Finland where he was born.

The Bennett Catalogue - Part 2

Jenni Kay FRAS

In the April issue we began a project making visual observations of deep sky objects from the Bennett Catalogue. To briefly recap on the background of this catalogue; Jack Bennett compiled a list of 152 southern NGC objects, that appear "comet-like" through his 5-inch low-powered refractor, with the purpose to help others not mistake these objects for comets in comet searches. For more information please refer to Southern Sky magazine, May/June 1995, page 34.

The following observations were made with either an 8" f/6 Newtonian, or 12.5" f/5 Newtonian from my semi-rural home site in Lobethal, SA. Typically the skies here have a limiting naked eye magnitude of 6.1 with the seeing rated at Antoniadi II-III.

Ben 46 - Hya

NGC 3621 : 11 18.3 -32 49 GX

12.5" f/5 Newt. Easy to locate the field being a short star hop, 3.25 degrees west-northwest of Xi Hya. 83X: Very obvious - very bright, large, much extended north-northwest to south-southeast, with a bright, round core. There is a 13th magnitude star at the northwestern tip. 150X: Much improved - very bright, 5.0' x 2.0' in size, with a high surface brightness.

Ben 47 - Car

Mel 105 : 11 19.7 -63 30 OC

12.5" f/5 Newt. 105X: Obvious - small concentration of very faint stars, where direct vision detects it as an unresolved hazy mass, and averted vision catches brief flickers from numerous stars over the glow. 150X: Improved view - there are twenty stars resolving, the brightness ranges from 12 - 13 mag. to unresolved haze. The cluster is 3.0' in size. Overall, the cluster appears quaint and delicate.

Ben 48 - Cen

NGC 3960 : 11 50.9 -55 41 OC

12.5" f/5 Newt. 105X: Very obvious and dainty little cluster set in a very rich star field. The cluster appears as a slight concentration of a few stars, all similar in brightness at around 12 magnitude. Basically, the stars are arranged in a few long curving chains much like a dangling necklace, and lying in a direction east to west. The cluster is not very rich, not very large, somewhat concentrated, well detached, charming and certainly worthy of note. 150X: There are thirty stars involved, 5.0' wide x 3.5' long (N-S), with two long chains and a couple of short rows of stars. Overall, the leaving impression is soft, delicate and dainty.

Ben 49 - Hya

NGC 3923 : 11 51.0 -28 48 GX

12.5" f/5 Newt. 83X: Obvious - bright, small, little elongated hazy core brightening to a stellar nucleus, all within a relatively large, relatively faint, oval shaped halo. 150X: Improved view - very bright, small nucleus, 20" in size, within a bright core, 1.5' x 30", and a relatively faint halo 3.5' x 1.0'. The major axis lies NE - SW, the galaxy has a high surface brightness, and there now and then I can catch a very faint superimposed star lying west of the nucleus. In general, this galaxy is a bright and easy enough to be included in any list of glossy objects.

Ben 50 - Mus

NGC 4372 : 12 25.8 -72 40 GC

12.5" f/5 Newt. 8x50mm finderscope: Obvious - relatively faint, small, round hazy spot. 105X: The view is rather breathtaking - the cluster is a bright, large, round glow with numerous 13 mag. stars strewn across it, and more others spilling long passed the edge of it. 150X: Improved view - very bright, rich and tight central region is 4.0' in diameter, while the entire cluster out to the far reaching outliers stretches to 10.0' in size. There are easily fifty stars resolved well, and a brilliant 7 mag. field star lies at the NW edge.

Ben 51 - Hya

NGC 4590 (M68): 12 39.5 -26 45 GC

12.5" f/5 Newt. 83X: Impressive sight - bright, large, round, hazy glow with numerous stars resolved across the glow and then extending past the edges as loose stragglers. The background cluster glow is granular to near resolving right to the core. 150X- Splendid - bright, large, round, glow plus stars. The very compact core region is 4.0' in size, while out to the edge of the stragglers is 5.0'.

Ben 52 - Vir

NGC 4594 (M104) : 12 40.0 -11 37 GX

"The Sombrero Galaxy" 8" f/6 Newt. 9x50mm finderscope: easy enough to detect with care appearing as a soft, relatively faint, small, oval glow. 50X: More obvious - bright, long, slim hazy spindle with a bright, small, round core. 80X: Much more interesting - can now see the shape of the sombrero hat, with the galaxy showing a very flat edge on one side. In moments of steady seeing, this flat edge becomes a thin, dark lane with a little more of the galaxy showing on the other side. Overall, the galaxy is bright, with a central bulge, a very bright, small round core, and the dark lane. It has a high surface brightness, the size is 6.0' x 1.5', major axis lies east to west, and the round, core is 15" in size. The galaxy also looks like a Hollywood type "flying saucer". This galaxy is a favourite sight for many observers.

