Constellation of the Month - Reticulum

Albert Brakel

Reticulum is a small constellation centred on the group of mag. 3.4-5 stars just NW of the Large Magellanic Cloud, and about halfway between Canopus and Achernar. It was first published by Isaak Habrecht of Strasbourg as the Rhombus (which it sort of resembles), but was renamed by Lacaille in 1752 as Reticulum Rhomboidalis, as a memorial to the eyepiece reticle he used for his observations. Mercifully this was shortened to Reticulum by the IAU, so the name now means the Net, instead of the network of lines in a reticle (perhaps appropriate for the computer age??).

The constellation lies far from the Milky Way, so it's not surprising that the only objects of telescopic interest are galaxies and double stars. For my observations I used the 14" Bobroff reflector in the CAS Dome at Mt Stromlo.

Before starting off with the telescope, it's worth scanning the area around Alpha Reticuli with binoculars. The stars in this area have a variety of colors, mostly orange, yellow and red. They give the impression of a spread-out open cluster, but the stars are too far apart in space to be gravitationally bound. Yet they all have a similar proper motion (except for Delta Reticuli), suggesting that they had a common origin in a cluster that has since dispersed.

Alpha Ret (RA 4h 14.4m, Dec -62° 28' 26") itself is a very wide double star, 134 light years distant. The primary is a mag. 3.4 golden yellow, with the secondary 49 arcseconds away to the north. But here's the catch – the companion is only mag. 12.0, so if this is beyond your limiting magnitude for the night, forget it. You could use this as a test for the seeing.

Less than a degree to the SE, Theta Ret (Rumker 3) (4h 17.7m, -63° 15' 20") is set in a pretty field of scattered stars, and consists of a mag.6.1 primary that appeared whitish with a hint of yellow, accompanied by a mag. 7.8 star 4.0" away that is a dim and deeper yellow. It was just resolved with 140x, but more convincingly with 220x. The binary was discovered by the old Parramatta Observatory in the 19th century.

Between Alpha and Theta you will no doubt have noticed an obvious luminous patch, that is one of the brightest galaxies in Reticulum, NGC 1559 (4h 17.6m, -62° 47'). This mag. 10.4 barred spiral showed up as a uniform elliptical glow, without perceptible structure, tapering off in brightness towards the edges. It sits in a field of foreground stars, one of which could be seen with averted vision in front of the galaxy, SW of the centre.

Moving now to the eastern border of the constellation, just N of the Mira-type variable R Reticuli (4h 33.5m, -62° 02' – mag. 6.5-14, period 278.3 days) we find the binary h3760 (4h 33.6m, -62° 49' 26"). Component A (mag. 5.8) is a bright orange sun, followed 32" to the east by the much fainter yellowish-white B star. The latter has been described as ice-blue in color, but this is probably a color-contrast effect in the eyes of some observers.

Getting back to galaxies, NGC 1543 (4h 12.8m, -57° 44') lies 1.6° north of Epsilon Ret in the NE of Reticulum. Its integrated magnitude of 10.6 is only slightly fainter than NGC 1559, but it's more extended, which makes all the difference. Careful observation shows a not-very-obvious E-W-elongated smudge, that disappears from view when there is the slightest haziness in the air.

NGC 1574 (4h 22.0m, -56° 58'), 1.5° to the NE on the border with Dorado, is more conspicuous with an integrated magnitude of 10.5 and a higher surface brightness. It appeared as small, round, and reasonably bright, with a tiny, distinct, almost stellate nucleus. To its east lies a mag. 7.5 star, that happens to be the binary Rumker 4 in Dorado.

NGC 1313 (3h 18.3m, -66° 30'), our last galaxy, lies in the opposite SW corner of the constellation. It looked like an oval hazy area, without any distinct structure or nucleus, although photographs show it as a distorted barred spiral. It has a N-S elongation. Three faint foreground stars are embedded in the luminosity, the brightest one SSE of the centre, another at a greater distance to the NW, and the third one, so faint that it was visible only intermittently with averted vision, closer in to the N.

Four degrees directly north of NGC 1313 is the fine optical pair of Sun-like stars, Zeta Reticuli 1 & 2 (3h 18m, -62° 30'), much beloved of UFO buffs as one of the home places of alien visitors (do a Web search on Zeta Reticuli and you'll see what I mean). Makes an excellent binocular pair 5 arcminutes apart, and if you're really sharp-eyed you can resolve the mag. 5.2/5.5 stars with the unaided eye. They are relatively close at 39 light years from us. According to one reference, they lie about 3 l.y. from each other, which would put them too far apart to be physically connected, but as they have the same proper motion through space, possibly they may be the remains of a disrupted binary system (my speculation).

Kappa Ret (3h 29m 23s, -62° 56'15"), 1.6° to the ESE, is a wide double 54.1" apart. The components are a yellow mag. 4.7 star with an ashen mag. 10.3 companion to the east, easily seen with 140x. The system is about 65 l.y. distant.

