CONSTELLATIONS OF THE MONTH - Fornax

Steve Crouch

Given that its brightest star is only magnitude 4, Fornax could hardly be called a conspicuous constellation. It makes up for this, however, by having one of the best collections of galaxies in the sky, with one of my principal deep sky references indicating something like 275 of magnitude 15 or brighter. Most of the brighter ones are concentrated in the Fornax galaxy cluster which is easily found on the Fornax-Eridanus border just to the east of a prominent triangle of 4th magnitude stars, f, g and h Eridani. Included in the galaxies is the Fornax dwarf galaxy, the only one of these local group objects known to possess globular clusters, one of which can be viewed in 15cm. Fornax also has a bright planetary nebula and some interesting double stars, which, as usual, come first.

Because of the rarity of clear skies lately I decided to amalgamate the Fornax observations I did the last time it was constellation of the month (using a 28 cm C11) with the few opportunities that I have had to observe this time. The current observations were done with the 36 cm C14 and a 31 mm Nagler for the most part.

Double Stars
The first of these, B 663 (02 04.7, -33 05) is quite easy although not too bright (8.8, 12.0, 4.9" separation). Both components appeared white although my ability at judging double star colours is not all that good. Omega For ( 02 33.8, Dec. -28 14) is a similar double (5.0, 7.9, 10") with a much brighter primary. Alpha For (03 12.1, -28 59) is another unequal pair and quite an impressive object (4.0, 7.0, 4.2"). Fornax seems to have a lot of unequal doubles because the next one, HJ 3532 (02 48.6, -37 24) is one too. The magnitudes are 7.0 and 8.2 and the separation is 5.4". Yet another unequal pair is HJ 3536 (02 50.2, -35 50). The 5.8 magnitude primary has a magnitude 10 secondary at a separation of 10", which means it is more difficult than the others, but resolution was still easy in the 31 mm Nagler.

The final double I tried was B 679 (02 55.9, -38 38), which is rather more difficult (7.1, 12.0, 2.2"). This was more of a struggle, but I managed it with a 12 mm eyepiece.

In general, most of these doubles (except for the last) should be pretty easy in relatively small apertures.

Planetary Nebula
Fornax has only one planetary, which is not all that surprising given its distance from the galactic plane. NGC 1360 (03 33.3, -25 51) is a fairly bright object that is visible in a large finder scope under a dark sky. The C11 showed it as a large bright oval haze elongated NE-SW with a prominent central star. An OIII filter brightens the nebulosity but does not increase its overall extent. Reasonably deep images of NGC 1360 (including one I took myself) show a small reddish streak at the southern end which is presumably a jet from the central star. I don't know if this can be seen visually.

Galaxies
As stated before, Fornax has far too many galaxies for a column such as this to give a comprehensive treatment so I will confine myself to identifying the highlights and throw in one or two more challenging ones. Remember that viewing these objects is much more rewarding if you have a dark sky and use averted vision.

Eleventh magnitude NGC 986 (02 33 34.1, -39 02 47) is quite an easy object showing a well-defined, almost stellar condensation that is slightly off-centre in a hazy spot. You get NGC 1079 (02 43 44.4, -29 00 11) if you suffer from dyslexia when keying in NGC 1097. It's quite a nice galaxy though, somewhat elongated NS and with a bright central condensation.

ESO 356-G4 (02 39.9, -34 32) is the Fornax dwarf galaxy. At magnitude 7.5 it sounds as if it should be an easy object but this is definitely not the case, because the diameter of 20' means it has an extremely low surface brightness. If you have a rich-field telescope with excellent high-contrast optics and an extremely dark sky you might have a chance but don't even think about it from in Canberra. The globular clusters associated with the Fornax dwarf are a different matter, however, and several are visible in amateur telescopes. The secret to observing these objects is to remember that they are small, and need a reasonable amount of magnification. The two brightest are NGC 1049 (02 39.7, -34 17) and ESO 356-SC08 (2 42.4, -34 06), both appearing as slightly nebulous stellar points at 127x.

The barred spiral NGC 1097 (02 46.3, -30 17) is, by contrast with the Fornax dwarf, one of the best galaxies in Fornax. In the C11, the central bar and the distinctly oval core are very prominent and I had some suspicion of the spiral arms as well. A satellite galaxy, NGC 1097A, is a bright hazy spot about 3.5' away. The C14 gives a similar view but the central bar and core seem to be enclosed in a hazy cloud.

The next galaxy that I picked, ESO 299-G020 (02 49.6, -38 46), is a far more difficult proposition at magnitude 13.8, but can still be seen without too many problems with some use of averted vision.

