Constellation of the Month - Octans

Albert Brakel

Octans the Octant is a constellation much beloved of editors of this journal, because it occupies the south celestial pole region, always staying in the same spot in the sky, and therefore can be slotted in as a COTM any month of the year. It does, however, have a northerly projection which culminates between August and October in early evening.

Owners of equatorial mounts may have difficulty observing close to the pole, but there is a simple remedy for non-permanently mounted instruments - don't align your telescope with the pole. The stars in this area move so slowly that alignment for visual observation is hardly needed anyway. As all directions from the pole are north, I'll have to indicate directions at times as below, left or right of the pole, which will be true enough for early evening at this time of year, but will of course vary with the time of night and the month.

The constellation was formed by Lacaille in1752, just 22 years after this navigational instrument was invented. Although superseded by the more accurate sextant in 1758, the octant continued to be used until the turn of this century.

Curiously, its brightest star is the 3.8 mag. Nu Octantis, followed by Beta, Delta, Gamma, and then 5.2 mag. Alpha. From this you might suspect that Octans is an extension of the "barren wasteland" of Chamaeleon and Mensa (as I once described them), but it does have some redeeming features.

Probably the only star most people remember seeing in Octans is the southern pole star, Sigma Octantis (21h 09m, -88 57'), which has a high rate of change of RA because of precession. There are various ways of finding Sigma, but at this time of year a method I find useful is to start at the Southern Cross, move down to the stars of Musca, extrapolate from Delta and Iota Mus to Alpha Aps, which lies at the northern end of a 5-degree-long south-trending arc of stars ending in Delta Oct. Another 5 degrees or so along the Alpha Aps - Delta Oct line beyond Delta brings you to a bit right of the pole. Moving a bit left with binoculars brings Sigma and Chi Oct into the field of view. Sigma is an undistinguished very pale yellow (F0) mag. 5.8 star. The South Celestial Pole (00h 00m, -90 00') lies close to a short arc of 7th and 8th mag. stars to the right of Sigma.

With binoculars still in hand, you should be able to find the open cluster Melotte 227 (20h 12m, -79 19) about one field diameter from Nu Oct. A low-power telescope showed a loose sprinking of about 3 dozen stars, including about a dozen reasonably bright ones, covering almost a degree of sky.

Some 4 degrees north of the cluster is Mu-2 Oct (20h 41.7m, -75 21'), a pretty 6.5 and 7.2 mag. yellow pair, and easy to resolve with small 'scopes because the separation is a wide 16.4".

Lamda Oct (21h 51m, -82 43'), a binary about 40% of the way between Nu Oct and the pole, is yellow and white, mags. 5.5 and 7.3, and not too difficult at 2.8".

Three other binaries lie in a band 4-5 deg. from the pole. Taking these in anticlockwise order, the first is Russell 38 (3h 43m, -85 16') lying below the pole. The yellow and white stars are mags. 6.7 and 8.2, and 2.2" apart.

The next two are some more small 'scope specials, so widely separated that x50 could split them with no trouble at all. Dunlop 82 (9h 33m, -86 01'), near Zeta, is an easy 15.7 " twosome of mag. 7.4 and 8.0 pale yellow and white stars, while h4490 (12h 02m, -85 38') is noteworthy for an orange-yellow 6.1 mag. primary with the ashen secondary a long 25" away, but fairly faint at mag. 10.4.

Octans is not famous for galaxies, and although it contains several, they are all somewhat of a challenge. With the ghastly weather we've been having the last few weeks, plus a Full Moon, I didn't get a chance to try any in time for this article. The brightest example is the NGC 6438 and 6438A galaxy pair (18h 26m, -85 25'), but at mag. 12.5 they would not be what you'd call blindingly bright. For the "big bucket" brigade, there is NGC 2573 (1h 42m, -89 20'), less than a degree from the pole and called "Nebula Polarissima Australis" by John Herschell. Hartung was unable to find it, but it really does exist and can be seen on a photo in the second edition of his book by Malin and Frew.

So that's Octans: not exactly a stunner of a constellation, but I hope you enjoy exploring it anyway.

The NGC/IC Project - Why Bother?

Robert E. Erdmann, Jr.
(Core Team Member & Project's Webmaster)

Introduction

The NGC/IC Project is yet another attempt at removing the errors from the NGC & IC Catalogues. One of the reasons is that it is still used as a source of names, and another reason is that many of the people involved in the discovery and observation of the nebulae were among the most famous astronomers of their day, and therefore, when there are known errors it equates to misattributing discoveries, or failures, to the wrong observer.

