

                            SkyView User Guide
                            ------------------


Contents
--------

 1. Introduction

 2. Getting Started

 3. Using SkyView
     3.1  The Graphical Display from SkyView
     3.2  Symbols
     3.3  Getting information on a displayed object
     3.4  Search facilities: 'Selecting' an object
     3.5  Printing
     3.6  Speed and accuracy

 4. The Main Menu
     4.1  Program info
     4.2  Observer...
     4.3  Display ->
     4.4  Horizontal view
     4.5  Vertical view
     4.6  Print ->
     4.7  Select object ->
     4.8  See selection ->
     4.9  Selection info
     4.10 Cancel selection
     4.11 Quit

 5. Types of object present in SkyView
     5.1  The Sun
     5.2  The Moon
     5.3  Planets
     5.4  Stars
     5.5  Markers
     5.6  TV Satellites (geostationary)
     5.7  User object

 6. Bibliography



1. Introduction
---------------

The aim of SkyView is to provide an easy-to-use, informative sky simulation
which is of interest to the naked-eye astronomer.

The program is used as follows.  The user enters a date & time and a
location on the Earth's surface, and SkyView then calculates the
position of various celestial objects as they would be seen from there
at that time.  The result is displayed graphically in scrollable
windows.

The user can obtain information on any displayed object by clicking on it.
In addition, the program can search for any of the objects it knows,
and then bring that object into view or show it at rising, setting or
culminating.

The list of objects included in the current version of SkyView is:
  - The Sun
  - The Moon
  - All eight planets
  - All stars of magnitude 4.0 or brighter (plus some dimmer ones which
    help to make constellations more recognisable)
  - Artificial markers at regular intervals of Right Ascension and
    Declination
  - TV satellites (purely out of interest!)
  - A general purpose 'User object' at a Right Ascension and Declination
    specified by the user.
The display of any type of object can be switched on or off at any time.

There are facilities to generate hard copy (via RISC OS printer drivers),
and to set a default location and observation time which are automatically
loaded on startup.

The program is WIMP-based and multi-tasking, and runs in a 320K Wimp Slot.
The display benefits significantly from the high resolution of the
multisync modes, but lower resolution modes can also be used.



2. Getting Started
------------------

This section sets out the basics of getting the program going.  A more
detailed explanation of all menu options and dialogue boxes is given later
in the Guide.

SkyView can be run directly from floppy disk, or alternatively it can be
copied to a hard disk and run from there.

To run SkyView, double click on its icon in a directory viewer.  After a
few seconds, the program's icon appears on the icon bar.  Click 'Menu'
over the icon to bring up the main menu.  Most of the menu items are
greyed out at this stage, because the time and location of observation
have not yet been set.  Choose the 'Observer...' option to cause the
'Observer details' dialogue box to appear, and click on the up and down
arrows until the display shows the location, date and time required.
You may need the following buttons as well:
   The 'N/S' button toggles between North & South latitude;
   The 'E/W' button toggles between East & West longitude;
   The 'C'   button toggles between the 20th and the 21st centuries.
The 'Time offset' field tells SkyView what time zone the 'Time' field
represents.  For example, if you wish to use British Summer Time (one hour
ahead of GMT) throughout the program, set this field to +1.0.

Once you are happy with the settings, click on 'OK'.  Finally, click 'Menu'
over the SkyView icon to recover the main menu (now with most options
available), and choose one or both of 'Horizontal view' or 'Vertical view'
to display the program's graphical output windows.  All the facilities of
SkyView, described in detail below, are now available.

Hint: If you click on the 'OK' button with Adjust instead of Select, the
dialogue box remains on screen.  You can then recover the main menu by
clicking Menu anywhere within the dialogue box.



3. Using SkyView
----------------

3.1 The Graphical Display from SkyView

SkyView uses two WIMP windows to display its output.  The Horizontal
window displays all parts of the sky from the horizon to sixty degrees
above the horizon, while the Vertical window displays from sixty degrees
to directly overhead.  They can be open at the same time.

The horizontal line near the bottom of the Horizontal window represents
the observer's horizon.  Compass directions are marked at intervals
below this line.  As a Mode 12 or 20 screen is only wide enough to show
ninety degrees of azimuth (two compass octants) at a time, the window can
be scrolled smoothly from side to side to show the required part of the
sky.  To prevent the left and right boundaries of the window from getting
in the way, the compass direction appearing at the centre of the window
can be set using the 'Direction' buttons in the 'Observer details'
dialogue box.

