Polar Discovery

"…Glide on in your beauty, ye youthful spheres,

To weave the dance that measures the years;

Glide on, in the glory and gladness sent,

To the farthest wall of the firmament, --

The boundless visible smile of Him,

To the veil of whose brow your lamps are dim..."

~Song of the Stars - William Cullen Bryant, 1832

Immediately around the south polar region of the sky lie a number of obscure and often overlooked constellations, some admittedly deprived of the outstanding celestial jewels that bedeck the wealthier constellations. However, even here, there is a scattering of worthwhile objects and occasionally a heavenly surprise awaiting the avid sky watcher. Names like Apus, Pavo and the unromantic Triangulum Australe are well placed in the winter evening sky. Here we will start our journey of discovery. John Dryden’s Ode to Doctor Charleton claimed,

“And all the stars that shine in southern skies

Had been admired by none but savage eyes.”

Johann Bayer adopted the above three groupings into his Uranometria of 1603, the first star atlas to encompass the entire sky including new constellations adapted from the discoveries of two Dutch navigators, Pieter Keyser and Frederick de Houtman. The astronomer and cartographer Petrus Plancius asked the pair to fill in the uncharted skies around the South Celestial pole while on their journey to the East Indies in 1595. Upon their return two years later, twelve new constellations were delivered to Plancius who incorporated them on to his globe along with a number of other constellations. Only three of Pancius’s constellations survive; Camelopardalis the 'Giraffe' in the northern sky and the southern Columba the 'Dove' and Monoceros the 'Unicorn'.

Apus the 'Bird of Paradise' lies directly south of 'The Pointers' alpha and beta Centauri, its southern boundary meeting the unpretentious Octans. Apus is the French Oiseau de Paradis, the German Paradies Vogel and the Italian Uccello Paradiso. The Chinese revered it as E Cho the 'Curious Sparrow' as well as the 'Little Wonder Bird'. Apus is derived from apous 'without feet', representing the legless swallow of ancient Greek mythology.

The brightest star alpha, an orange giant of magnitude 3.8, marginally outshines gamma. The later star is yellow in colour, as is nearby beta and their respective magnitudes are 3.9 and 4.2. Delta¹ and delta² are a delightful binocular double of giant orange suns of magnitudes 4.7 and 5.3.

I 236 is a lovely double system composed of a magnitude 5.8 yellow star with a magnitude 8.0 companion lying close. A slowly widening separation of 2”.0 was measured in 1947. Another double star worth pursuing is Cap0 15, a very close pair of magnitude 7.5 and 9.0 suns. However, because of the fainter magnitudes involved here, glare is kept to a minimum and a smaller aperture can resolve this system on a good night.

There are two globular clusters available to the observer in Apus. IC 4499 was discovered photographically, missed by astronomical giants such as John Herschel. This is one for larger apertures as a 20cm aperture struggles with it. Look for a faint roundish glow 3’ in diameter set within a faint stellar backdrop in the southern reaches of Apus. The other ball of suns is NGC 6101 in the north, packed full of faint stars, many trailing out from the brighter central region as rays. A leap northwards crosses into our next constellation, Triangulum Australe.

Triangulum Australe, the 'Southern Triangle', lies south of Norma and separated from 'The Pointers' by narrow Circinus. This easily found triangle (sides 8° x 8° x 6.5°), composed of the bright stars alpha, beta and gamma were the 'Three Patriarchs', ostensibly the biblical Abraham, Jacob and Isaac. Alpha is a magnitude 1.9 orange giant star 80 light years distant with beta, a magnitude 2.9 white sun closer to our Sun at 40 light years. Magnitude 2.9 gamma is a curious blue-white star strong in spectral lines of the rare element Europium, an element and lying a little further away at 115 light years.

There is one open cluster and a nice planetary nebula as well as many faint galaxies scattered throughout the 'Triangle'. Many double stars inhabit this area. I 332 is a close pair of magnitude 6.5 and 8.5 stars, the primary of a yellowish hue. A 20cm aperture separates them on a steady night immersed within a field peppered with stars.

Rmk 20 is another fine pair, this time of equal magnitudes 6.3 and separated by less than 2”.0. Both are yellowish A-type stars resolved in a 20cm, the orbit rather long and the separation very slowly closing since discovery. The surrounding field is busy with stars, interspersed with many dark areas of dust and gas.

Slr 11 is a particularly fine multiple system with the bright yellow star of magnitude 6.5 almost overwhelming its close magnitude 8.8 companion. Two further stars are listed in Sky catalogue 2000 as members though Hartung suggests they may be field stars. Both stars are within the grasp of small apertures, their magnitudes glowing at 9.1 and 8.7.

Iota is an unequal pair of magnitudes 5.3 and 10.3, discovered by J Dunlop in 1826. The yellow primary is reflected by its spectral type, F3 or F4 and is also a spectroscopic binary. The period of this hidden companion, determined in the 1920’s, is 39.888 days with a mean separation of some 20 million kilometres.

NGC 5979 is a pale disk lying within a star studded field northwest of beta. A planetary nebula, even small apertures will separate it from the background stars. A planetary nebula is the signature of a dying star, 'gently' puffing away its atmosphere to settle down as a white dwarf, something our Sun is expected to do in the next 5 billion years or so.

NGC 6025 is a lovely open cluster of bright yellow and white stars half the diameter of the Moon. Loosely constructed curves and lines of stars radiate outward.

Pavo lies south of Sagittarius and Corona Australis, separated by obscure Telescopium. Another of the celestial birds honoured in this region including Tucana (Toucan), Grus (Crane) and Phoenix, the delightful Pavo symbolises the beautiful peacock. Mythology associates the peacock with the Roman Goddess Juno from whose breast the Milky Way flowed.

