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CitationMoir, J. (1924) "How to find the famous telescopic objects of the South". Journal of the Astron. Soc. Southern Africa, Vol. 1, p. 109.
BibCode1924JASSA...1..109M
DescriptionJournal article

 

How To Find The Famous Telescopic Objects Of The South

By James Moir, D.Sc., M.A., F.I.C., etc. etc.

[page 109]

This paper is written because the author believes that many amateur observers are unable to find certain well-known objects in the heavens, and because practically all the books, which have popularised astronomy, are written for the Northern Hemisphere.

The following descriptions are intended to be used along with A.W. Long's maps (obtainable locally for a few shillings) for the time of observation. If the map is not used, the amateur – if "green" enough – may start looking for an object, which is not above the horizon at the time:

(1)   Omega Centauri, the large spherical cluster, lies at a distance of 13 degrees from the top star of the Cross (Gamma Crucis), and at an angle of 135° to the axis of the Cross, as the Pointers are, i.e., in the direction of Libra. The height of the Cross (Alpha to Gamma) is 6 degrees, a measurement which can be used all over the heavens in finder other objects.

Omega Centauri contains nearly ten thousand nearly equal stars, of which perhaps 10 percent can be seen in a 4-inch telescope, the rest forming a nebulous background like a tailless comet. The cluster is as large as the moon, but only a quarter of it is bright.

(2)   Xi Toucani (also called 47 Toucani) is a similar object: it is smaller (half the size of the moon). And with centre relatively much brighter than the outside. If the sky is clear enough for the smaller Magellanic Cloud to be picked up, the object is found at 1 degree from the Cloud in the direction of Grus.

If the sky is hazy, imagine a line from Achernar to Alpha Trianguli, when Xi Toucani will lie on this line one-third of the way from Achernar. Achernar is the bright star lying on the opposite side of the pole from the Cross-Pointers. Alpha Trianguli is the yellow star opposite to the brighter of the two Pointers in a striking diamond shaped figure.

Both of these clusters are conspicuous in a field glass as round, hazy objects a quarter the size of the moon in the field glass.

The individual stars in Xi Toucani are entirely beyond the power of an amateur's telescope; there are about 9,000 of them.]

(3)   M 2 Aquarii. This is a third globular cluster, and being 1 degree South of the Equator, just comes within our purview. The cluster is 5 degrees north of Beta

[page 110]

Aquarii, i.e., on the line between the Dolphin and Pegasus, Beta Aquarii is the nearest bright star due north of the lozenge-shaped end of Capricornus, and is half-way between Fomalhaut and the Dolphin. This ball of stars is of looser texture than the others.

(4)   The Keyhole Nebula. This is the bright spot in the Milky Way near the Cross (about as far off on one side and curving tot he south as the Pointers are on the other). It is sometimes marked as Eta Argus on the maps, and lies roughly on the line joining Canopus to the boundary of Virgo and Libra.

Even a field glass shows the black chasm or keyhole between the two nebulae, and quite a small telescope shows an extraordinary frog-spawn effect caused by equal small stars lying on a nebulous background. This background is gas rendered luminous by electrical discharges.

The whole neighbourhood is a "glorious and innumerable procession of starts," to quote Herschel junior.

(5)   The Looped Nebula (30 Doradus). This occupies a position relative to the larger Magellanic Cloud similar to the position of Xi Toucani relative to the smaller Magellanic Cloud, i.e., lying near in the direction of Argo, and as the larger Could is visible even in moonlight, no other directions for finding 30 Doradus are necessary. It requires a large telescope to see it adequately, when it appears as a lace-work of superimposed figures of eight, in a way even more remarkable than the Orion Nebula, although much fainter.

(6)   The Trifid Nebula (M. 20 Sagittarii). This is the middle object of a luminous patch, which really consists of two clusters and the nebula. It is 6 degrees due North of Gamma Sagittarii, one-third of the way from the triple group at the end of Sagittarius and Antares, and one third of the way between Antares and the middle of Capricornus. The word "trifid" means that it is split into three parts by three winding dark lanes meeting in the centre, something like the three-legged symbol of the Isle of Man. The other two adjacent objects are striking star-clusters.

(7)   The Omega Nebula (M 17 Sagittarii). This object, which resembles a horseshoe, requires a fairly good telescope. It lies at the edge of a small round bright patch of the Milky Way, halfway between Antares and Epsilon Aquilae, the latter being the tail star of the Eagle in line with the three stars forming its body (with Altair in middle). It is also halfway between the well-known pair in Serpens and the south near edge of Capricornus.

(8)   Planetary Nebula H. 27-4 Hydrae. This is a fairly bright blue oval nebula, like a faint imitation of Jupiter. It is 2 degrees south of Mu Hydrae, which itself is the second

[page 111]

Conspicuous star from Alpha Hydrae away from the head of Hydra. A line from the head of Hydra to the quadrilateral of Corvus has the nebula near its middle

(9)   Faint Spiral nebula in Aquarius N.G.C. 7293. This is included for completeness though much inferior to the Great Nebula of Andromeda. It lies one third of the way from Fomalhaut to Alpha Aquarii, 6 degrees from the nearest start in the "water-drops" of Aquarius. It is about the size of the moon, but very faint.

