“There is one glory of the sun, another glory of the moon, and another glory of the stars; for one star differs from another star in glory”
(1 Corinthians 15:41, actually)

You might not have thought that a working knowledge of the King James version of the Bible comes in handy for astrophysics. But, then again, on a wet overcast night, there’s not much to see. And whether you’re of a religious persuasion or not, the authors of the King James version did have a certain beautiful turn of phrase. Also, where I live in a dark, damp and overcast part of England, fine nights aren’t too common. But at least it’s dark here. Most people don’t live in a “dark site” – they live in the middle of a town or city. Stars ? What stars?

This is where “planetarium” programs come in. You can observe the “glory of the stars” without the discomfort of actually going out and looking upward or being blinded by street lights. If you’ve got a limited time available for observing, then planning ahead and using a planetarium to figure out what you are going to look for is a good idea. And, if you really can’t go outside and look, then wandering about a virtual sky on your desktop is the only alternative.

There are several types of planetarium program around. Some are aimed at the “sky tourist” market. They can show trips to the stars – a bit like Star Trek – and interestingly, can show the change in star positions as you move at many times the speed of light to your destination. Others are what you might term “serious” and contain several large star catalogues complete with reference data. They don’t do the pretty “wow” stuff, but tend to be more useful for amateur astronomers with some decent equipment.

There are really just two main functions of a planetarium program. The first is to find an object – to locate the co-ordinates and then display some information on the star or galaxy. If the object is a galaxy or the like, most planetarium programs also let you display a nice picture. The second function is to point a telescope at the object – that is, to send commands to a motor powered telescope, such that it moves to the right position. Planetarium programs tend to have lots of fancy bells-and-whistles which can be fun to play with (precessing the equinox back to the time of the Pharaohs, for example), but these are secondary to the two above.

I’ll look at two of the serious products here, both of which control a telescope and contain large databases – SkyMap Pro 11 and TheSky 6.

SkyMap Pro 11
£69 (inc VAT), US $ 130
http://www.skymap.com

SkyMap Pro looks a bit old fashioned but is practical and easy to use

I first got hold of SkyMap Pro at version 4 (back in 1998, I think). About a year ago, I purchased version 10 and I have to say that the my first thought was how little it had changed. On the surface at any rate. The display is still the same simple projection with only the brighter stars displayed by default. Very recently, version 11 has been released – and still looks much the same.

There aren’t too many configurable options, but you can do things like selecting the magnitude of the stars to be displayed, the “shape” of stars and also their “colours”. The colour of a star as displayed in a program like SkyMap Pro can be a bit misleading; because stars are dim objects, the colour of a particular star is normally nothing like what is displayed on a computer screen. Still, it can be better than looking at white dots on a black screen.

You can zoom in and out of a particular region of sky with the magnify & reduce tools and, if you want, you can create several different map windows covering separate areas of sky - a feature that I find very useful. You can zoom in on a region of interest and then create another window covering a completely different area of sky. I find I use this a lot, as, in order to test the pointing accuracy of my telescope, I’m always going from Arcturus, say, to Vega and back again.

Of course, as with most (if not all) planetarium programs, a key feature is the ability to control a telescope with the program. With SkyMap Pro, you click on a star, select Slew and the telescope will move to the required coordinates. If your telescope is properly aligned and the control system corrects for various other factors, the star or other celestial object should appear in the eyepiece. SkyMap Pro does correct for astronomical variations such as precession, nutation and aberration but it doesn’t correct for telescope errors.

One of the things that you’ll find early on in using any planetarium program, is that using it on a desktop and using in the dark in the middle of a field are somewhat different things. My experience of “field work” is that if something can go wrong it will. Anything from simply falling over a wire to finding the cat asleep in the optical tube assembly. This is where SkyMap Pro scores. It’s easy to switch view from North to South to Zenith for example, and easy to zoom in. The toolbars have nice big button logos so that moving around at night is pretty easy to do.

In version 10, the thing I didn’t particularly like was that it seemed hard to find objects. Take for example trying to find the quasar 3C 273. You pressed Alt+D (SkyMap Pro has nice shortcuts, incidentally) and got a dialog box which asked you to enter the name. Entering “3C373” failed: you had to enter “3C 373” (with a gap). In version 11, it all works smoothly.

