Astronomy on your own Computer – where it all began

Sometimes, you just need luck. For quite a while now, I have been looking for an old computer program called Skyplot. Next to some very cold nights out under a clear Bavarian sky back in 1985, this is probably what sparked my initial interest in the skies above – and although I did not touch a Schneider CPC Computer for more than 30 years, I never forgot about Skyplot.

The program is rare – I found some people on the Classic Computer Forum and they rendered some help (including the offer to send a copy over on a 3″ Disk) but I was after the original listing (or at least a scan thereof). And then I bought ZX81 Magazine on eBay. And it just crossed my mind to see what else the seller had on sale – a couple of CPC Magazines along. And then, there was a copy of a magazine from Austria – released in January 1987… I took a look… and there it was… right on the cover!

From the Magazine to the PC…

I have written about getting the code from the magazine into the system using Scanning, OCR and Notepad++ – I am not going to repeat the story here. I placed the initial, uncleaned text file right in Subversion to have a baseline in case anything goes wrong and started cleaning the code in Notepad++.

Code 01 - Uncleaned VersionYou may already be able to pick up some of the more obvious problem areas:

  • Percent-Characters (“%”) have not been OCR-ed properly…
  • Spaces (” “) in places they should not be in…
  • Ampersand-Characters (“&”) not properly OCR-ed…
  • The number “1” and the character “l” are not properly OCR-ed which is extremely difficult to see in the result… and so are the number “0” and the character “O”.

… and into the CPC Emulator

So here we are – the code is in the PC, possibly written using a tool like Notepad++ and has been reviewed and corrected. Now what?

With a little bit of help from the author, I managed to use JavaCPC Version 2.2b and it’s AutopType feature to get the code over – important hint was to use the “As BASIC” option. Paste the code into the AutoType window, select the “As BASIC” option and hit the Send to CPC button. It will take a while but it will bring your code into the emulated CPC.

JavaCPC 01 - AutoType as BASICOnce the auto-typing feature is done (after a few minutes for a listing of this size) we are able to use the emulated CPC and look at the first line of code within. For a better overview, I have switched to MODE 2.

JavaCPC 02 - The CodeNow, some 28 years after it has been published, the cleaned and imported code (hopefully) runs again.

Skyplot 01 - Main MenuI have left the program in German as this is the original language it was published in. Just for a quick functional check I will ask Skyplot to draw us a map of the stars today, Thursday, October 3rd, 2013.

Skyplot 02 - Full Map of the SkyBut I am more curios about the exactness of the calculations of a software almost 30 years old – so the next thing to ask for is a map of the visible sky for November 15th, 2013 at 22:00 local time for 50°N.

Skyplot 03 - Visible Sky mid NovemberA comparison with astronomical literature reveals: spot-on! Except, of course, two objects that have been of interest when Skyplot was published in the mid 1980s – but not today: Pluto can still be seen among the planets and Comet Halley is also on the screen – of course, not visible today…

And – if you look closely: there is a bug somewhere 😉 – but I’ll leave that for the next session…

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