With NGC 1316 (03 22.7, -37 12) we enter the Fornax cluster. This galaxy is generally classified as the brightest member and is a quite featureless elliptical haze with NGC 1317 apparent 6'.5 to the north. Images of NGC 1316 show faint complex dust lanes vaguely similar to those in NGC 5128.

A galaxy that I hadn't looked at before is NGC 1326 (03 23 56.3, -36 27 53). This is similar to those viewed previously with a slightly off-centre stellar condensation immersed in an area of haze. About 20' away in an ENE direction is the interacting pair NGC 1326A and NGC 1326B. These are quite difficult at about 14th magnitude and a real averted vision job in my sky.

The Fornax cluster is obviously a great area for galaxy hunting and I won't go into too much detail about it. A good place to start is to centre your telescope at approximately RA 3h 35m, dec. -35º 40'. An eyepiece of one degree field at this position will show at least nine galaxies in a 15 cm telescope (NGC 1374, 1379, 1380, 1381, 1387, 1399 and 1404). NGC 1381 is a rather good example of an edge-on galaxy which the C14 shows as a bright streak with a noticeable bright central bulge.

Perhaps the finest galaxy in Fornax is NGC 1365 (03 33.6, -36 08) which lies almost exactly 10º due south from NGC 1360. This barred spiral is not the brightest galaxy in the constellation, but is a particular favourite of mine because of the amount of structure visible in relatively small telescopes. The central bar and spiral arms are clearly seen under a dark sky in a 20 cm telescope, and may be visible with even smaller apertures. This galaxy, in common with NGC 1316, is traditionally regarded as a member of the Fornax cluster but it may in fact be a foreground object.

The final galaxy that I looked at was NGC 1425 (03 42 11.4, -29 53 36) which is another quite bright one. It showed some N-S elongation and had a bright but ill-defined core.

CONSTELLATIONS OF THE MONTH - The Ten Best Southern Planetaries

Albert Brakel

When William Herschel stumbled across round nebulous blobs in the sky in the 18th Century, he had no idea what they really were, so as they had the rough apparent sizes and shapes of planets, he called them planetary nebulae (PN). Today we know that they are shells of gas puffed out from dying stars. A more appropriate name would be something like cocoon or shell nebula, but we're stuck with the old term. Here I give my impressions of which ones I think are the best 10 in the southern sky. This list includes only those objects south of the celestial equator, so it does not contain well-known northern showpieces such as the Dumbbell, Ring and Eskimo Nebulae. Not surprisingly, they are found in or around the southern Milky Way. The planetaries are given in order of right ascension rather than in any order of merit, and at this time of year you can start with the first, and progress onto the later ones in the months to come. An OIII filter usually makes them more impressive than in an unfiltered view.

NGC 2438 ("The planetary in the cluster") - Puppis (07h 42m, -14º 49'). This one is included not so much for its own sake but because of its outstanding setting, in the northeastern part of the open cluster M46 in Puppis. It is pale bluish, easy to see, and 60" in diameter. Close inspection shows that its outer perimeter is a bit brighter than the rest. The cluster isn't too bad either - rich, about 25' across, and broadly concentrated towards the centre. The PN is not actually part of the cluster but lies in front of it, about 3250 l.y away, compared to the cluster's 5540 l.y. There is another planetary, in Pyxis, that really is part of an open cluster, NGC 2818, but it's fainter.

NGC 3132 (The Eight-Burst Nebula) - Vela (10h 07.7m, -40º 26'). A reasonably bright nebula comparable in angular size to Jupiter, this object varies in appearance according to what telescope, magnification and filter you use. At low mag. it appears as a hazy patch around a 10th magnitude star, and needs an OIII filter to enhance it. 150x or higher powers show it well without the filter. It displays a solid grey disk with a suggestion of brightening around the periphery, some sections of this outer ring being brighter than others. The true central star is a mag. 16 white dwarf, not the obvious mag. 10 star. The nebula gets its name from the complex multilayered rings stacked on top of one another at different tilt angles, but these are mostly not apparent visually.

NGC 3242 (The Ghost of Jupiter Nebula) - Hydra (10h 24.8m, -18º 38'). Easy to see at any magnification, this is one of the sky's brightest PNs. As its name suggests, it is about the angular size and shape of Jupiter. It has a slightly flattened, uniformly lit, pale greenish disk, fading only at the edges. Larger scopes show a spindle of light inside the disk, in which is set a central mag. 11 star.

NGC 3918 (Herschel's Blue Planetary) - Centaurus (11h 50.3m, -57º 11'). Although only 12" across, this nebula is bright enough to see with a small scope. Look for it on the extension of the short arm of the Southern Cross, beyond Delta Crucis at about the Beta-Delta distance. It is a distinctly pale blue, well-defined round disk. John Herschel discovered it in 1834.