Ben 53 - Vir

NGC 4697 : 12 48.6 -05 48 GX

8" f/6 Newt. 80X: Very obvious - very bright, relatively small, oval shaped core, within a large, very faint, oval halo. Adding to the overall striking general view, there is a prominent line of four 9/10 mag. field stars south of the galaxy. 120X: Much improved - very bright, very small, oval nucleus 25" x 20" in size, within a bright core 50" x 30", and the relatively faint halo 1.0' x 30" in size. The major axis lies NE - SW, and the galaxy has a high surface brightness.

Ben 54 - Vir

NGC 4699 : 12 49.0 -08 40 GX

8" f/6 Newt. 80X: Very obvious - very bright, relatively small, round core within a relatively large, relatively faint, round - oval shaped halo. 120X: Similar view - there is a very bright, very small, round nucleus 20" in size, a very bright, round core, 30" in size, and a relatively faint, oval halo, 2.0' x 1.0' in size, major axis lies NE - SW, and the galaxy shows a smooth, high surface brightness.

Ben 55 - Vir

NGC 4753 : 12 52.4 -01 12 GX

8" f/6 Newt. 80X: Bright, easy and attractive - bright, small, round core, within a relatively bright, relatively large, oval - elongated halo. In the wider, general view there are five bright 10-mag. field stars, a handful of fainter, a smooth dark background sky and this very eye-catching galaxy. A most attractive sight! 120X: Improved view - bright oval core, 45" x 30" in size, gradually brightening to an almost stellar nucleus, all within a relatively bright halo, 1.5' x 35" in size. The major axis lies ENE - WSW and the galaxy has a smooth, high surface brightness.

Ben 56 - Mus

NGC 4833 : 12 59.6 -70 53 GC

12.5" f/5 Newt. The cluster offers an impressive sight and is easy to locate being almost one degree north of Delta Muscae. 83X: Very obvious - bright, relatively large, granular haze, with many far-reaching outliers. 105X: There are at least one hundred 13-magnitude stars resolving well, and scattered across the haze and further. Overall, the cluster is round, 10.0' in diameter, with a bright, very condensed region being about 4.0' in size.

Ben 57 - Cen

NGC 4945 : 13 05.4 -49 28 - GX

12.5" f/5Newt. 66X: Very obvious - bright, very long and broad, with a smooth and even glow throughout, and set in a rich starry field. 150X: Improved view - bright, 20.0' x 3.0' in size, high surface brightness, with the major axis lying northeast to southwest. NGC 4976 lies nearby to the east. A favourite sight among many southern galaxy hunters.

Ben 58 - Cen

NGC 4976: 13 08.6 -49 30 - GX

12.5" f/5 Newt. 31.5' east of NGC 4945. 105X: Very obvious, and wouldn't miss it - very bright, relatively small, round, hazy spot, with a softer, relatively bright oval shaped halo. 150X: Improved - very bright, round core, 20" in size, within an oval halo, 70" x 40" in size, with the major axis lying north-northwest to south-southeast. Overall, the galaxy has a high surface brightness.

Ben 59 - Hya

NGC 5061 : 13 18.1 -26 50 - GX

8" f/6 Newt. 80X: Bright and easy - very bright, very small, almost stellar nucleus, with a bright, small, round halo. 120X: Similar view - very bright, stellar nucleus, equal in brightness to an 11 mag. star, within a bright, round halo 35" in size. The galaxy has a high surface brightness and a smooth glow throughout.

Ben 59a - Vir

NGC 5068 : 13 18.9 -21 01 - GX

8" f/6 Newt. 80X: Obvious enough - relatively bright, very large, round to oval shaped, smooth hazy glow, with a bight, small round core, and 1 faint superimposed field star. 120X: Improved view - Relatively bright, round, 4.5' in size, with a bright, round core, 50" in size, and there is one 14-mag. field star NE of centre. Overall, the galaxy has a high surface brightness.

Ben 60 - Cen

NGC 5128 : 13 25.5 -43 01 - GX "Centaurus A"

8" f/6 Newt. 9x50mm finderscope: obvious - bright, small, round, hazy glow. 80X: Stunning view - bright, very large, round, with a wide, very dark lane through the centre running almost northwest to southeast. Due to its appearance, the galaxy is frequently dubbed the "hamburger". There are two superimposed stars on the galaxy, one near the centre, the other near the dark lane edge. 120X: Overall the galaxy is bright, round, 6.0' in size, with the dark lane being 40" in width. Now and then I can detect some milkiness, or wisps within the dark lane. In general, this object is another southern favourite of many observers.