Dunlop 14 (3h 38m 10s, -59° 46' 35"), another Australian discovery, lies 3.3° NNE of Kappa. It's another wide double with almost 1 arcminute separation (57.5" actually), this time located 186 l.y. away. Mags. 7.1 and 8.9, both are pale yellow F-type stars.

If you've never observed in Reticulum before, give it a go. Even small 'scope users will see most of the objects without trouble.

The Galaxies of Caelum

Jenni Kay, FRAS

Caelum is not a very prominent constellation to pick out in the sky with only the two brightest members, Alpha and Beta, being obvious enough to detect with the naked eye. Even so, with a good field-guide star chart to locate the constellation, it doesn't take long to pick it out. First up, in the general area of Caelum, it is useful to look for the four bright stars in Fornax shaping a prominent trapezium. These stars are Upsilon 1, 2, 3, and 4. Next, move slowly a short distance in the direction of south and the next two stars to be easily seen are Alpha and Beta Caeli. In this part of the sky, in general, there are only a few stars spread out over the wider sky, and they do not form any easily recognisable shapes.

Overall, I found this to be a neat little constellation to work through, being neither overly rich nor large in size. Therefore, it made a great little project for one to two nights worth of work. Plus, there were numerous bright field stars as seen through the 8x50mm finderscope, making it easy to follow star trails to navigate through the constellation as I moved from one target to the next.

The following observations were made with a 12.5" f/5 Newtonian, from my semi-rural home site in Lobethal, SA. Typically, the skies here have a limiting naked eye magnitude of 6.1, with the seeing rated at Antoniadi II-III.

NGC 1558 : 04 19.3 -45 02 12.5 visual magnitude (v); 2.6' x 1.0'; Surface brightness (SB) 13.4v; Position angle 72d.

83X: Very obvious, relatively bright, relatively long, elongated WSW-ENE, with a smooth and even glow throughout. There is a very bright 7.1 mag field star nearby to the east, showing a striking yellow/white colour, but this does not overpower the glow of the galaxy.

150X: much improved - relatively bright, long and broad, 1.5' x 0.5' in size, that gradually brightens towards the centre. The galaxy shows a high surface brightness.

NGC 1567 : 04 21.1 -48 15 (12.2v; 1.3' x 1.2')

83X: obvious enough with averted vision and care as a faint, small, round, hazy spot with a brighter, almost stellar nucleus.

150X: Greatly improved view - relatively faint, round, 30" in size, with an almost stellar nucleus equal to a 13th mag star in brightness. The galaxy lies in an attractive bright star field with many 10th mag stars, and while there are no star patterns in the field the galaxy is easy enough to notice, especially with averted vision.

NGC 1570 = NGC 1571

It is considered that NGC 1570 is non-existent being a duplicate for NGC 1571. It was Sir John Herschel who discovered both NGC 1570 (h.2637) and NGC 1571 (h.2638) on two different nights. Since he does not mention both galaxies on either night, and since his visual descriptions and positions taken are similar (~3.1' separation), he was probably looking at the same galaxy on each night. Furthermore, there is only one galaxy here.

NGC 1571 : 04 22.2 -43 38 (12.2v; 1.9' x 1.4'; SB 13.1v; PA 178d.)

83X: obvious, relatively faint, small, round, hazy spot.

150X: Improved view - relatively bright, round, 30" in size, with a smooth, high surface brightness and brightens to a very small, round, central core. The alaxy lies at the eastern end of a chain of three 13th mag field stars shaping an arc. There is also a neat little 11th mag double star 3.0' to the NE.

MCG-7-10-2 : 04 22.2 -43 58 (13.0v; 0.8' x 0.6'; SB 12.1v) 21.0' south of NGC 1571.

150X: Needs much care to detect: extremely faint, round, 30" in size, with a smooth and low surface brightness. While the galaxy is such a faint object, in moments of better seeing it can be caught strongly with averted vision.

NGC 1572 : 04 22.6 -40 36 (12.6v; 2.2' x 1.0'; SB 13.3v; PA 148d.)

83X: Obvious enough, relatively bright, small, round, hazy spot, with a 12th mag field star close to the eastern edge.

150X: Improved view – relatively bright, round, 40" in size, with an even surface brightness, and brightening towards the centre. In the wider general field there are many long chains of bright stars.

NGC 1585 : 04 27.5 -42 09 (13.5v; 1.3' x 0.9'; SB 13.5v; PA 154d.)

83X: Takes a few moments to notice being a shy, soft glow against a star that lies in a bight star field. However, with care and averted vision the galaxy can be seen with confidence as a relatively bright, small /very small, round, hazy spot, attached to a 12th mag star in the west.

150X: Improved view - relatively bright, round, 30" in size, with a high surface brightness and brightens to the centre. There is a bright field star to the NE with a strong yellow colour. IC 2068 lies nearby to the NW.

IC 2068 : 04 26.6 -42 05 (13.3v; 1.3' x 0.9'; SB 13.3v; PA 162d.) 11.0' NW of NGC 1585.

83X: Requires much care, patience, averted, and then only suspected as an extremely faint, fuzzy starlike object.