Most of the brighter, larger, nearer, and therefore most interesting non-stellar celestial objects are listed in the NGC and IC's. It has become an astronomical tradition to refer to objects by their NGC or IC numbers. Therefore, it makes sense to be sure that the number used to refer to an object does indeed belong to that object.

If the historical record is not correct, we run the risk of misattributing discoveries, and even making mistakes about the progress of astronomy itself. This evolves finally into a simple matter of historical truth. The NGC is a window on the world of the 19th century astronomer, but in its present form, it distorts our vision of our predecessors and of their accomplishments. In short, it warps history, and because astronomy is a science, and science is the ultimate quest for pure truth, it gives us a warped view of the truth.

There are at least a thousand known or potential identification problems in the NGC itself, and that many again (perhaps even more) in the IC's. This is an unfortunately large percentage of the total number of objects in each catalogue (7840 in the NGC, 5386 in the two IC's). These problems include, but are not limited to, poorly measured or simply wrong positions, confusion of one nebula for another, poor or missing descriptions, and so forth.

J. L. E. Dreyer -- Building the NGC and IC's

John Louis Emil (J. L. E.) Dreyer was born in Denmark, but emigrated to Ireland in 1874. He initially took a position to work at Lord Rosse's great observatory in Parsonstown (Birr Castle). Though Lord Rosse was an amateur, the third Earl of Rosse had built successively larger speculum (metal) mirror reflecting (Newtonian) telescopes through the late 1830's and early 1840's. The series culminated in a massive 72-inch diameter telescope, the largest in the world from the date of its completion in 1845 until its dismantling just before the first World War! Rosse, his son (the fourth earl), and his observers (Dreyer was one of these) spent years examining and measuring the known nebulae in the northern sky with the famous "Leviathan of Parsonstown," and discovered many more fainter nebulae themselves. A feat unto itself.

During the observations, it became clear to Dreyer that it was time to update Sir John Herschel's so-called "General Catalogue" of nebulae and star clusters, published in 1864. Just a decade later, there were simply too many new nebulae being discovered and too many different lists to consult for previous discoveries. Preparing observing lists or, simply finding if a nebula had been previously found by another observer, had become a time-consuming chore. Thus, Dreyer published a supplement to the GC of about 1000 new objects in 1878, and -- having suggested yet another supplement in 1886 -- was instead asked by the Royal Astronomical Society to assemble a "new general catalogue" of non-stellar objects. So, Dreyer added the latest 1500 objects to the previous lists, combined them all in Right Ascension (for 1860) order, and the "New General Catalogue of Nebulae and Star Clusters" appeared as Volume 49, Number 1 of the Memoirs of the RAS in 1888.

At the time, this was the most complete compilation of deep sky objects in existence, and was immediately adopted by professional astronomers around the world as the "ultimate" source of information about the non-stellar objects in the night sky.

It also must be remembered that Dreyer had to contend with an enormous amount of data and information without the aid of computers or any other labour saving cataloguing device. Assembling the NGC, Dreyer had to contend with conflicting claims of position and description for what he often suspected to be the same nebula. Some of these he could check himself; most, because of the overwhelming numbers of objects, he simply had to accept as published. Fortunately, he was an excellent transcriber, as very few of the errors in the NGC can be traced to carelessness on his part (his most common error, or that of his uncredited assistants, was to apply precession with the wrong sign to declinations). Most of the problems in the NGC are with the original positions and descriptions, coming as they did from many different observers using telescopes ranging in size from 2 inches to 72 inches, and relying on instrumentation that ranged from nonexistent to state of the art.

The Solution - Look at the Historical Record

There have been a number of major attempts at cleaning the NGC and IC's, including the RNGC and NGC 2000. Both of these failed, and may have even added to the confusion of mis-identified objects, primarily because they both ignored the historical record. As it turns out, the published papers of the contributing astronomers to Dreyer's NGC effort hold the key to really being able to scrub the NGC and IC's with impunity (in most cases). Dr. Harold G. Corwin, Jr., the Project's organizer, has been collecting the published papers of all of the contributors to the NGC throughout his career as a world class galaxy expert. It was his vision that the NGC and IC's be cleaned once and for all such that the objects in the NGC and IC's were as properly identified as was possible.

Having the papers of the original discoverers of the objects which made their way into the NGC and IC's has given the project an incredible advantage over past efforts. Because of this, the Project is well on its way to solving some of the most enigmatic puzzles in the NGC and IC's once and for all.