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Canberra
Astronomical Society
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Southern Cross - July 2003
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COTM:
CONSTELLATION OF THE MONTH – LIBRA
Albert Brakel
Libra the Balance or Scales is well-known as
a constellation of the Zodiac, but it is not one of the most
striking ones. It has only two stars, Alpha and Beta, that could
be called reasonably bright, at magnitudes 2.7 and 2.6; these
are sometimes called the Gateway Stars, because the planets
in their travels around the Zodiac usually pass between them.
The constellation was the last to be recognized in the Zodiac,
in Roman times when the Sun was in it on the northern autumnal
equinox, when day and night were in balance. Previously, the
stars had been assigned to the claws of Scorpius, and this is
reflected in their delightful common names of Zubenelgenubi
(the Southern Claw) for Alpha, and Zubeneschamali (the Northern
Claw) for Beta.
The Scorpius-Libra combination is thought to have been the last
relic from more ancient times, when the Zodiac is believed to
have been divided into only six constellations. Another example
may have been Taurus, which these days only represents the front
part of the Bull, the former hindquarters being used to form
Aries.
Alpha Librae (RA 14h 50.9m, Dec. -16°
02’ 30”) is an easy double in binoculars. The components
are almost 4’ apart, and the companion star is mag. 5.2.
The stars have the same proper motion.
Unless you’re a faint galaxy fan (all the galaxies are
fainter than mag. 11), the only deep sky objects in Libra apart
from double stars are a globular cluster and a planetary nebula.
At least the double stars are readily accessible from a less-than-dark
suburban backyard. The least-faint galaxy by the way, is NGC
5728 (14h 42.4m, -17° 15’), that glows at
mag. 11.3 and shows on long-exposure photos as a fine barred
spiral with its inner region displaying a theta-shape. In a
telescope with a dark enough sky though, all it shows is a core
surrounded by a faint haze. But now for easier game.
Merril 2-1, a.k.a. VV 72 (15h 22.3m, -23°
38’) is a planetary nebula that has a higher surface brightness
than its magnitude of 11.6 might suggest, because the light
is concentrated into a near-stellar point of light only 6”
across. From my backyard with a 20 cm SCT and OIII filter it
was easy enough, thanks to a useful yellowish mag. 10 star only
1’ to the west. Blinking with the filter alternately shows
the nebula brighter or fainter than the star. Only with high
magnifications does the object appear fuzzier than a normal
star.
NGC 5897 (15h 17.4, -21° 01’) is
a loose, poorly-concentrated globular cluster that lives up
to its reputation of being sensitive to any light pollution.
I not only had to contend with the usual sky glow, but with
the light of a nearby First Quarter Moon (my first opportunity
after about 3 weeks of continuous cloud). When I found it, it
appeared as a very faint glow across an area about half a Moon
diameter wide. With averted imagination, I might have intermittently
seen 2 or 3 stars imbedded in it. This is definitely not a showboat,
and only the most ardent globular devotee could say they love
it. I agree with the guide that says “the challenge here
lies in simply finding the object”.
And now for some telescopic binaries. Struve 1837
(14h 24.7m, -11° 40’) is a pale yellow, close unequal
(mags. 6.7 and 8.3) pair 1.3” apart, requiring steady
seeing for a good split.
South 179 (14h 25.5m, -19° 58’)
presents as a wide (35”), almost equal (mags. 6.6, 7.0)
white twosome, but the greater interest is in resolving the
fainter star, which itself is the binary Burnham 225, with mag.
7.3 and 8.5 stars at a close 1.2”.
Iota Librae (15h 12.2m, -19° 47’)
is a very wide pair of mag. 4.5 and 9.8 white stars 58”
apart. The separation ensures that the glare of the primary
does not overwhelm the secondary. The latter is itself an equal
mag. 10.6 pair at 1.9” distance.
Mu Lib (14h 49.4m, -14° 09’) is
a mag. 5.8 very pale yellow component 1.9” away from a
white mag. 6.7 companion that was just split with 154x power.
Burnham 122 (15h 39.9m, -19° 46’)
is nestled in a starfield close to Kappa and 41 Librae. The
1.8”-wide double consists of pale yellow, equal (m. 7.6,
7.8) stars.
HN28 (14h 57.5m, --21° 25’): I
had great expectations for this one. John Herschell described
this couple as yellow and not a bad miniature of Alpha Centauri.
Hartung said they were orange and red. With mags. 5.8 and 7.9,
and a wide 23” separation, it’s easy for small apertures.
Larger apertures will show the colors better – a gourmet’s
delight. My verdict: I think Hartung was closer, although users
of small scopes will probably side with Herschell.
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CAS
Annual Dinner and CAS Awards
Nicole Kennedy
The
CAS Annual Dinner was held on the 19th June 2003, at the Yamba
Club, Woden. Amidst the usual fun, frivolity and idiocy that
abounds, a variety of CAS Awards were given out.
