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Southern Cross - April 2002
Western CarinaAlbert Brakel In April 2000 we looked at the obsolete constellation of Robur Carolinum, which occupied what we know as eastern Carina. This month's COTM looks at the rest of the constellation, and is in effect Carina part 2. Unlike the eastern half, which is rich in emission nebulae, planetary nebulae and open clusters, western Carina has only one cluster, a difficult small nebula, and double stars, despite lying in the Milky Way. However, the double stars include several outstanding ones. An impressive naked-eye jewel in the region is, of course, Canopus (RA 06h 24m, Dec.-52º 42'), the second-brightest star in the sky. Lying 313 light years away, it is 15,000 times as luminous as the Sun, has a diameter 65 times greater, and its magnetically-heated corona, 10 times hotter than the Sun's, produces both observable X-rays and radio waves. Not quite massive enough to explode, Canopus will eventually die as a massive neon-oxygen white dwarf. Three degrees NE of Canopus and one degree SW of Tau Puppis, close to the constellation border, is the Carina dwarf galaxy (06h 41.5m, -50 57'), one of many such dwarfs orbiting the Milky Way. The dwarfs are notoriously difficult to detect visually, and this particular one is impossible for amateurs, so low is its surface brightness. I throw it in as a challenge for the CCD brigade. But now it's time for some objects worth turning the telescope onto, and as we're at the western end of the constellation, we may as well work our way eastwards in RA from there. I used a 20 cm aperture. The binary Dunlop 39 (07h 03.3m, -59° 11') consists of mags. 5.9 and 6.9 components 1.6" apart. It took 235x before they were barely resolved, so that particular night was obviously not ideal. Rumker 6 (Dunlop 44) (07h 20.4m, -52° 19') is a lovely equant yellow pair, easily resolved, even with 50x. Their magnitudes are 6.0 and 6.0 at 8.9" separation. In the same field 8' NE is another attractive pair, h3958, that has a mag. 7.2 yellow primary lying a wide 30" from the mag. 9.0 ashen secondary, that is well within the capability of 50x. The two binaries, together with a mag. 5.4 pale yellow star 7' to the north, make a fine sight. NGC 2516 (07h 58.3m, -60° 52') represents the only open cluster in western Carina, and it's beautiful, with a range of star colors from orange to yellow, white, and bluish, and effective at low powers such as 77x. With a diameter of 30' and an integrated magnitude of 3.8, it is visible to the unaided eye as a misty patch. Even binoculars can resolve over a dozen of the 80 or so constituent stars. The brightest members (mag. 7) are orange stars on the NE, N and NW sides, and a white one on the SE. Enhancing the cluster further are a couple of easy multiple stars. h4031 lies in the southeast, and is a mag. 7.2 and 8.0 pair 5.5" apart, aligned N-S and easily split by 77x. In the WSW, h4027 is a triple system with mag. 8.8, 8.4 and 9.9 components lined up roughly E-W for 38", the brightest in the middle; the line is continued a further 20" or so west by a much fainter unrelated star. About 1½° north of the cluster is the irregular red variable V341 Car (mag. 6.2-7.1), but it is better known for the nebula that surrounds it, IC 2220 - the Toby Jug Nebula (07h 56.8m, -59° 07'). The nebulosity is not easy to detect - I couldn't see it with the C8 from my suburban backyard with any power. The bipolar reflection nebula shows on photos as a squarish area somewhat reminiscent of a jug. The central star could be an outlier of NGC 2516. c Carinae (Rumker 8) (08h 15.3m, -62° 55') is a grossly unequal pair (m5.3 and m7.8) of white and yellow stars. At a distance of 4.0", 77x was able to separate them, but they looked better with 154x. h4128 (08h 39.2m, -60° 19'), a close (1.2") white twosome, required 235x to be just resolved. Their magnitudes are 6.9 and 7.5. h4130 (08h 40.7m, -57° 33') is another example of an unequal binary, with mags. 6.5 and 8.4 spaced at 3.6". 77x sufficed to distinguish the white primary from the yellow companion, but 117x provided a better split. Rumker 9 (08h 45.1m, -58° 44'), an equal white mags. 6.9 and 7.0 pair at 4.1", could just be resolved with 50x, but more confidently with 77x. Nearby, the duplicity of b2 Car (08h 59.4m, -59° 05') was easily disclosed by 50x power, but not by hand-held binoculars. Galaxies are not a notable feature of this Milky Way region, although some faint ones are recorded on sky charts. The brightest one, or rather the least dim one, is NGC 2640 (8h 37m, -55º 07'), located about a degree WSW of Delta Velorum in the False Cross, close to the constellation border. It was not visible in my suburban sky. WebCam
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Albert Brakel
Last January, the Australian Government received a letter from the International Spaceguard Center, signed by 91 scientists from 18 countries, pleading for Australia to help with the search for near-Earth asteroids (NEAs) that could pose a risk to our planet (Southern Cross, Feb. 2002, p.9). The Northern Hemisphere-based search programs can only search down to about declination -40°, leaving us blind to anything approaching in the far southern sky. Most known near-Earth asteroids have been found from the Northern Hemisphere, so that the southern sky now holds the greatest potential for a surprise impactor.