(10)   The triangular star-cluster Kappa Crucis. This is near the second brightest star of the Cross-, Beta Crucis. The cluster appears of the 4th or 5th magnitude, and lies towards the Coalsack in the continuation of the line joining the top of the Cross-to Beta, about 1-degree from the latter. The cluster looks like a sextant or like Euclid's figure for the Pons Asinorum, with one of the central stars conspicuously red.

(11)   The brilliant scattered cluster M7 Scorpionis. This is visible as a hazy spot between the end of the tail of Scorpio, and the adjacent bright stars of Sagittarius. It is about 1 degree in size and about 5 degrees measured at right angles from the last three stars of the tail of Scorpio. Some 20 stars are conspicuous, with many smaller ones.

(12)   The scattered cluster M6. This is 4 degrees north-west of M7, and makes an isosceles triangle with the Scorpion's sting and M7.

(13)   The large faint cluster near Sirius. This is 4 degrees due south of Sirius, i.e., roughly towards Canopus. Over 100 stars are visible, but only 5 are bright.

(14)   The Clusters near the "False Cross. " The first is about 6 degrees from the Keyhole Nebula (no.4 in this paper) in the direction of the greater Magellanic Cloud. The rest are Omicron Velorum, Pi Puppis, Epsilon and Theta, and X Carinae, all striking.

(15)   The Cluster in Scorpio N.G.C. 6231. At the place where Scorpio makes a sharp bend of 120 degrees is the star Zeta Scorpionis (really a naked-eye pair). The hazy place just north of this is the cluster, which contains 150 stars within the range of a four-inch telescope.

(16)   Double Stars. – Alpha Centauri is the best double star of the whole heavens. It is the brighter of the two. Pointers, and can be split into tow by a good binocular (if held steady). Alpha Crucis is the star at the foot of the Cross-, and consists of a close, very bright pair with a fainter third star at right angles some distance off - a striking combination. Rigel is the very bright white star at the top (south) side of Orion. It has a small blue companion visible in a 3 - inch telescope Sigma Orionus is 1 degree

[page 112]

from Orion's belt at one side and is a very complex star, two in very small telescopes, and then in very large ones, Sigma Scorpionis, the small star next to Antares, is a beautiful white and blue pair. Antares itself has a close green companion, which (owing to the glare) requires a 5- or 6-inch glass to reveal it. Sirius has a fairly bright violet companion, but an 8-inch glass is required to show it, again owing to glare. Beta Piscis Australis, of which the companion is reddish, is the second star from Fomalhaut 7 degrees off towards the long end of Grus. Beta Caprocorni, close to Alpha (a pair visible as a double star without optical aid) is a coloured pair, blue and yellow. Theta Eridani is a striking equal pair, and easy for any telescope. It is a bright star, the fourth from Achernar at a distance of 20 degree, and making a rough isosceles triangle with Canopus and Achernar, Theta being northerly to these two. Nu Scorpionis is a double double of the same kind as Epsilon Lyrae of the Northern Hemisphere: a low power shows it as two and each of the two splits into a pair with higher magnification. This star is a few degrees following Beta. Beta and Xi Scorpionis are both remarkable doubles: the former is the northern claw of the Scorpion, about 8 degrees from Antares in the direction of Arcturus; the latter is faint, about 8 degrees due north of Beta on a line passing between the well known pairs of stars in Serpens. Both of them are doubles with a third faint star. Gamma Crucis, the deep orange star forming the head of the Cross, has a distant but easily seen blue companion. Gamma Leporis has a red companion (which is rare) and another faint one: it is on the prolongation of the line joining Rigel of Orion to Alpha Leporis, the brightest star South of Orion (about 10 degrees from Rigel), and lies about 5 degrees from Alpha Leporis.

Beta Crucis does not require any finding. Delta Corvi is a distant yellow and blue pair: it is the one of the quadrilateral of Corvus nearest to Spica. 32 Eridani is a similar coloured pair, also known as Omcya Eridani. It is rather difficult to find. It lies on the line joining Sirius, Rigel and 10 degrees due north of Gamma Eridani. Others not requiring descriptions (being easily found) are Gamma Virginis, Alpha Piscium, Gamma Leonis, and Gamma Ceti, all striking close doubles.

Telescope tests, Iota Leonis, Zeta Aquarii, Pi Aquilae, Zeta Cancri, Tau Ophiuchi, and Epsilon Arietis are bright but very close doubles. For faint but not very close companions, in addition to Antares, there are Delta and Lambda Geminorum.

end

Digitization

Document type: Journal article.

Document source: Private collection, A. Slotegraaf

Scope: Complete article.

Scanning: A. Slotegraaf

Keyed in: M. Streicher

Proof reading: not done yet.

Online version: 2007 August 14, updated 2008 November 02.

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