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Southern Cross - December 1999

• Constellation of the Month - Horologium
• Polar Alignment with a Notebook Computer
• The Lindsay Star Clusters of the SMC - Part 2

Constellation of the Month - Horologium

Steve Crouch

Horologium was added by Lacaille in 1752 and is situated to the south of Eridanus, virtually opposite to Fornax on the other side of Eridanus. In common with most of the constellations introduced at this time, it's a rather drab affair. The brightest star is only magnitude 3.8 and it has to be said that there is nothing much here for the small telescope except for the globular cluster NGC 1261 and perhaps one or two of the brighter galaxies. Double star fans will also be disappointed if they expect to find anything worth hunting down. Galaxies are, however, present in abundance and this is therefore a very interesting constellation for the galaxy hunter who happens to possess a medium to large telescope (20cm upward). As usual, I performed most of my observations with a C14 and a 35mm panoptic eyepiece giving a magnification of 111 times. I observe from Theodore which has reasonably good skies for a suburban location.

1. Globular Clusters
   
   Horologium has two, the quite easy NGC 1261 (03 12.3 -55 13) and the impossibly faint AM-1 (03 55.0 -49 36). NGC 1261 is a well condensed and reasonably bright globular whose outer regions were well resolved at 111x. The central condensation appears somewhat wedge-shaped with the thin edge of the wedge pointing roughly to the north. I did not attempt AM-1 as it appeared quite beyond my capabilities at magnitude 15.9 but it may be worth hunting for with telescopes of greater than 50 cm in aperture under a very dark sky. As a guide to location, it is contained within a small triangle of magnitude 14 stars.
   
   
2. Galaxies
   
   First on the agenda was NGC 1249 (03 10.1 -53 21) which showed up as a reasonably bright, roughly elliptical haze aligned roughly E-W. NGC 1356 (03 30.7 -50 17) is much fainter but was still reasonably easy in the C14. There are two wide double stars in the field and the galaxy is situated near the northern star in the North-South oriented pair. We next come to NGC 1433 (03 42.0 -47 13), a nice bright galaxy with a somewhat off-centre very bright nucleus. NGC 1448 (03 44.5 -44 39) is an excellent example of an edge-on galaxy. I could not see any central condensation. NGC 1512 (04 03.9 -43 21) again showed up very brightly. This galaxy is a barred spiral of the "theta" type (looking like the Greek letter theta) and I could see definite indications of the bar in the C14. NGC 1510 (04 03.5 -43 25) is a smaller and fainter galaxy a short distance to the southwest from NGC 1512. I wound up my galaxy hunt with IC 1933 (03 25.7 -52 47). This is the most prominent of a group of IC galaxies in this region of Horologium and I saw it as a fairly prominent NW-SE ellipse with a star on the northwestern end.

The galaxies mentioned are just a sample and there are many more for the dedicated observer to log. In any case, I hope everyone enjoys Horologium.

Polar Alignment with a Notebook Computer

Brad Wilson

Polar alignment has always been the bane of my astronomy lifestyle. When it's dark and cold and you've travelled a long way to do some precious observing, who wants to spend endless minutes trying to line the telescope up on a blank piece of the sky called the South Celestial Pole? If like me, you've tried the Star Drift method, you will know it takes forever, not to mention how hard it is to reverse your thinking when trying to figure it out from a method written for the Northern Hemisphere.

Then of course there is the direct method, lining up the scope's polar axis on the Celestial pole. This is an exercise in severe neck strain. It's hard enough just to find the star Sigma Octantis. Finding the actual pole from there is quite tedious. Then to actually juggle your scope into position is truly a nightmare.

Fear not. The method I use is easy for a computer nerd and requires little physical effort. What you do is get hold of a cheap notebook computer. Mine cost thirty dollars at a garage sale. It is a 386sx with an LCD B&W screen. In other words it is a slow piece of junk with a lousy screen, but hey, who cares? The Pentium can sit at home waiting for the important jobs (like playing Flight Simulator).

This computer is for real field work. As this computer wanted 240 volts I had to bypass the transformer and supply it with 6 volts from a motor cycle battery. I have 2 batteries (about eighteen dollars each) that supply power all night. They get a recharge from the battery charger the next day. Obviously though, a notebook that already runs on batteries is an easier way to go.

Now to the nitty gritty. Loaded on the computer is "Skyglobe", a common DOS shareware astronomy program, downloadable from the net (or if you need a copy see me). However I'm sure many other astronomy programs would do the job just as well. When I get to my observing site I turn on the computer, make sure the clock is on the right time (important) and then run the program. Out in the bush even a crappy LCD screen is amazingly bright (you could almost spotlight possums with it). Because of that I have red cellophane blu-tacked to the screen to maintain my night vision. This works quite well. The program is running in real time and set to Canberra co-ordinates so it matches the actual sky.

On the screen I look for a star in the north or south that will shortly culminate, preferably near the horizon, to get higher accuracy. Then I line my scope up roughly north and south (easy business for even a neophyte). Then I rotate the RA axis (the fork arms on my SCT, or the bar with the counterweights on a German Equatorial Mount) into the horizontal position, which allows the tube to swing along the meridian line.