The middle of the Vertical window corresponds to the observer's zenith,
and the compass circle is plotted at just below sixty degrees of altitude.
The compass direction at the six o'clock position is the same as the one
at the centre of the Horizontal window.

There is a small amount of overlap between the areas covered by the
Horizontal and Vertical windows, so an object near sixty degrees of
altitude can appear in both windows.


3.2 Symbols

The types of object present in SkyView are represented by the following
symbols:
                                                            Default
 Object             Symbol                               Display State

 Sun             Large yellow dot.                            On
 Moon            White circle. Extent of white                On
                 filling indicates phase.
 Planets         Blue dot with vertical blue line.            On
 Stars           Grey dot. Size and brightness indicate       On
                 brightness (magnitude) of star.
 Markers         Green cross.                                 Off
 TV satellites   Red dot with diagonal red lines.             Off
 User object     White cross.                                 Off

The display of any type of object can be turned on or off at any time,
using the main menu option 'Display ->' (see Section 4.3).

More details of each type of object are given in Section 5.


3.3 Getting information on a displayed object

Information on any displayed object can be obtained simply by clicking on
it (using the left hand mouse button).  SkyView will then show the
'Information on object' dialogue box, which contains information
appropriate to the type of object clicked on.  For example, if the object
is a star, SkyView gives data such as the constellation name, the star's
identifier (Bayer letter or Flamsteed number), the visual magnitude, and
the Right Ascension and Declination.  Full details of the information
given for each type of object are set out in Section 5.

There can sometimes be several objects on top of each other.  If this
happens, the panel near the top of the 'Information on object' dialogue
box indicates that it is currently showing the information for the nth
object (where n is the number of overlapping objects), and the up and
down arrows next to the panel can be used to cycle through the objects.
These arrows are greyed out when there is only one object.

The 'OK' button in the dialogue box closes the box.  The 'Select' button
is one way of 'selecting' the object - see the next paragraph for an
explanation of this.


3.4 Search facilities: 'Selecting' an object

Any one of the objects known to SkyView can be 'selected' (even if that
object is not currently on display).  Special treatment is given to the
selected object, as follows:
  - Whenever it appears in a display window, it is surrounded by a
    small rectangular frame.
  - If the object is currently above the horizon, SkyView can
    automatically rearrange the display windows to bring it on screen.
  - SkyView can automatically adjust the time of observation to show
    the selected object at the time of rising, setting or culminating.
  - Information on the selected object (including the times of rising,
    setting and culminating) is always available, even when the object
    is below the horizon.

Objects are selected via an option on the main menu (see Section 4.7 of
this Guide) or via the 'Select' button in the 'Information on object'
dialogue box (as described above).
                                  
Once an object has been selected, the facilities for bringing it into view
and obtaining information on it are available via main menu options (see
Sections 4.8 - 4.10).


3.5 Printing

The current central quadrant of the Horizontal window, and the complete
Vertical window, can be printed out via RISC OS printer drivers.  The
grey scale is automatically inverted for printing, to avoid solid black
backgrounds.  A title summarising the location, date and time of the
observation is included.

To print, use the main menu option 'Print ->'.  This is described in
Section 4.6 below.


3.6 Speed and accuracy

Running on an A540, SkyView takes 3 - 4 seconds (depending on screen
mode) to calculate a complete celestial hemisphere with all types of
object enabled.

No guarantees of accuracy are given!  However, in random checks with
a 1990 Astronomical Almanac, the positions of the planets examined were
typically found to be correct to within a few minutes of arc in Right
Ascension and Declination.  Similar results have been obtained for other
types of object.

At present, none of the calculations allow for effects such as the
proper motion of stars, precession, nutation or atmospheric refraction.



4. The Main Menu
----------------

The main menu can always be brought up by clicking 'Menu' over either
of the display windows, or over the SkyView icon on the icon bar.
Most of the program's facilities are accessed via this menu.

The options on the main menu are detailed below:


4.1 Program info

This displays a dialogue box containing the usual information about the
program (including version number).


4.2 Observer...

Choosing this option brings up the 'Observer details' dialogue box.  The
settings on display are the ones currently in effect in the program.

The main features of the dialogue box were described in Section 2
('Getting started').  The remaining features are as follows:

The 'Direction' radio buttons:
These set the compass direction which appears at the centre of the
Horizontal window and at the six o'clock position in the Vertical window.