150X: Much improved - faint, round, 30" in size, with a brighter nucleus within a very faint halo. The nucleus is equal to a 13th mag star in brightness.

NGC 1595 : 04 28.4 -47 49 (13.7 (B); 1.3' x 0.8'; SB 12.4; PA 170d)

83X: The SW of a close pair. Obvious, relatively faint, small, round, hazy glow that brightens towards the centre.

150X: Improved view – relatively bright, round, 30" in size, brighter towards the centre. The halo gradually fades towards the edges and it is the brighter central core area that catches the eye first. NGC 1598 lies to the NE.

NGC 1598 : 04 28.6 -47 47 (13.8(B); 1.4'x 0.8'; SB 12.6; PA 123d.) 2.8' NE of NGC 1595. Slightly fainter than N1595.

83X: Obvious - faint, small, round, hazy glow.

150X: Improved view - faint, oval in shape, 40" x 35" in size, with the major axis lying NW-SE. The galaxy has a smooth surface brightness, and there may be either a brighter core plus a superimposed star, or two superimposed stars within the glow. In the wider, general view, there is a light scatter of a few stars, and a neat little double star 11/13 mag to the NW.

NGC 1616 : 04 32.7 -43 43 (12.8v; 1.7' x 0.9'; SB 13.1v; PA 34d.)

83X: Obvious, especially with averted vision: relatively faint, small, round, hazy spot with a brighter stellar nucleus.

150X: Improved view – relatively faint, round, 40" in size, smooth and even glow throughout, with a brighter stellar nucleus equal to a 13th mag star in brightness.

NGC 1658 : 04 44.0 -41 27 (13.5v; 1.5' x 0.5'; SB 13.0v; PA 124d.)

83X: The NW of a close pair. Needs care and averted vision; extremely faint, small, hazy smudge, possibly elongated.

150X: Still difficult, but can be seen with more confidence - extremely faint, elongated SE-NW, 45" x 15", very low and even surface brightness, with a brighter middle. There is a long chain of 11/12 mag field stars which leads to this faint pair of galaxies. NGC 1660 lies to the SE.

NGC 1660 : 04 44.2 -41 29 (13.9v; 1.0' x 0.4'; SB 12.8v; PA 31d.) 3.0' SE of N1658. Needs care - extremely faint, possibly elongated, hazy smudge.

150X: Improved slightly - extremely faint, elongated SW - NE, with a size of 45" x 15", and a smooth glow throughout.

NGC 1668 : 04 46.1 -44 43 (12.7v; 1.5' x 1.0'; SB 13.0v; PA 104d.)

83X: Obvious enough, especially with care and averted vision - very faint, small, round, hazy spot, that brightens to a stellar nucleus, and there is a 13.5 mag star at the NE edge.

150X: Improved - very faint, round, 30" in size, with a low and even surface brightness, and there is a brightening to an almost stellar nucleus. In the general field there is a light scatter of mostly 12th mag and fainter stars, with one 9th mag star to the NE.

NGC 1679 : 04 50.0 -31 59 (11.5v; 3.0' x 1.5'; SB 13.0v; PA 145d.)

83X: very obvious, and seen as soon as it moves into the field – relatively bright, relatively large, round to oval in shape. There are three field stars shaping a triangle over the galaxy. There is a 13th mag star at the SE edge, a 12th mag star at the NW edge, and another 12th mag star off the SW edge.

150X: Improved view - relatively bright, oval in shape, major axis is SE - NW, 1.0' x 45" in size, with a smooth, high surface brightness.

NGC 1687 : 04 51.3 -33 56 (13.8v; 1.3' x 0.5'; SB 13.2v; PA 45d.)

83X: Very dim, requires care to detect with any confidence, and then, only in moments of better seeing the galaxy is extremely faint, round to oval in shape, and small.

150X: Slight improvement, and in brief moments of better seeing - extremely faint, small, round, 25" in size, with a very smooth and low surface brightness. Suspect there may be an almost stellar, brighter nucleus. The galaxy lies in a bright star field with stars in long chains and rows.

NGC 1701 : 04 55.8 -29 53 (12.8v; 1.2' x 1.0'; SB 12.8v; PA 134d.)

83X: Obvious enough, especially with care and attention - faint, small, round, hazy glow. There is a bright 10th mag field star off the SE edge, but this star doesn't overpower the galaxy glow. 150X: Improved – relatively faint, round - oval, 40" in size, with a very smooth and even high surface brightness.

NGC 1759 : 05 00.8 -38 43 (13.1v; 1.1' x 1.0'; SB 13.1v; PA 154d.)

83X: Requires care, averted vision, and then only suspect an extremely faint, small, probably round hazy glow. 150X: Improved enough for confident sighting - extremely faint, round, 30" in size, very low surface brightness. The galaxy is only glimpsed in moments of better seeing, and sometimes the view is strong. The galaxy lies in a line with 12th mag field stars crossing the field SW - NE. The galaxy is 3rd from the NE end.

Ross Gould covered both Caleum and Columba in the April 1999 Southern Cross.