I lock the RA axis and leave the clock drive off. Then using the setting circles I set the declination to Canberra latitude (35º South) and lock the Dec axis. The scope is now pointing to the zenith. I check the accuracy with a builders level set across the mouth of the tube in a North-South, then an East-West direction. I then shim up the tripod to get it all level.

I generally have to wait at least ten minutes or so before a bright star near the horizon crosses the meridian (on the computer screen). While I'm waiting I'll identify the star in the real sky. If I just can't wait I'll pick a dim star or a star that's higher up in the sky. A minute or so before the chosen star culminates I unlock the Dec axis and swing the tube down to the star. The next thing is to move the whole scope by grabbing the tripod legs and dragging it into position until the star is visible in the finder. Then I make small adjustments with the Dec axis and the tripod legs until the star is centred in the eyepiece of the scope (a low power is sufficient).

Now the scope is polar aligned. But just for accuracy's sake I check the declination of the star (shown on the computer). If the Dec circle on the scope is wrong then I adjust the declination control till it's correct, then raise or lower the tripod legs along the North-South line to get the scope pointed back on the star.

Finally I turn on the clock drive and adjust the RA circle to the current Sidereal Time. The Sidereal Time just happens to be the RA of the star (shown on the computer). The further benefits of running Skyglobe is it will give the coordinates of any planet or Messier Object as well as a lot of other NGC objects. Finding galaxies becomes a lot easier.

Using the setting circles puts the object in the finder scope, and if you're lucky, in the actual eyepiece. Now that the scope is polar aligned you can also do astrophotography. Another benefit is that on a motorised drive the object being observed will remain centred in the eyepiece. On a non-motorised equatorial mount, adjustment will be needed in RA only.

Getting a good polar alignment with little effort within 15 minutes is a good feeling. Not only does your astronomy become easier but it's nice to know you've now got a "fix" on the heavens. You are now "in sync" with the universe as it rotates above you. Plus if you get bored, you can always play "Lunar Lander" on the computer...

The Lindsay Star Clusters of the SMC - Part 2

Jenni Kay, FRAS

Last month we began a tour of the SMC, seeking out some of the brighter star clusters from E. M. Lindsay's catalogue published in 1958. As mentioned previously, while none of the Lindsay clusters listed in my observing articles have a duplicate identity with existing NGC or IC clusters, some do have an alternate Kron designation, and these I have included.

All of the following observations were made with a 12.5" f/5 Newtonian from my semi-rural home site in Lobethal, SA. The skies here typically offer a limiting naked eye magnitude of 6.1, with the seeing rated at Ant II-III. While I might class many of these clusters as being somewhat difficult to pick out, they could be detected well enough for a confident sighting when care and patience was applied. I found the best view was attained at highest magnification, in my case this was at 150X.

Li 39 : 00 49 03 -73 21 40

150X: with much care, the cluster can be detected as a relatively faint, relatively large, round, hazy glow, 1.0' in size. The glow appears mostly smooth, and a little grainy, with at least one star near resolving at the eastern edge. There is a bright field star detached and immediately north-west of the soft glow. This is a very rich, starry region of the SMC, therefore some care and patience is needed to find the cluster. NGC 267 lies almost 7.0' north-west of Li 39.

Li 40 : 00 50 40 -72 57 52

150X: Obvious, relatively bright, relatively large, hazy glow, with an irregularly round overall shape, 2.0' in size. There are about five 14 mag. stars scattered across the hazy glow, and three 13 mag. stars lying in a row along the northern edge of the cluster. Li 44 lies about 5' east. In the wider view, this is an exceptionally rich area, being the bright bar of the SMC, which is densely packed in stars and small, hazy glows from other nearby clusters and nebulae.

Li 41 : 00 50 56 -72 43 44

14' north of Li 40. 150X: obvious enough as a relatively bright, very small, round, hazy spot, about 25" in size. I suspect this is a tight cluster as the brightness of the glow is even throughout from edge to edge. The cluster lies with four 13 mag. field stars in a cruciform shape. This asterism acts as a good signpost to locate the cluster.

Li 43 (Kron 28): 00 51 42 -71 59 54

Too faint for me to detect.

Li 44 : 00 51 53 -72 57 11

14' south-southeast of Li 41. 151X: Obvious, relatively bright, relatively large, mostly round, 40" in size, with a smooth even glow throughout. I suspect there may be one to two stars on the verge of resolving.

Li 45 (Kron 30) : 00 52 35 -72 11 43

About 4' east of NGC 299. 150X: relatively bright, large, round, hazy glow, with five 13/14 mag. stars loosely scattered across the glow. Overall, the size is 70". The soft cluster requires a little care to notice, being a little lost among the brighter stars of a large, more prominent star group. Also in the near vicinity lies NGC 306, and Li 51.

