will give some background to the original message sent from Arecibo, back in 1974. Arecibo is on the northern coast of Puerto Rico and contains a natural disc-shaped hole in the rock. Inside this bowl was constructed the world's largest radio-telescope, with a diameter of 1000 feet. In 1974 a number of modifications had been carried out to the transmitter, enabling it to broadcast signals at a power of up to 20 terawatts (1 terawatt = 1 trillion watts) and as an inaugural test of these improvements it was decided by SETI to transmit an encoded message to the heavens. This signal was aimed towards the globular star cluster M13, some 25,000 light years away and consisting of some 300,000 stars in the constellation of Hercules. The message was actually transmitted on November 16th 1974 and consisted of 1679 pulses of binary code (0's and 1's) - which took a little under three minutes to transmit. It was transmitted on a frequency of 2380MHz (which is significant later). Why 1679 digits? The reason for this is down to mathematics. 1679 is the unique product of two prime numbers; 23 and 73. Any sufficiently intelligent lifeform would no doubt look for unique, universal constructs - such as prime numbers, chemical element frequencies and binary digits. Don't forget that because we could be trying to communicate with an intelligence completely different to our own, we cannot talk in terms of 'human' systems, such as centimetres, feet, decimal numbers etc. Because ONLY the