About NightSky
NightSky is a RISC OS compliant application which generates star maps on any scale and as seen from anywhere on earth and at any past, present or future date and time. Because of the processing power and speed of the Acorn family of Rise OS computers, the calculations of positions of the sun, moon and planets can be biased in favour of accuracy rather than speed, so that realistic views of events such as eclipses of the sun and moon, occultations of stars by the moon and transits of Venus and Mercury can be obtained. Even so no whole or part sky view ever takes more than a few seconds to construct.
NightSky is intended to accompany and to encourage active observation of the heavens, if possible using binoculars or a small telescope. It features
- Whole or part-sky view of the heavens at any place on earth and any time displayed in seconds. You can edit the file of places, and create new ones. You can control which stars and planets will be labelled, and add more annotations of your own after the map is drawn.
- A large database of stars, held in memory for processing speed. There is a (present) maximum of 26,104 stars down to magnitude 7.55; this is three times fainter than the faintest star that can ever be seen by an unaided eye. This maximum catalogue requires 500K of memory, but does not have to be loaded in full. The minimum catalogue is 2704 stars down to magnitude 5.4, needing only 52K of memory.
- Computation of the positions of sun, moon and planets that allows demonstration of solar eclipses and lunar occultations with errors in space of no more than a few kilometres on the earth's surface and, typically, a couple of minutes in time. A facility to generate a file of predictions (or ephemeris) of occultations for any particular place is provided.
- Comprehensive identification and finding routines for any object.
- Tagging of any object and storage of notes on it. A few hundred interesting stars and Deep Sky Objects (star clusters, nebulae and galaxies external to our own Milky Way) arc tagged already, and you can read and edit (or delete) the notes on these. Most of these objects are double stars that can be observed as such with modest equipment.
- Demonstration of changes in the sky over long periods of time due to Precession of the equinoxes, and the Proper Motions through space of the stars themselves.
- Comprehensive saving routines. Maps may be saved to disc or other applications as sprite or draw files. Much more economically, the parameters necessary for NightSky itself to re-create the map in a few seconds can be saved in a special file of standard format. You can construct sequences of linked maps that will be generated automatically. In this way you might show the changes in the sky at a particular place over the course of a year; or the progress of an eclipse or occultation.
- RealTime facility. You can arrange to have the map refreshed after a set delay with an interval between maps that can range from one minute in normal real-time mode to 10000 years, for study of how constellation shapes change due to the real motion of the stars through space.
- Customisation. You have complete control over the operation of NightSky and can arrange for it to operate as you wish. This covers matters such as the default place initially selected; type of plot; faintest stars considered; which stars if any are labelled with proper names and/or their constellation IDs; fonts selected for all labelling activities; and all colours used. You do not have to trouble yourself with these technicalities, of course. Two sensible default sets of parameters are stored within NightSky, one appropriate to coloured maps on-screen and the other to monochrome hard copy for your printer. All of this means that having installed NightSky on the icon bar you can examine the state of the sky "here and now" with a single choice from the main menu, a total of two mouse clicks.
Conventions used in this guide
We use the standard Acorn conventions for the mouse buttons:
- SELECT is the left button, and the most commonly used.
- MENU is the middle button and is usually for opening menus.
- ADJUST is the right mouse button.
Unless otherwise stated Choose means move over something and click on it with SELECT or ADJUST .
Error or message dialogue boxes may appear from time to time. They contain action icons with labels that vary with context, for instance SAVE, QUIT, cancel. This would appear if you tried to quit NightSky when the file of places in memory had been altered but not saved. In such a case SAVE would cause the standard dialogue box to appear to allow your work to be stored on disc, QUIT would do just that, losing the new information, whilst cancel would abort the exit procedure.
It is assumed that you have read the Welcome Guide supplied with your computer and are familiar with the RISC OS Desktop environment
Animations.
This term is used to refer to a series of screens calculated in real-time by NightSky. There is so much calculation to do that true animation is not attainable, though use could certainly be made of NightSky images in movie-making applications. NightSky animations will be smooth and flicker-free provided adequate screen memory is available.