
This program is to be distributed free of charge.
If you alter the code then distribute it, you have to provide the new code.

ORRERY is an animated model of the Solar system, running on the OmniGo 100 and Ensemble.
For some reason, the IZL interpreter rejects it under NDO.

It lets you examine the nine planets as they appear tonight or thousands of years in the past or future.
Move backward/forward in time in steps of days, weeks, months or years.

Use it to decide when will Mars be close to us again or, what's that "May 2000 planetary lineup"
all about. Or would you like to see where the planets were when Galileo first aimed his telescope
at Jupiter? Where was Pluto when Tombaugh discovered it in the 30's? 
Many discoveries are waiting for you !

Files in this distribution:
ORRERY.TXT	this file
ORRERY.IZL	the source
ORRERY.IZT	token file
ORRERYOG.PCX	OmniGo 100 screenprint of the All planets view
ORRERYEN.PCX	Ensemble screenshot of the Outer planets view
ORR_PROG.TXT	programmer's notes

To install, simply copy the ORRERY.IZL and/or ORRERY.IZT file in your Document directory.
Note that the IZT contains the full directory path. The supplied ORRERY.IZT contains B:\GEOWORKS\DOCUMENT
If you intend to put it on a RAM card, change the B: to E: with a hex editor or load the IZL
(takes over a minute on the OG) and use the 'Save token file' IZT function.


To show the graphics, I am overlaying IZL's labels for F1 and F2.
They still work, only not with the stylus.

This version supercedes version 1. It has the following improvements:
 -Separate views for all/ inner/ outer planet display, to allow correct scale of orbits.
 -Explanation screen for each view
 -Highlights Earth's orbit
 -Displays no Sun, but shows Mars on Outer planets display for comparison
 -Detailed error messages from date check
 -Run function won't go beyond 1/1/4712 B.C. in Bwd Step mode
 -Settings dialog boxed


BACKGROUND INFORMATION
======================

Orrery was the name given to the early, clockwork-driven solar system models.

This program offers three views. Each has a short note screen, activated by the Explanation
button.

On the Settings screen, the "Day" and the "Increment by" values accept fractions.

To see all nine planets, choose All planets.
On this view, orbits are represented by concentric circles at uniformly increasing
distances from the Sun in the centre.

This is a simplification: in reality, the planets do not orbit the Sun in concentric
circles, but ellipses and their distance from the Sun is many times that of the Eart-Sun distance.
The other views show orbits proportional in their size and position.

To only see Mercury, Venus, Earth and Mars, choose Inner planets.
To only see Jupiter, Saturn, Neptune, Uranus and Pluto, choose Outer planets.


On the right hand side of the display, you will see the current date in yyyy.mm.dd format.
This is followed by the Julian date as used in astronomy - its starting date is Jan 1.4712 B.C.

Under this is the time-step you chose in Settings. Use the 'Bwd step' and 'Fwd step' buttons
to move back and forth in time. Press the 'Run' button to have Orrery step coninually in the
last step direction until stopped (the buttton face changes to 'Stop' once 'Run' is activated).

The planets' position is given by their longitude as measured around the Sun.
This is an angle, measured from the point where the Sun appears in the sky on March 21st
each year (known as the Vernal Equinox or First point of Aries).

On the displays a line running towards the 3 o'clock position indicates this point.


If you already know about astronomy
===================================
You may want to use ORRERY.IZL to easily visualise, confirm or predict the visibility of planets:
- conjunction, opposition
- evening or morning event?
- approximate position in the sky (from heliocentric longitude
- approximate rise/set time (from angular distance to Sun
- inferior planets- approximate date of maximum elongation
- superior planets- approximate date of start and end of appearences
- all planets- approximate angular size (say, about max size or halfway between max and min


Send feedback (please!) or bug reports (sigh) to:
cynpet@netspace.net.au

Enjoy!

Peter Eros