The 'OK' button:
Clicking on this button puts the settings on display into effect.  If you
click with 'Adjust' instead of 'Select', the dialogue box remains on
screen.

The 'Cancel' button:
Clicking on this with 'Select' closes the dialogue box without making
any changes.  If you click with 'Adjust', the box remains on screen and
the settings on display revert to the ones currently in effect in the
program.

The 'Defaults' buttons:
The 'Set' button causes the settings currently on display in the
dialogue box to be saved to disc as the start-up defaults.  The dialogue
box normally then closes automatically, but it will stay open if you
click with 'Adjust'.
The 'Show' button causes the dialogue box to be loaded with the current
default settings.  Note that the settings actually in effect in the
program are not affected until you click on 'OK'.

The 'Sys date' button:
This causes the current date (as read from the system clock) to be written
into the Year, Month and Day fields.

Other notes:
SkyView ensures that the date on display is always valid.  To avoid
confusion, it is a good idea to set the Year and Month fields before
setting the Day field.
It is not possible to observe from either of the Poles.
Clicking 'Menu' anywhere within the 'Observer details' dialogue box brings
up the main menu.


4.3 Display ->

This is used to set the display options for the types of object present in
SkyView.

Follow the right-pointing arrow to bring up the 'Display:' sub-menu.
Choosing any item in this sub-menu toggles the display of the corresponding
object type on and off (a tick indicates that display is currently on).

If you turn off the display of the selected object (see Section 3.4), the
selection is automatically cancelled.

Some types of object have additional display options, accessed via lower
levels of sub-menus or dialogue boxes.  These are described in Section 5.


4.4 Horizontal view

Choosing this item toggles the Horizontal window between being open and
being closed.  A tick indicates that the window is currently open.


4.5 Vertical view

This does the same for the Vertical window.


4.6 Print ->

Follow the arrow to bring up the 'Print:' sub-menu.

The 'Horiz. quadrant' item prints the central quadrant of the Horizontal
window via the RISC OS printer driver currently installed.  Note that this
quadrant is not necessarily the one currently on the screen.  Use the
'Direction' radio buttons in the 'Observer details' dialogue box to
determine which quadrant gets printed.

The 'Vert. complete' item prints the complete Vertical window.

In both cases, the grey scale is inverted to avoid solid black backgrounds.
The size of the printed image is optimised for A4 paper, but will also fit
on a print area 8.5" wide by 11" high.


4.7 Select object ->

Follow the arrow to bring up the 'Select:' sub-menu, which is used to
'select' a specified object (see Section 3.4).  The exact method depends
on the type of object - details are given in Section 5.

The menu entry for a type of object is greyed out if the display of that
type of object is currently switched off.

Selecting an object automatically cancels any pre-existing selection.


4.8 See selection ->

Follow the arrow to bring up the 'See selection:' sub-menu.  Choosing
one of the items in this sub-menu causes SkyView to adjust the windows
(and, if necessary, the time of observation) to show the selected object
now, on rising, on setting or on culminating.  To guarantee that the
object is immediately visible on screen, the Horizontal window should be
set to maximum height and the Vertical to maximum size.

The 'Now' item is greyed out if the object is not currently above the
horizon.  The 'On rising', 'On setting' and 'On culminating' items are
greyed out if the selected object does not rise or set or culminate
(respectively) on the date currently set.

If there is currently no selected object, all the options are greyed out.


4.9 Selection info

This item displays information on the selected object, even if the object
is not currently visible.  The times of rising, setting and culminating
are included.  The 'OK' button simply closesthe dialogue box.

This menu item is greyed out if there is currently no selected object.


4.10 Cancel selection

This item cancels the current selection.  If there is currently no
selection, the item is greyed out.


4.11 Quit

Choosing this item quits the program.



5. Types of object present in SkyView
-------------------------------------

This Section describes each type of object in detail, including any
special display options and how to select an object of that type.

The 'Display:' sub-menu mentioned in this Section is brought up by
following the arrow on the 'Display ->' item in the main menu.  Likewise,
the 'Select:' sub-menu is brought up via the 'Select ->' main menu item.


5.1 The Sun

Symbol:
A large yellow dot.

Display options:
Choose the item 'The Sun' in the 'Display:' sub-menu to toggle the display
of the Sun on and off.

Information available:
Current Right Ascension and Declination.

