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SKYSHOW.ARK
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This archive contains two MBASIC programs, SKYPLOT and PLANETS, that
will plot the celestial positions of the Sun, Moon, Planets and Stars
on your CRT. They are adaptations of programs found in the book,
"Celestial BASIC", by Eric Burgess, published in 1982 by Sybex (out of
print in 1990). According to the book's cover, the programs are
intended for "the serious amateur astronomer as well as the occasional
stargazer". I fall into the latter category.
The programs in Mr. Burgess's book have versions for the Apple II and
Exidy Sorcerer computers, but use hardware-specific graphic and POKE
instructions to plot the celestial positions in video memory. The
programs for the Exidy also assume a non-standard screen size of 30
lines of 64 characters each.
I was intrigued by the illustrations in the book, and set about
adapting two of the Exidy programs for my 24 by 80 screen, using no
graphic or POKE commands, and using a function for cursor-positioning.
Actually, my Xerox 820-II PC has a Lear Siegler ADM-3A compatible CRT,
which is standard on many CP/M computers, including the Kaypros.
To adapt these programs to your computer, you just substitute (where
they differ) your terminal's escape sequences for the following string
variables:
CURON$ = cursor ON
CUROFF$ = cursor OFF
BLINK$ = cursor blink ON
BLOFF$ = cursor blink OFF
BEL$ = ring bell
CL$ = clear screen & home cursor
HOME$ = home cursor
FNAT$ = cursor-positioning function
All of these variables are found at the beginning of the programs.
Except for the CURSOR ON/OFF, CURSOR BLINK ON/OFF and CURSOR HOME
codes, the program should run on Kaypro terminals. In fact, the
CURSOR ON/OFF and BLINK ON/OFF codes are not essential to the
programs' operation and may be eliminated, if desired. You should
also look at the translation subroutine at the bottom of each program,
if you must alter the cursor-positioning code. I have retained the
line numbers from the book, to make it easier for you to check my
version against the original.
The program SKYPLOT.BAS is an adaptation of the program SKYPLA.BAS,
beginning on page 247 of the book. By omitting the skyline graphics
and moving the heading and prompts to the right side of the screen, I
was able to retain the full sky display of the original program.
The program PLANETS.BAS is an adaptation of the program PLNTA.BAS,
beginning on page 268 of the book. I moved the prompts to the right
side of the screen for clarity, but I wasn't able to squeeze 30 lines
into 24, so I merely dropped off the bottom 6 lines of the charts.
Everything else is retained, but a few stars and the entire
constellations of Sirius, Corvus, Sagittarius, Scorpio, Fomalhaut and
Capricornus were lost with these 6 lines. Except for this, the
program operates identically to the original.
Neither of the programs is bug-free, but I have done the tedious
typing and translation job--I leave the fine tuning to anyone who is
interested.
There are 24 other useful programs in the book to transcribe, most of
which are far shorter and less complicated than the two included here.
If you have an Apple II or an Exidy Sorcerer computer, you will find
programs that require no translation; you merely have to type them in
and enjoy.
When running the programs, I suggest that you refer to Mr. Burgess's
book (try the library) for details of what the programs expect as
input, and then to be patient. On my 4 Mhz Z80 it takes a little over
3 minutes for SKYPLOT to compute the celestial positions and display
the results. Just enter the required input when prompted, and then
sit back and watch the stars come out.
Have fun.
Ernest Helliwell : 22 OCT 1990 : San Francisco, CA