Albert Brakel and
Judy
Bobroff were finally given their 2002 plaques, Albert for his
dedicated Society service over many years, including as Editor and
writer for Southern Cross, Committee
member, ongoing Vice-President, RAPT member, lunar graze and asteroid
occultation observer, etc, etc, and Judy for her staunch meeting/deep
sky night/group night supportive presence.
Four special awards were also
presented on the night:
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Ross Gould for his services
as Editor of the Southern Cross Journal, writer for said Journal, ex-President of 3 years, and
ongoing Committee member.
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Pat Purcell, in recognition
of his brilliant Introductory sessions, past Committee work,
RAPT work, observing lunar grazes and 3 asteroidal occultations
(1994, 2002, 2003), as well as consistent and appreciated
showings for group/school nights and finally.
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John Howard, an ex-President,
for his continued efforts as ongoing Deep Sky Night Co-ordinator,
ongoing Public Contact for CAS, and ongoing Light Pollution
Officer.
The President of CAS,
Andrew
White, also presented a Patronage certificate to Dr Penny Sackett,
RSAA, formally acknowledging her as the Patron of CAS.
This year, the CAS entertainment
sub-committee bucked tradition (we were tired of Ross Gould
answering all the questions correctly!) and passed on the idea
of a Trivia Quiz. Instead, those at the Dinner were delighted
(or stunned) to be subjected to questions from the Venerable
Alien and his noisy sidekick. Vince Ford and Steve Kennedy managed
to enliven the crowd with really bizarre and little known questions
and answers. Prizes were awarded to each table with correct
if unimaginative answers (nice wine, but not a shade on the
cool Moon sticker book A. Brakel won!) and much noisy fun was
had by all.
The Yamba Club turned out three
superb courses, with choc and lollies on each table fuelling
us early on. Typical CAS, however: the lollies, in bags suspended
from helium balloons (and weren't they fun!) became part of
a Physics quiz. I think the table holding the CAS Social Reporter,
Treasurer, Co-Editor, Senior Vice President, guest CAS accountant
and others, was disqualified from the competition: something
about eating all the chocolates and inhaling the helium.
All in all, a tremendous night
was had. Everyone agreed the food was fabulous, the entertainment
fun, rowdy, exciting (kamikaze balloons and a challenge to the
Presidency, but as it was made under helium we all ignored it).
Above all, the company was congenial and convivial. It was an
opportunity for CAS to get together within an enjoyable social
occasion, have a bit of fun, meet our Patron and just enjoy
ourselves.
Thanks especially to Kim Rawlings,
Andrew White, and their littlehelpers, for their superb organising,
decorating and awards efforts. We hope to see you all there
next year! Clear skies!
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Circinus
and Triangulum Australe
Jenni Kay FRAS
Circinus and Triangulum Australe are neighbours deep in the
southern sky. Both are easy to pick out in the sky with the
principal stars ranging from about 1.9 mag. to 3.2 mag. While
these constellations are not overly rich in deep sky objects,
every one of them is worth the effort to seek out.
The following observations were made with a 12.5” f/5
Newtonian, from my semi-rural home site in Lobethal SA. The
skies typically offer a limiting naked eye magnitude of 6.1
and the seeing rated at ANT II-III.
I have also appended a few observations made at Riverton with
the 30” f/5 Newtonian. Here the sky offers a naked eye
magnitude of about 6.5, seeing ANT II-III.
Circinus
ESO 97-13 : 14 13 09 –65 20 18 Galaxy
(GX)
105X : requires averted vision, suspected as relatively faint,
relatively small, round, hazy spot, with a star at the western
edge. 150X: Much improved – relatively bright, small,
round, 30” in size, with a high surface brightness,
and a smooth glow throughout.
NGC 5288 : 13 48.7 –64 40 Open Star
Cluster (OC)
105X: Obvious enough, as a small collection of a few relatively
faint stars. The cluster stands out well in the general star
field where there are a good many brighter 10 -11 mag. stars,
and one very bright 8th mag. field star, 3.0’ to the
SW, shining in a marvellous golden yellow colour. 150X: Overall,
there are twenty stars involved, most are 12 mag., the cluster
is well concentrated, a little elongated SW – NE with
a size 2.5’ x 1.5’. The cluster leaves an impression
of being a fine, dainty sight in a rich star field.
NGC 5315 : 13 53.9 –66 31 Planetary
Nebula (PN)
105X: Obvious enough, as a very bright, very small, almost
stellar, hazy disc. 150X: Improved – very bright, round,
6.0” in size, and while being very small, the eye easily
notices this is a non-stellar object. There is a positive
response to the OIII filter.
NGC 5359 : 13 59.8 –70 24 (OC)
105X: Obvious, but more like an asterism rather than a cluster
per se. This is a large, loose group of stars, all similar
in brightness at 10-12 mag. Immediately around this group
there is a noticeable drop in field star numbers, almost as
if it is isolated from the rest of the rich star region. 150X:
There are some fifty stars involved, with an overall irregular
shape stretched a little NE – SW, and a size of 14.0’
long.
