It wasn't intended, honestly.
You see, I'd been playing with astable multivibrator circuits (AKA flip-flops), and had built a couple of quite small ones, with red and green LEDs to show which side of the circuit was active.
Then, it occurred to me, that I could put these circuits inside balloons...
So I put them inside a couple of three foot, white balloons, and then filled the balloons with hydrogen.
(Made the hydrogen by dissolving aluminium foil in a strong solution of caustic soda).
Then, because I had two giant balloons, which were each alternately flashing red and green... I tied the two balloons together with a short length of string, and released them into the night sky.
Next thing I know, people are phoning radio stations in Canberra (where I was) and reporting a UFO performing impossible manouvres in the sky.
I am ashamed that I caused this, I was just playing with stuff for my own entertainment.