What was asked for was a suitable search telescope facility in Australia costing several million dollars (much of which might be covered by contributions of equipment from the USA), and an operational cost of less than a million dollars per year. This would be a highly cost-effective investment in the prevention of the tremendous loss of life and economic damage that could result from an asteroid impact.
Last March the Government gave its answer: No. In a TV interview on 60 Minutes, Science Minister Peter McGauran described the request as "a fruitless, unnecessary, self-indulgent exercise". He went on to say that "a lot of worries keep me up at night, but asteroids are not among them. I'm not going to be spooked or panicked into spending scarce research dollars on a fruitless attempt to predict the next asteroid."
He then accused the signatories to the letter as being "scientific generalists", and said "I want astronomers themselves, under the supervision of an objective world-wide working party, making a true and proper assessment. I'm just not convinced that the hype and alarm and even fear-mongering is enough to justify an instant investment."
One wonders just where the minister is getting his advice from. The signatories to the letter include about as prominent a group of world experts on asteroids as you could hope to get. There was Brian Marsden, who runs the Central Bureau for Astronomical Telegrams, which alerts the world to closely-approaching asteroids. Gareth Williams, head of the Minor Planet Center. Tom Gehrels, an author of authoritative professional texts on asteroids. Caroline Shoemaker, who with her late husband discovered hundreds of asteroids and comets, including Comet Shoemaker-Levy 9 which crashed into Jupiter in fragments. David Levy, co-discoverer of that comet and many others. Eleanor Helin, head of the Near-Earth Asteroid Team (NEAT) program that has discovered dozens of NEAs and comets. Gerrit Verschuur, an astronomer who has written a book on the threat of impacting asteroids. Clark Chapman, an asteroid authority and a Principle Investigator on the NEAR-Shoemaker mission to the asteroid Eros. Lou Friedman, Executive Director of the Planetary Society which has long funded asteroid searches. And so on. Hardly a bunch of "scientific generalists". Minister, you have already heard from your "world-wide working party".
Part of the problem for politicians, and even scientists in other disciplines who have to compete for research funds, is that the probability of a damaging impact seems remote. Why spend scarce money on something that is unlikely to happen in our lifetime? If only we could be sure of that. That the danger of impacts is real is demonstrated by several occurrences in the 20th Century. In 1908, a small 50-metre asteroid hit an isolated area called Tunguska in Siberia and flattened 2000 square km of forest. Had it arrived a few hours later, it would have hit Europe and we would not now be so blasé about such impacts. In 1947 another body hit the Sikhote-Alin region 400 km from Vladivostok, forming craters. The western USA narrowly missed a 10-megaton impact in 1972 when an object was seen to skip off the atmosphere; had it approached at a steeper angle it would have devastated the area below. And we all know that as recently as July 1994 fragments of Comet Shoemaker-Levy 9, each no more than a few kilometres across, collided with the planet Jupiter and caused impact scars in its atmosphere larger than the Earth in size. These things have all happened in living memory, and will continue to happen. Let's hope the next Tunguska-type event, reckoned to occur about once a century, doesn't happen over southeastern Australia.