NGC 5715 : 14 43.4 –57 35 (OC)
105X: Obvious – not impressive as a star cluster as
it appears little more than a couple of long curling strings
of stars and is open in the central region. It is a small
group of stars, all similar in brightness at 11 mag., standing
out as a quaint sight in the general bright and rich surrounds.
150X: Similar view: twenty stars involved, somewhat concentrated
and 4.0’ in size.
NGC 5823 : 15 05.5 –55 37 (OC)
105X: Obvious, well detached, large, fairly rich, slightly
concentrated, all stars similar in brightness at 11-12 mag.
with a few fainter. The cluster lies in a rich star field
of 10-12 mag. and fainter stars which are evenly scattered.
150X: Impressive – large, 9.0’ in size, almost
spherical in overall shape. There is one long chain of stars
forming nearly a circlet, with a short row of stars bisecting
it. Other cluster stars lie in small rows and curving strings.
Overall, there are forty-five stars involved.
Triangulum Australe
IC 4585 : 16 00.2 –66 19 (GX)
105X: Too faint. 150X: Requires care and averted vision –
very faint, relatively small, elongated SW – NE, 1.0’
x 20” in size, with a low surface brightness.
NGC 5844 : 15 10.7 –64 41 (PN)
105X: Obvious — relatively faint, large, round hazy
glow. Positive response to the UHC filter. 150X: Impressive
– relatively bright, elongated E-W, 50” x 40”
in size, smooth glow throughout. There is a neat double star
(B 832) 3.0’ to the NE, an unequal pair of 9/11 mag.
showing colours of golden yellow + mauve, with a separation
of 4.8”.
NGC 5938 : 15 36.4 –66 51 (GX)
105X: Suspected – very faint, hazy glow. 150X: Improved
– obvious enough, very faint, small, round, hazy spot,
30” in size, with a low surface brightness.
NGC 5979 : 15 47.7 –61 13 (PN)
105X: Obvious – bright, small, round, disc, with soft
edges. There is a positive response to the UHC filter. 150X:
Improved – bright, round, 20” in size. The rest
of the field is fairly rich in 11 – 12 mag. stars and
a few brighter 10 mag.
NGC 6025 : 16 03 14 –60 24 21 (OC)
8x50mm finderscope : obvious, small grouping of relatively
bright stars. 105X: Dazzler – large, somewhat concentrated
group of bright stars, pretty rich, with a very irregular
overall shape. 150X: Splendid – there are forty-five
stars involved, ranging in brightness from 8 – 10 mag.
and a few fainter. The stars lie in long curving chains. Overall,
the cluster is 15.0’ in size. The view is quite outstanding
with these bright stars strewn across a dark, smooth, background
sky.
NGC 6156 : 16 34.9 –60 37 (GX)
105X: Shy, soft, faint, small, round hazy spot, a little lost
among a few stars. 150X: Improved – relatively faint,
round, 40” in size, showing a hint of structure and
some faint stars superimposed. The galaxy gradually brightens
towards the centre, and has a high surface brightness.
NGC 6183 : 16 41.7 –69 22 (GX)
105X: Obvious – faint, long and slim hazy wisp. 150X:
Improved – relatively faint, major axis lies SW –
NE, 45” x 10” in size, and gradually brightens
towards the centre. Overall, the galaxy has a high surface
brightness and shows a little mottling.
Riverton, SA. 30-inch f/5 Newt.
Triangulum Australe
ESO 137-3 : 16 13 48 –61 00 13 (GX)
360X: Obvious – relatively faint, small, round, hazy
spot, 25” in size. 1.0’ to the SE lies a second,
relatively faint, small, round, hazy spot, and this too is
about 25” in size. About 1.5’ to the NE lies a
third, small, relatively faint, round, fuzzy spot, 25”
in size. Some modern catalogues state there is one large galaxy
here, but the NED database at Caltech, which is constantly
being updated, notes the three galaxies here.
ESO 137-6 : 16 15 04 –60 54 26 (GX)
11.0’ NE of ESO 137-3. 360X: Very obvious – bright,
small, round, glow 30” in size, with the hint of a very
faint, outer halo taking the overall size out to 40”.
The galaxy has a high surface brightness and a smooth glow
throughout.
ESO 137-7 : 16 15 33 –60 39 54 (GX)
15.0’ NNE of E137-6. 240X: Obvious — relatively
faint, small, round, hazy glow, 30” in size.
ESO 137-8 : 16 15 46 –60 55 11 (GX)
15.5’ near S of E137-7. 360X: Very prominent –
bright, small, round, central core within a relatively large,
faint, halo 1.0’ in size.
ESO 137-10 : 16 15 50 –60 48 10 (GX)
7.0’ near N of E137-8. 360X: Obvious – relatively
bright, elongated NNW – SSE, 2.5’ long, with a
bright, round, core 40” in size.
ESO 137-11 : 16 15 53 –60 50 58 (GX)
3.0’ S of E137-10. 360X: Obvious enough with some care
and averted vision – faint, very small, almost stellar,
round, fuzzy spot.
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