The other day, while on a flight lesson, I gave my ETA to the ATC as 1145 zulu. My student asked me what is zulu time and why is it called that? I had to raise my left hand in a signal to ask him to listen to the radio conversation rather than interrupt with an intelligent question.
We landed at Sandown and climbed up the spiral stairs to meet the chaps in the tower so my new student pilot could see the relaxed, but professional and friendly the "service providers" are.
We did some searching on the web for ZULU time and its origins.... there are various explanations about where the term comes from; but the one that seems most likely to be the correct one to me is as follows.
The line we know as the Greenwich Meridian indicates the Sun is directly overhead this line at local noon. There are such lines or meridians in many cities like Paris, France and also in Oradea, Romania. In India, the ancient astronomers built large sundials from stone and metal to accurately predict solstices and eclipses.
In modern parlance, the Greenwich Meridian denotes the Zero time line, at Noon. On the east or west of this line, the time is different. Thus East of the Meridian, the time will be Z + 1 and on the west of the line, the time will be Z - 1.
The further east or west one goes, the time difference increases. The letter Z is phonetically pronounced Zulu.