The Americans and Europeans have been less complacent. The US Congress has mandated NASA to find 90% of potentially dangerous asteroids larger than 1 km by 2008. But this target will not be reached unless a serious effort is also mounted in the Southern Hemisphere. In the process, many smaller but still dangerous asteroids will also be found. The concern in the North should translate into a significant part of the initial cost for a southern facility being met by overseas funding, leaving only a relatively small amount to be contributed by Australia.
It is important to realize that an object on a collision course that will reach Earth in a matter of days cannot be stopped. The goal is to find dangerous asteroids at least 30 years before they are due to arrive, so that there is time to give them a slight nudge at a critical point in their orbit, making them end up missing us. It will also enable us to study their make-up, so that we know what kind of nudge is best to give them.
But where will our Government get the money? Well frankly, a million dollars per year operating cost is peanuts these days. The multi-million-dollar New Year fireworks displays over Sydney Harbour cost more. If it's worth spending this much on a bit of entertainment, it's worth spending a smaller amount on asteroid insurance, considering the overwhelming consequences of an impact. Because that's what it is, insurance. Like any insurance policy, you hope that the event you insure against never happens. Your house has probably never burned down, and is very unlikely to burn down this year, but would you leave your house uninsured?
Jenni Kay FRAS
Back in 1995, Southern Sky magazine introduced readers to the Bennett Catalogue. When I first read it I thought that it would make for a most interesting observing project, but alas, I didn't do anything about it at the time. This year I have decided to undertake this very project. While at this time of the year I won't be able to begin with the first object in the catalogue, NGC 55 in Sculptor, I will have to settle for number 37, or Bennett 37 (Ben 37), and carry on from there. But first, here is a brief background on the Bennett Catalogue.
In the 1960s Jack Bennett, a well-respected member of the South African Astronomical Society, made observations with his 5-inch refractor from his urban backyard. He was a dedicated comet hunter, and compiled a list of 152 southern NGC objects that appear comet-like, in order to help others eliminate them in comet searches. He not only discovered two comets, but he also found a supernova in M83. In the catalogue he includes 46 galaxies, 24 open clusters, 70 globular clusters, 3 diffuse nebulae, and 9 planetary nebulae. For more interesting information, please see May/June 1995 Southern Sky.
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; with the seeing rated at ANT II-III.
NGC 2298 : 06 49.0 -36 00 GC
105X: Very obvious and charming view - bright, large, round, hazy glow that is almost granular, with four 12 mag. stars resolving past the cluster edge. These are possibly wide outliers. 150X: Takes magnification well, offering an even more splendid view - bright, round glow, 3.0' in diameter, with the flicker in averted vision from numerous stars briefly resolving across the glow.
NGC 2467 : 07 52.6 -26 23 OC
It is the nebula that stands out visually, with the associated star cluster appearing little more than a handful of stars shining through the nebula. 83X: very obvious, bright, round, relatively large, hazy glow, with a mag. 8 star a little north of centre and a few other faint stars involved. While this is an extensive, rich and bright star field, the eye is drawn to the nebula as soon as it moves into view. 150X: Bright neb, 5.0' in size, with a very strong response to the UHC filter. Apart from the mag. 8 star involved, there are a further nine 12th mag. stars within the nebula.
NGC 2489 : 07 56.2 -30 04 OC
83X: Stands out very well in the busy star field - relatively large, rich, strong concentration of bright 11 mag. stars. There are eighty stars involved in this 20' diameter cluster, with a strong central concentration and gradual thinning out towards the edges. 150X: Similar view. It is the whole view that is worth a mention. Apart from the cluster appearing as a gem in a busy star field, there are three bright field stars nearby displaying good colour. 13' south of the cluster lies a 6.3 mag. star showing a strong yellow colour, a yellow/white 4.3 dazzler lies southeast of the cluster, and a soft yellow 7.3 mag. star lies to the southwest. On the other side of this line of three stars lies the cluster Ha 20. All in all, a most remarkable field!
NGC 2506 : 08 12.0 -10 47 OC
The field is a short 5 degree star hop, ESE of Alpha Mon, which itself is a remarkable deep orange coloured star. 105X: Splendid view - very obvious, relatively large, soft glow with nine 12 mag. stars resolving well. Averted catches the flicker from numerous stars involved and near resolving. 150X: Improved - Averted vision shows a tight cluster of about one hundred stars, 12 mag. and fainter, in an overall spherical shape, with a diameter of 5', strong central concentration and well detached.