Selecting:
Choose the item 'The Sun' in the 'Select:' sub-menu.


5.2 The Moon

Symbol:
A white circle.  The extent of the white filling of the circle indicates
the phase, as follows:
      Open circle..............................Near New Moon.
      Right half filled, left half open........Near first quarter.
      Filled circle............................Near full moon.
      Right half open, left half filled........Near third quarter.

Note that these symbols are NOT intended to represent the true size or
orientation of the illuminated crescent.

Display options:
Choose the item 'The Moon' in the 'Display:' sub-menu to toggle the
display of the Moon on and off.

Information available:
Approx age (days since New Moon).
Current Right Ascension and Declination.

Selecting:
Choose the item 'The Moon' in the 'Select:' sub-menu.


5.3 Planets

Symbol:
Blue dot with vertical blue line.

Display options:
Choose the item 'Planets' in the 'Display:' sub-menu to toggle the
display of all planets on and off.

Information available:
Name of planet.
Approx visual magnitude.
Distance from Earth (astronomical units).
Phase (0.0 = new, 1.0 = full).
Angular diameter (seconds of arc).
Current Right Ascension and Declination.

Selecting:
Follow the right-pointing arrow on the 'Planet ->' item in the 'Select:'
sub-menu.  Then choose the planet you wish to select.


5.4 Stars

Symbol:
Grey dot.  The size and brightness of the dot indicate the magnitude of
the star - see Display Options below.

Display options:
SkyView divides the stars into eight magnitude groups, and uses a
different symbol to represent each.  The user can determine which symbol
is used for which group.  Follow the right-pointing arrow on the
'Stars ->' item in the 'Display:' sub-menu to bring up the dialogue box
entitled 'Alter Star display options'.  The magnitude groups are shown on
the left (the lower limit is inclusive, the upper exclusive) and the
corresponding symbol is shown on the right.  Click on the arrows to cycle
through the library of available symbols.  The 'up' arrow gives brighter
or larger symbols, and the 'down' arrow gives smaller or dimmer symbols.
The yellow buttons at the foot of the dialogue box work in an analogous
way to the buttons in the 'Observer details' box described in Section 4.2.

To toggle the display of all stars on and off, choose the 'Stars ->' item
itself.

Information available:
The magnitude.
The star's Flamsteed number, Bayer letter and Bright Star Catalogue number,
in that order.  One or more of these items may be absent.  (The catalogue
number is that in the 3rd revised edition of the Yale Bright Star
Catalogue.)
The name of the constellation (genitive case).
The star's proper name, if known.
The Right Ascension and Declination.

Selecting:
There are four available methods for selecting a star: by proper name, by
Bayer letter, by Flamsteed number, or by Bright Star catalogue number.
Follow the arrow on the 'Star ->' item in the 'Select:' sub-menu to bring
up the 'Select star:' sub-menu, and choose the item corresponding to the
method you wish to use.  A dialogue box appears.  Enter the requested
information (incomplete information is usually allowed, as described
below) and then click on the 'Search' button.  If a star which matches the
given details is found, its description is displayed in the dialogue box.
If this star is the one you want, click on 'OK'.  If not, click on
'Continue' to continue the search.  Repeat this if necessary until the
star you want appears, and then click on 'OK'.  Note that the 'OK' button
is greyed out if there is no star currently on offer.
Some notes on the individual selection methods now follow.

By proper name:  The case of the letters is not significant, and the name
                 can be incomplete, so 'Betelgeuse' or 'BETELGEUSE' or
                 'betel' will all find Betelgeuse.

By Bayer letter: To specify the Bayer letter, enter the name of the Greek
                 letter.  This is allowed to be incomplete, so 'alpha' or
                 'alp' will both find Alpha.  To enter a Bayer letter with
                 a superscript, type the complete name of the letter
                 followed by a space and the superscript.  For example,
                 for alpha 2 enter 'alpha 2'.  (Alternatively just enter
                 'alp' and continue the search until alpha 2 is found.)
                 To specify the constellation, enter its name in nominative
                 or genitive case, or the standard three-letter
                 abbreviation.  Again, case is not significant and names
                 can be incomplete.  For example, 'ORION' or 'Orionis'
                 or 'ORI' or 'orio' will all find Orion.

By Flamsteed No: The Flamsteed number must be entered exactly or left
                 blank.  The constellation name is entered in exactly the
                 same way as for selection by Bayer letter.