The dialog boxes in SkyMapPro would probably have been familiar to users of Window 3.1. On the plus side, they are big and clear.

A minor niggle is how SkyMap Pro handles daylight saving. I personally detest daylight saving. I don’t particularly see why I should be inconvenienced for the sake of a few farmers in the north of Scotland. But I have to put up with it and I expect not to be further troubled by programs that expect me to enter details about daylight saving. Windows knows about this sort of thing: when you install Windows, you enter a time zone and forget about it thereafter. A program can get information about time zones, daylight saving and even accurate atomic time server data from Windows. But SkyMap Pro doesn’t – you have to enter it manually.

When I commented earlier about version 4 being rather similar in outward appearance to version 10, I think I got near to what bothers me about SkyMap. There are no “modern” features like tree views or property panels that I could find. It reminds me of Windows 98. While it works perfectly well, it has a dusty feel to it, somehow.

TheSky 6, Serious Astronomer Edition
US $129; £69 (inc VAT) - widely available
http://www.bisque.com

TheSky has a well organised and up-to-date user interface

TheSky is a full featured planetarium program that comes in several editions. The Student Edition has maps and the basic display functionality, but it leaves out the all important telescope control. The intermediate level Serious Astronomer Edition does have telescope control and several other interesting features such as multiple projections and a database query wizard. The top level Professional has several more bells and whistles mainly aimed at integrating with Bisque’s other products such a its Paramount equatorial mount. The version I’ve got is the Serious Astronomer Edition.

The first thing to say about TheSky is that it has more options, features and other gizmos than you could reasonably want. And that’s one of the problems with it: it can be complicated to set up in exactly the way you’d like. There’s a Display Explorer which nicely organises just about every visible blob or line that you can display into a tree structure – and lets you determine how it should be displayed. So if, for example, the meridian line is something that’s of particular interest, you can set it to display as a bright green line, 5 pixels wide. And so on for about 40 to 50 different display items.

Telescope control is performed in a similar way to SkyMap Pro, but you get several more options when you right click on the screen with the mouse. There’s also the nice feature of a small panel appearing while the telescope is moving that allows you to abort the slew if you need to in a hurry. An (expensive) add on is TPoint – software for correcting the deficiencies of an equatorial or fork mount. I haven’t tried this, but I know from having written and used similar software that it really does improve the pointing accuracy of your telescope.

One potentially useful feature is the Data Wizard. This allows you to interrogate TheSky’s databases to find out a list of objects of interest. In theory, you should be able to produce a list of double stars brighter than magnitude 6, say, and with a separation greater than 2 arc-seconds. When I tried this, it didn’t work too well. I was looking for a set of double stars with separations between 2 and 4 arc seconds to use as test stars – but the search missed out at least one – Izar. I suspect that the problem here isn’t so much with the Data Wizard, but with the way astronomical databases are constructed. Unlike SkyMap, the data catalogues “open up” into tree views, so that you can find “3C 273”, say, without having to type it in.

TheSky uses modern TreeView controls, but the downside is that clicking on a small cross at night while wearing gloves can be a bit tricky.

Another feature that I particularly liked was the ability to select a different style of projection. Most of the time you want something like a stereographic map. But on occasion you may want another type of map such as an Orthographic projection, which I find useful as it gives more weight to objects high in altitude and squashes low altitude objects up. In practice, there are few things to see low in the atmosphere.

TheSky 6 has a nice “modern” feel to it. Everything is logically organised and well thought out. But in a field, by a telescope, I have found it consistently more difficult to use than SkyMap. I can’t put this down to any one thing apart from the sheer number of options available in TheSky. It’s quite possible to select an option you didn’t want and spend some time figuring how to get back to where you need to be. In the dark, under the stars, “keep it simple” is the watchword.

Conclusion

Both products serve the purpose intended: to locate objects in the sky, display information about them and point a telescope at roughly the right area. TheSky looks nicer than SkyMap Pro – but that’s a highly subjective view. No doubt, some will find SkyMap Pro better looking. In practice, though, I have found SkyMap Pro easier to use, probably because it has fewer options and slightly larger buttons. In a field on a dark night that’s a plus. I find I use it more than any other planetarium program.

Dermot Hogan

June 2005