Li 46 (Kron 31) : 00 53 00 -72 53 40

8' northeast of Li 44. 151X: With averted vision, and much care, the eye barely perceives the extremely faint glow from this cluster. It appears as a large, irregularly round glow, about 1-2' in size, with a faint star involved. There is a pair of 12 mag. field stars at the north-eastern edge. The cluster glow is so faint there is some difficulty in estimating the size better than I have given. While the glow is faint, the eye is pulled to it with averted vision, and a confident sighting can be determined.

Li 48 : 00 53 28 -71 23 55

110/150X: obvious, relatively bright, small, round — oval in shape, hazy glow, with a size of 30" x 25" slightly elongated east to west. The hazy glow is smooth and even from edge to edge. The cluster glow forms a triangle with two faint stars in the south.

Li 51 : 00 54 55 -72 06 45

8.5' north-east of NGC 299. 150X: obvious enough in a search for it as a relatively bright, small, soft, hazy smudge, slightly elongated north to south, with two stars near resolving. Overall, the size is 40" x 20". There are some faint stars loosely gathered around the cluster, and while these stars do not appear to be associated with the cluster, they do add visual appeal to the general view.

Li 53 (Kron 34) : 00 55 49 -72 49 56

150X: Obvious and eye-catching, as a bright, small, round, hazy glow, about 25" in size. The cluster lies in a very rich star region, but even so, it is still obvious enough to easily find.

Li 55 : 00 56 39 -73 54 15

Too faint for me to detect.

Li 56 : 00 57 30 -72 15 52

9' southwest of NGC 346. 150X: Very obvious, as a bright, relatively small, round, hazy glow, with a smooth and even brightness from edge to edge, and a size of 30". Lies in a very rich part star field.

Li 63 (Kron 42) : 01 00 34 -72 21 55

2.5' east of IC 1612. 110X: obvious as a very small, almost stellar, relatively bright, hazy spot. 150X: Improved view — very small, round glow, about 10" in size. There is a field star just off the north-west edge.

Li 64 (Kron 43) : 01 00 53 -73 20 24

150X: needs averted vision and some care to detect being a very faint, relatively small, round, hazy glow, with a size of 35". In the wider view there are few field stars and the background sky is smooth, therefore, there is sufficient contrast between the sky and cluster glow to pick it out with full confidence.

Li 66 : 01 01 45 -72 33 52

~25' east-southeast of NGC 330. 150X: Obvious enough, although only the brightest members were detected, appearing as a dainty chain of three stars in a row, lying almost east to west, with all stars very close together and similar in brightness at 12 mag. Overall the size is 50" x 10".

Li 68 (Kron 44) : 01 02 04 -73 54 45

150X : extremely faint, relatively large, very soft, round, hazy glow, with a size of 1.5'. The cluster glow is so faint, I would almost class this a borderline object, but I am able to catch it on several occasions with confidence. In the rest of the field there is a light sprinkle of 13 mag. stars, and the background sky is smooth.

Li 70 (Kron 47) : 01 03 11 -72 16 18

110X: very obvious and catches the eye as a relatively faint, very small, round, hazy spot. It lies near the outskirts of the very large, bright, stellar association south of NGC 371. 150X: Improved view — relatively bright, round, 30" in size, with a smooth, even glow from edge to edge.

Li 74 (Kron 50) : 01 04 36 -72 09 37

83X : catches the eye, relatively faint, very small, almost stellar, hazy speck. 110/151X: More obvious, relatively bright, small, irregularly round, 25" in size, with a smooth glow throughout. 163X: now and then I can catch two stars resolving within the hazy glow.

Li 79 (Kron 54) : 01 06 47 -72 16 16

8' northwest of NGC 416. 150X: with averted vision, the cluster can be detected as a very faint, small, round, hazy glow, about 20" in size. There is a 12th mag. field star at the northern edge.

Li 80 : 01 07 15 -72 45 57

~6' northwest of NGC 419. 150X: obvious enough with averted vision as a very faint, relatively small, round hazy glow, with a size of 35". A 13 mag. field star lies west of the soft cluster glow.

Li 84 : 01 08 20 -72 00 07

Too faint for me to detect. This cluster lies within the bright and obvious nebula Henize (Hen) 80. The nebula is obvious visually, but I cannot detect any sign of the cluster within.

Li 100 : 01 18 16 -72 00 09

150X: With care and averted vision the cluster can be detected with confidence appearing as an extremely faint, relatively small, round, soft hazy glow, about 30" in size. The cluster lies between a 12 mag. field star and a row of three 11/13 mag. field stars. In the rest of the field there are only a few stars, and the background sky is smooth.

Li 113 : 01 49 28 -73 43 44

42' north-west of NGC 796. 110X: With averted vision, the cluster appears as an extremely faint, large, probably round, hazy glow, with a size of 1.5'. While the cluster is so faint, it can be held with averted vision continuously, and a confident observation can be made. 150X: Inferior view, the cluster is too faint at this power.

Li 114 : 01 50 20 -74 21 23

28' east-southeast of NGC 796. 150X: obvious, very bright, small, round hazy glow, with a size of 20". There is a 13 mag. field star off the south-western edge. In the rest of the field there is a light scatter of a few 12 mag. stars.