By catalogue No: The Bright Star Catalogue number must be entered
                 exactly (a blank entry is treated as 0).  There is no
                 'Continue' button in this dialogue box, as no ambiguity
                 is possible.

Other notes:     A blank entry, when allowed, will match anything.
                 The 'Search' button always begins the search at the
                 beginning of the Star database.  The 'Continue' button
                 searches from the star currently on offer, if there is
                 one; if not, it is the same as 'Search'.
                 The 'Cancel' button normally closes the dialogue box
                 without making any changes.  If clicked with 'Adjust',
                 however, it leaves the box open and resets the writable
                 icons to the values they had at the last search.


5.5 Markers

Symbol:
Green cross.

Display options:
Choose the item 'Markers' in the 'Display:' sub-menu to toggle the
display of all markers on and off.

Information available:
Right Ascension.
Declination.

Selecting:
In the present version of SkyView, the markers are generated with values
of Declination from -90 degrees to +90 degrees in 10 degree steps.  The
values of Right Ascension which are used depend on the Declination:

           Declination                     Right Ascension values
        -90 deg, +90 deg                         0 hours
         -80 to -10 deg                 0 to 22 hours in 2 hour steps
             0 deg                      0 to 23 hours in 1 hour steps
         +10 to +80 deg                 0 to 22 hours in 2 hour steps

To select a Marker, choose the 'Marker...' item in the 'Select:' sub-menu
to bring up the 'Select Marker:' dialogue box.  Click on the arrows until
the required Right Ascension and Declination are displayed, and then click
on 'OK'.  (It is a good idea to set the Declination first, as the
available Right Ascension values are different at different Declinations.)


5.6 TV Satellites (in geostationary orbits)

Symbol:
Red dot with diagonal red lines.

Display options:
Choose the 'TV sats.' item in the 'Display:' sub-menu to toggle the
display of all TV satellites on and off.

Information available:
Name.
Position.
Function (if known).

Selecting:
Follow the arrow on the 'TV sat. ->' item in the 'Select:' sub-menu to
bring up the 'TV sat.:' sub-menu.  Then choose the required satellite.


5.7 User object

Symbol:
White cross.

Display options:
To set the coordinates of the User Object, follow the arrow on the
'User obj. ->' item in the 'Display:' sub-menu.  This brings up the
dialogue box entitled 'Set details of User Object'.  Click on the up and
down arrows until the required coordinates are shown (the 'N/S' button
toggles between North and South declination), and enter a description if
you wish.  Finally, click on 'OK'.

All yellow buttons at the foot of the dialogue box operate in an analogous
way to those on the 'Observer details' dialogue box (see Section 4.2).

To toggle the display of the User Object on and off, choose the
'User obj. ->' item itself in the 'Display' sub-menu.

Information available:
Text (if any) entered by the user.
Right Ascension and Declination.

Selecting:
Choose the 'User obj.' item in the 'Select:' sub-menu.



6. Bibliography
---------------

The inspiration for SkyView came from Ronald Alpiar's remarkable
program 'Sky-Baby' for the 32K BBC Micro (see Reference 1 below).

In developing the astronomical algorithms in SkyView, I found Refs. 2 - 5
particularly useful.  Ref. 6 provided additional information and some
interesting background reading.

1. The Sky-Baby User Guide
   Ronald Alpiar

2. NAO Technical Note No. 46, "Formulae for computing astronomical data
   with hand-held calculators"
   B D Yallop
   Nautical Almanac Office
   Royal Greenwich Observatory, Madingley Road, Cambridge CB3 0EZ

3. NAO Technical Note No. 46, Section 5, "Formulae for computing
   astronomical data with hand-held calculators (Navigational Supplement)"
   B D Yallop
   Nautical Almanac Office
   Royal Greenwich Observatory, Madingley Road, Cambridge CB3 0EZ

4. The Astronomical Almanac for 1990
   HMSO
   HMSO Publications Centre, P O Box 276, London SW8 5DT

5. Astronomy with your Personal Computer (2nd edition)
   Peter Duffett-Smith
   Cambridge University Press
   ISBN 0 521 38995 X

6. Norton's 2000.0 Star Atlas and Reference Handbook (18th edition)
   Ian Ridpath (ed.)
   Longman Scientific & Technical
   ISBN 0-582-03163-X





                                                           Nigel Hawkes
                                                           1993