NGC 4361 (The Corvus Planetary) - Corvus (12h 24.5m, -18º 46'). A grey disk with the central portion being reasonably bright and smaller in appearance than Jupiter. Surrounding this to about 2 Jupiter radii is a faint outer halo, the boundary between the central and outer regions being gradational. Averted vision or an OIII filter help increase the contrast a bit. It looks better at lower powers (less than 120x), as higher powers reduce the surface brightness too much. The central mag. 13 star requires either averted vision or a large aperture.

NGC 5189 (The Spiral Planetary) - Musca (13h 33.5m, -65º 59'). For a long time no-one was sure what this object actually was, because it is most unusual for a planetary nebula. Instead of the usual rounded form, the nebulosity consists of a knot of greyish light with an irregular internal structure, and is roughly elongated with a bright bar in the E-W direction. To some people it's reminiscent of a barred spiral galaxy, hence its name. It is clearly visible without a filter at low power, but needs higher powers or an OIII filter to bring it out to better advantage.

IC 4406 (The Retina Nebula) - Lupus (14h 22.4m, -44º 09'). An intriguing object with a distinct squarish shape, 28" across, and relatively high surface brightness. At low powers it is just a bluish-grey disk, but the rectilinear outline becomes apparent at 150x (or even 120x if an OIII filter is used) when observed carefully. The northern and southern sides of the square are well defined, the other sides more blurred. This is because it is an example of an extremely bipolar PN, with two long streamers oriented east-west. The N and S sides of the square represent the sharp edges of the streamers, while the E and W sides are where the streamers become too faint to see. I used to refer to it informally as the "Box Nebula", but someone else has since applied that name to another object. When the Hubble Space Telescope examined it, the central region was seen to be textured with a delicate network of veins, like the retina of the eye, so it has been known since as the Retina Nebula.

NGC 6302 (The Bug Nebula) - Scorpius (17h 13.7m, -37° 06') - has a high surface brightness, so it is obvious as a concentrated, elongated (1.5') object that is fuzzy and unstarlike even with direct vision. It really stands out with an OIII filter. It gets its name from its insect-like appendages in photos. The Hubble Space Telescope image is spectacular, showing a bipolar nebula with angular spikes coming off. Its structure suggests a young planetary nebula whose parent star (mag. 10) burped a ring of ionized gas and later drove off its outer envelope with fierce stellar winds.

NGC 7009 (The Saturn Nebula) - Aquarius (21h 04.2m, -11º 22') - is readily distinguished from stars, at about 80x power, as a small, bright, circular patch with a definite greenish tinge. Higher powers reveal a 25" disk with uniform brightness, except for the unsharp edges. The nebula gets its name from the "flyers" or ansae that project from it in opposite directions and give it a superficial resemblance to Saturn. In reality, these are hard to see, but on a night of exceptional seeing a 30-cm or 40-cm aperture may show them spanning 44". For an extra challenge, see if you can spot the brighter condensations at the ends of the ansae. The best I've been able to manage so far has been to see the nebula as elongate in the E-W direction with 360x, without resolving the ansae.

NGC 7293 (The Helix Nebula) - Aquarius (22h29.6m, -20º 49'). This is the second closest planetary nebula to Earth, lying 520 l.y. away. That should make it one of the brightest PNs in the sky, and with an integrated magnitude of 6.5, it is. Just one problem - its light is spread out over a disk 13' across, so that the perceived surface brightness is low, giving it a low contrast against the sky background. It can be detected as a very subtle circular glow almost half the diameter of the Moon, using about 80x magnification on a 20-cm scope. With about 120x and a broad-band nebular filter, a dark central "hole" becomes visible. An OIII filter enables the central "hole" to be seen with lower power, and makes the nebula brighter, but it is still a low surface brightness object. On photographs it has a shape resembling a helical coil, caused by multiple outbursts from the central star. Visually the helix structure is not obvious, though the NW and SE sides can be perceived as brighter than the rest. Some foreground stars are scattered across the disk, but the central mag. 13 star is difficult for 20-cm and really needs a larger scope.

A Bonus PN
Now that I've described the 10 best, I find that I can't resist adding just one more, because it's a fairly bright PN that is not as well known as it should be. This is NGC 3195 in Chamaeleon (10h 08m, -80º 53'), lying half-way between Delta and Zeta Chamaeleontis. The nebula appears as a grey, uniform, circular glow, about 30" across, lying within a quadrilateral of field stars. An OIII filter does not reveal any structure.