Introduction

About 7 pm on Sunday 25th September 1983, seeking a well earned break from the typewriter and this book, I wondered if the planet Jupiter was visible in the clear dusk skies. The planet was already low in the southwest when I had last seen it some weeks previously, and the situation would not improve. Speed was of the essence. A quick run through of programs (as contained in this book) was called for.

First the tape of the Planetary Ephemeris program was RUN with the INPUT date of  “1983:9:25”. Barely 20 seconds later the computation was complete and a COPY made to the ZX printer of all the planetary positions.

Next the Startracker program was RUN with Jupiter’s location at RA 16h 15m and Dec – 20.8° entered, together with my latitude (+ 51.2° N). The program was stopped during the PLOTting at 18.00hr GMT (equal to 7 pm BST) and another COPY made. This COPY indicated that Jupiter would be at an azimuth bearing of 211 ° (south-southwest direction) and at an altitude of +12° above the horizon. There was still a chance of seeing Jupiter but only in a bright sky before the stars became visible!

Finally the Jupiter’s Satellites program was RUN and the date entered for PLOTting at two-hourly intervals. A COPY was made of this screen display, too. There followed a frantic dash to the bottom of the garden where the telescope was permanently mounted. Luck was on my side! There, nestling in a gap in the rooftops was the planet Jupiter with four attendant moons in a ragged line — all clearly visible through the telescope. Reference to the printout for the Jovian satellites identified them as Europa, Io, Callisto, Jupiter itself and then, on the other side of the planet, a solitary Ganymede. All were in precisely the locations as predicted for that date and hour.

Some 20 minutes later at 18.20 GMT, Jupiter set behind chimney pots, but not before some of the Gavin family were roped in for a spy through the telescope. This shows that, even under pressure, the programs can be quickly chained together to find out the relevant information which makes astronomy more enjoyable. I hope that they add to your enjoyment.



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