Computer Star Charts

Computer star charting programs come in two different flavours: the multimedia directed ones such as

Redshift 4 and Starry Night and the observer orientated ones such as SkyMap Pro, Guide, Megastar and The Sky. Neither Redshift 4 nor Starry Night Deluxe appeared to have any double star information at all. Even if you click on a bright double star such as gamma Andromedae nothing comes up to indicate its multiple nature. These programs are more aimed at the educational market than the observers' market.

Most of the current crop of high-end computer star charting programs at the time of writing (Summer 2001) use as their base double star catalogue the 1996 version of the WDS. That is likely to change as newer releases of most of these programs are due out towards the end of 2001 and I would expect them to use the 2001 version of the WDS. The main differences between the programs are then how they allow the user to search for and display the data. Running through the four most popular star charting programs will give a flavour for how they display their data and how the search for that information proceeds. The same star, STF 1257, a double star from F.G.W. Struve's catalogue, has been chosen for all the displays.

We start with the oldest, in its current form, which is Megastar Version 4. Megastar is similar to Guide in that when you search for a double star it displays a list of discoverers and then you select the number. A typical screen is shown in Figure 23.3. The display of data is then shown in Figure 23.4. Megastar displays the least information about the star but does label the object with its correct name and has a symbol to show where the star is.

Guide Version 7.0 from Project Pluto does not appear to allow the star to have a double star symbol but it does allow the labelling of double stars with their names from the WDS. The example of STF 1257 is shown in Figure 23.5.

Unlike all the other programs Guide does allow the display of data on the chart from the Catalogue of Components of Double and Multiple Stars or CCDM. The main reason for using this catalogue is to get more accurate positions for the various components of the double stars listed in the CCDM. The CCDM is a rather strange catalogue in the information it contains and its use is mainly in improving the positional data. This was provided as an extra dataset with Guide 7. Guide also lists basic data from the CCDM. Where Guide scores over Megastar is in the information that it

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provides about the double star itself and this is illustrated in Figure 23.6.

Guide 8 also now includes the WDS 2001 edition and uses the catalogue of double star orbits as well to give information on the current PA and separation of double stars as well as animations of the stars in time showing orbital behaviour. Guide 8 also provides a user data set with the double stars from the Astronomical leagues Double star list.

The popular SkyMap Pro program in Version 7 allows the user to search for a double star through the generic star designation search facility in which the discoverer's mnemonic needs to be known first. The program then shows the double star with the standard paper chart symbol of a circle with a line through it but does not appear to allow the star to be labelled with its double star designation. SkyMap Pro also displays a large amount of information about the star including data from the CCDM and the WDS in its standard star data window, as shown in Figure 23.7.

With the appearance of SkyMap Pro 8 late in 2001 several other features of interest to double star observers have been added. These include updating the main double star catalogue to the WDS 2001, the ability

Figure 23.3. A

typical screen display from Megastar.

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Figure 23.4. Data display in Megastar.

to label double stars with their real names rather than their Tycho numbers and, perhaps most interestingly, the inclusion of the fifth catalogue of double star orbits which allows the program to compute the positions and separations for 1500 double stars whose orbits are known accurately at the current time.

The most advanced of all the sky charting programs, The Sky, version 5, level IV, from Software Bisque, is also the most limited when it comes to double stars. There is no search facility for double stars by the WDS designation. They can be queried by another stellar catalogue name if they have one. The program should mark double stars with a special symbol but also appears to display little or no information about the stars themselves. For the double star observer this program could not be recommended. The Sky for PocketPC contains no double star information at all.

The new kid on the block in star charting/logging software is SkyTools. This software is perhaps different in that in its current form, version 1.5, it allows the user to search the catalogues if you know the name of a double star from another catalogue and it will display an impressive amount of information. A user downloadable file will give you the cross-reference from the

Figure 23.5 (above). An example from Guide Version 7. Figure 23.6 (below). An example of data displayed in Guide Version 7.

Figure 23.7. An example from SkyMap pro.

Figure 23.7. An example from SkyMap pro.

WDS to one of the catalogues that SkyTools will display, normally an HD number. The base double star catalogue in SkyTools is also different being, unusually, the CCDM supplemented with double star data from Hipparcos. SkyTools is also unusual in that it has many different charts that can be plotted but on none of them as far as I could see did the selected double star have a symbol to indicate that it was a double, nor did there seem to be a way of labelling the star with its ID.

Despite the fact that the information is available in the catalogues it is disappointing that none of the programs plot the double star symbol in the way that the Millennium Star Atlas does with a line indicating the Position angle and its length giving the separation at its last measured epoch. With the exception of The Sky all the programs do something different for the double star observer and a choice of which one to use may come down to the other facilities offered.

Uranometria 2000 (2nd edition) has come out since the main body of the text was written and its double star data was taken from the Hipparcos and Tycho catalogues using PAs and separations from those catalogues along with hand updates for pairs wider than 60''.

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