NGC 2627 : 08 37.3 -29 57 OC
In a field full of stars, this cluster stands out well at low power appearing as a rich condensation of relatively faint stars. The cluster is large, has an overall irregular shape and is well concentrated. At 150X the view is much more dramatic, as the very faint stars begin to resolve. There are forty-five stars involved, with a brightness range from 11-14 mag, and then fainter. In general, there are bright stars over faint stars and haze. The cluster is about 15' in size. The rest of the field is a mix of bright and faint stars, and with this cluster standing out so well the view is most attractive.
NGC 2671 : 08 46.2 -41 53 OC
Lies about 4.5 degrees NW of Lambda Vel, which is an attractive deep orange star. 105X: Obvious - relatively faint, soft, collection of a few stars in a rather small group. This delicate gem lies in a busy star field, but still stands out well. All the stars are similar in brightness at 12/13 mag, with a population of thirty stars. 150X: The cluster is 5' in diameter, shows some central concentration, with an overall spherical shape. An impressive soft and dainty sight!
NGC 2808 : 09 12.0 -64 52 GC
8x50mm finderscope : bright, small, round, hazy spot. 55X: Extremely bright, compact core, within a much extended, bright, round glow. The glow fades quickly to the edges from the thinning of outliers. 105/150X: Very impressive - bright, large glow, with a suddenly intensive core. Averted vision catches the flicker from numerous stars resolving, while with direct vision the glow displays a peppery effect from stars near resolving. The core region is about 35" in diameter, with the cluster edge to edge being 5' in size.
NGC 2972 : 09 40.3 -50 20 OC
105X: A little charmer - hardly resembles a cluster per se, as it is little more than a few long star chains, meeting in the middle in a knot of stars. Unusual, and attractive! 150X: There are thirty stars, all similar in brightness at 13 mag, with an overall size of 6.0' SE - NW x 2.5'. The cluster stands out well in the rich star field, surrounded by mostly somewhat faint stars with a couple of brighter ones.
NGC 2997 : 09 45.6 -31 11 GX
50X: Very obvious - bright, large, oval shaped, hazy glow. 105/150X: Improved view - bright, large, oval, 6' x 4' in size, major axis lies NW - SE, with a high surface brightness. There is a brighter, small round, central core, 20" in size. Nearby to the east lie six bright 7-9 mag. field stars shaping a prominent step pattern, that add extra appeal to the already impressive view with the bright galaxy.
NGC 3115 : 10 05.2 -07 43 GX
105X: WOW! Nice! - Very bright, relatively small, little elongated core, within a long, slim, bright halo. There is also a central bulge from a very bright, very small, nucleus. The galaxy is obvious and eye-catching. 150X: very impressive - relatively bright, long edge-on, 7.0' x 30", with an intense core 30" x 15", and a nucleus 20" in size. The major axis is NE - SW, and the galaxy has a high surface brightness.
NGC 3132 : 10 07.0 -40 26 PN "Eight Burst nebula"
105X: Remarkable - bright, relatively small, round disc, with a very bright, 10 mag. central star. There is a strong response to the UHC filter. The planetary lies in a rich star field and the whole view is striking. 150X: More interesting - the central region is darker, with a brighter ring around the outer edge of the disc that is stronger on the western side. Overall, the planetary is very bright, round, and 50" in size.
NGC 3201 : 10 17.6 -46 25 GC
105X: Superb - large, classic type globular cluster with stars resolved from the edge to the core over a bright, large, round background glow. The stars resolved are all similar in brightness at 13 mag. 150X: magnificent - large, bright, round glow, with at least eighty stars resolved well, and more with averted vision. The cluster is 8.0' in diameter.
NGC 3242 : 10 24.8 -18 38
105X: Incredible - very bright, relatively small, round, sky-blue coloured hazy glow, or slightly squashed into a football shape. The planetary shows a bright and even glow throughout, with a soft, diffuse edge, and the central 12 mag. stars seen. There is a strong response to the OIIII filter. 150X: More interesting - the football shape seems to be enwrapped in multiple soft, layered shells. The planetary is 25" in size.
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