The number of visible objects in a telescope is at the very least an imposing task. How will all these objects be found? Long hours of practice will of course allow each one to refine their own techniques and thanks to the use of charts and a good researcher this task is made easier. This method, " star-hopping " or also known as visual advance is not the only solution currently offered to the observer.

In recent years there has appeared the digital circles of co-ordinates. These first units only indicated the position pointed by the instrument. Technical advances have now included the ability to use huge databases of objects. In 1994, I decided to equip my old 406mm with a similar system. After some research, I chose the model suggested by Victor McKeighan: SkyCommander(tm). The base unit has a list of 9000 objects, its price was $390, that is to say a little more than 3200FF T.T.C. using the current exchange rate of one dollar to 6FF. Victor often goes to Winter Star Party (to Florida) and its product seems very appreciated US amateurs. The package includes an understandable operation manual, the computer, the cables and both coders with the parts necessary to the their installation. The design of the 406 mm Dob had not envisioned the addition of encoders but these modifications were easily done. On the other hand, my new 560mm had been built with a very low profile and consequently the azimuth coder (of 42mm thickness) is right under the passage of the primary mirror. It was necessary only to relieve a space in order to have an adequate margin of clearance to allow the unit to be removed. One can also integrate it into the ‘scope design and leave it permanently. This coder is fixed on the pre-bored pivot of the base. The axis of the coder of altitude is centered and fixed on one of the pivots of the telescope. My current instrument has a virtual “pivot center” and so required the fabrication of an attachment arm to locate the coder.

The principle of operation is relatively simple. The azimuth coder and the altitude coder send their information via the cables to SkyCommander. At the beginning of the night the procedure consists in fixing the coder of altitude. The azimuth remains in place as it is well protected, then to connect these to the computer using the cables. The initialization procedure is as follows:

1 - Powering of SkyCommander

2 - Entry of the current date (necessary to determine the position of planets)

3 - Centering of the telescope on a first star (catalogues of 40 brilliant stars)

4 - Centering on a second star also in the catalogue.

Two types of co-ordinates are available, Altitude and azimuth, which is appropriate for a Dobsonian design or a read out showing right accession and declination (more practical in the case of an equatorial mounting).

The use in alt/azimuth mode is simpler:

1 Choose the catalogue of the objects

2 Choose the number in the catalogue, NGC, IC, etc….

3 The angle then appears which separates the ‘scope from the object

4 One then moves the instrument until the display indicates 000.00 in altitude and 000.00 for the azimuth. Arrows indicate the direction of rotation to be carried out by the operator in order to know which way to go. More complex to describe than to realize in use, these procedures quickly become an automatic reflex and in a few tens of minutes are enough to control the functions necessary to effectively use SkyCommander. The buttons are very practical and usable while wearing gloves. The green-lit display has an adjustment of intensity in order to protect night vision. One can also save the initialization procedure, using the mode "day before”. The standard 9V battery will allow saving this for approximately 30 to 40 hours. This feature allows one not to have to realign the instrument again within this time frame. A simple pressure on one of keys and the computer is reactivated. In order not to fall into what is called "dry breakdown", the duration remaining of the initialization procedure is posted in the form of bars to show time remaining.

While using Sky Commander, it is a pleasure to simply choose an object and then, after some movements of the instrument, have it centered within the eyepiece field. A firm ground, a careful alignment and a good ‘scope assembly appreciably improve the precision of pointing.

Objects available in the database thus contain a selection of 9000 objects and their descriptions (Magnitude and type; not always reliable). Certain lapses of memory are surprising (NGC 4676 for example), and if an object need further description, it is possible to add a personal impression in the catalogue or add to it a new comet of the night.

The extracts come from the following catalogues: Messier, Ngc, Ic, Ugc, Collinder, Trumpler, Berkeley, Barnard, Melotte, planets, 600 stars double (SAC), and your own personal catalogue. There is a possible connection with Guide as well as other software (in particular to download co-ordinates via the optional port series), but not having a PC on the ground I have not been able yet to test that.

Various functions:

A very useful function is the ability for realignment and identification. When a weak object is sought, it is possible to refine the units pointing accuracy on a close object that is clearly identified, then perfectly to center the co-ordinates (000.00 - 000.00) of a remote object to know for sure what is centered in the eyepiece. Another useful function, the mode "Search" unceasingly displays on the screen all the possible name of the objects that pass in the field of the eyepiece.

The database can also be consulted by constellation, SkyCommander proposing different NP or other clusters available. In order to limit this type of search, it is possible to indicate the weakness from the magnitude not to be exceeded. One function available too was planned for the use of an equatorial table in order to avoid the realignment of the computer with each resetting of the platform.

Use:

While in use SkyCommander gives me complete satisfaction. Admittedly, the charm of charts with a weak light held between the lips disappears but comfort while observing is the aim. It is preferable to draw up a list of the objects to be observed and to carry out a true tourist route hopping from one item to the next. Serviceable time for the observation increases clearly and does not involve any frustration when the objects sought after are extremely faint and at the limit of perception. One minute is sufficient for to find the majority of the targets and after 4 years of use, it would be difficult for me not to use this system.

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