There are many interpretations when it comes to mythology so I will go with the one I personally like. Juno suspected her husband Jupiter of, to put it politely, being flirtacious with Io, one of his many 'admirers'. Juno transformed Io into a white heifer, watched over by Argus, a creature with a hundred eyes. Jupiter, not to be out manoeuvred by his wife’s jealous temperament, prevailed upon Mercury to decapitate Argus and release the captive Io. Juno, not to be outdone by her husband’s deceit, placed the 100 eyes of Argus onto the peacock’s tail.

Pavo’s brightest luminary is magnitude 1.9 alpha on its northern edge. Known as the 'Peacock Star', studies have shown it to be a spectroscopic binary. Beta is a white A-type star of magnitude 3.4 and both delta and eta hold no claim to fame at magnitudes 3.6. Far more exciting is kappa Pavonis, one of the brightest Cepheid variable stars in the sky, classified as a W Virginis type. A yellow supergiant, it varies between magnitudes 3.9 to 4.8 every 9.1 days.

Xi Pavonis is an orange giant of magnitude 4.4 with a magnitude 8.6 white companion huddled close and needing high power to pull it away from the glare of the primary. This fainter white star may appear greenish in colour because of contrast with the brighter orange primary. Xi Pavonis dominates the surrounding field, its brilliance and colour overwhelming its lesser endowed neighbours.

A nice triple system is h5231, composed of magnitudes 8.1 and 8.7 stars separated by a reasonable 7”.0. The fainter star also has a companion of magnitude 9.2 but at 1”.0 separation, it needs a steady night and at least a 20cm telescope to separate them. The primary star of this system is also a variable named KZ Pavonis, an Algol-type eclipsing binary, fluctuating between magnitude 7.8 and 8.4 every 0.95 days.

Lying away from the plane of our Galaxy, Pavo is lacking in the open clusters that frequent the spiral arms. Whilst many of the objects held within the peacock’s realm are rather faint and mostly extra-galactic in nature, it does proudly proclaim one of the best globular clusters in the heavens, namely NGC 6752. The photographically stunning galaxy NGC 6744 is also resident here.

NGC 6752 is a beautiful ball of suns, the best object in Pavo. A 15cm aperture resolves the outer region into faint stars, larger apertures reveal a small core of easily resolved stars overlaid by a peppering of brighter stars, some curving out from the centre. There is a bright foreground star south of centre that appears double. NGC 6752 was probably first noticed by J. Dunlop in 1828, the third largest globular in the sky behind omega Centauri and 47 Tucanae. Hartung calls it:

“One of the gems of the sky. On a clear dark night this is a most lovely object; it is a moderately condensed type of globular cluster…the unusually bright outliers extending over 15’, involving an elegant pair (7.7 9.3 3”.0 238°). Many of the brighter stars…are in curved and looped arms, and look distinctly reddish.”

Galaxies are gregarious in nature, woven together with invisible strands of gravitational silk upon a background of celestial velvet. These groupings make observing a lot more exciting, Pavo holding one such chain of faint galaxies within its borders; NGC 6769, 6770, 6771 and the slightly brighter IC 4842. The largest, NGC 6769, lies 2° southeast of NGC 6752, a faint and round barred spiral galaxy with a slightly brighter nuclear region. Discovered by Sir John Herschel during his stay at the Cape of Good Hope with his 18-inch f/13 telescope. He recorded it as:

“vF, R, lbM, 20 arcseconds, The first of 3.”

A faint supernova 1997de was detected photographically at magnitude 17.5 on 28th August 1997.

NGC 6770 is another of Herschel’s discoveries, recorded as:

“eF, 15 arcseconds, The 2nd of 3.”

NGC 6771 is another difficult galaxy, needing a large aperture to spot. IC 4842 lies in the same field as the above three galaxies, faint and elongated with a brighter middle region.

Around 3° north of NGC 6752 is the spiral galaxy NGC 6753. A 20cm aperture will show a faint oval of light with a much brighter nucleus. Allan Sandage recorded this galaxy is a member of the NGC 6769 Group.

NGC 6744 is a large and stunning face-on barred spiral galaxy photographically, the bright nucleus elongated and many spiral arms curled about within a cocoon of fainter gas and unresolved stars. In a 20cm aperture, it is rather less impressive, the central bar obvious but the surrounding glow is of a low surface brightness. A low power with its resultant wide field is needed here to not only hold this large galaxy but to also provide contrast with the background sky. A 10cm aperture will show a bright oval central region surrounded by a fainter envelope. Larger apertures in the range of 25cm plus on a dark night may show a little spiral structure in the halo as well as many HII regions of gas. The current accepted distance to this Milky Way-like galaxy is 25 million light years.

NGC 6684 is a large and round galaxy of reasonable surface brightness with a bright almost stellar nuclear region, lying near 5 stars of the 6th and 7th magnitude. Yellowish theta Pavonis interferes with this galaxy, lying only 6’ to the northwest. Employ high power to remove theta from the field thereby removing much of the overwhelming glare.

NGC 6776 is an elliptical galaxy that shows little in amateur telescopes, its central region slightly brighter and appearing to the eye as an unresolved globular cluster.

Near sigma Pavonis lie two barred spiral galaxies, NGC 6943 and IC 5052. Northwest is NGC 6943, showing a large faint halo with a brighter central area. Southeast of sigma is IC 5052, a nice example of an edge-on galaxy, faint but not difficult to spot as a long thin even streak of light immersed within a pretty background of faint stars.

Many more objects including double stars and faint galaxies inhabit these three constellations, awaiting the patient and enthusiastic observer.

Clear skies and good hunting.