Why was Greenwich chosen to be the "time capital of the world"?

Question

Whose idea was it and why not somewhere else?

Answer 1

I'm not absolutely certain, so you may wish to do a web search under "time".  However, I believe Greenwich was chosen when England was the predominant sea power on earth and had an empire that spanned the globe.  Thus, it would make sense at that time to have Greenwich Observatory (near London) considered "home base" since London was the capitol of England, official home of Parliament and the sovereign,  and thus the center of power over both the most powerful navy on earth and the largest world empire.  Interesting question!

Answer 2

As the United Kingdom grew into an advanced maritime nation, British mariners kept at least one timepiece on GMT in order to calculate their longitude from the Greenwich meridian, which was by convention considered to have longitude zero degrees. This did not affect shipboard time itself, which was still solar time. This, combined with mariners from other nations drawing from Nevil Maskelyne's method of lunar distances based on observations at Greenwich, eventually led to GMT being used world-wide as a reference time independent of location. Most time zones were based upon this reference as a number of hours and half-hours "ahead of GMT" or "behind GMT".

Greenwich Mean Time was adopted across the island of Great Britain by the Railway Clearing House in 1847, and by almost all railway companies by the following year from which the term "railway time" is derived. It was gradually adopted for other purposes, but a legal case in 1858 held "local mean time" to be the official time. This changed in 1880, when GMT was legally adopted throughout the island of Great Britain. GMT was adopted on the Isle of Man in 1883, Jersey in 1898 and Guernsey in 1913. Ireland adopted Greenwich Mean Time in 1916, supplanting Dublin Mean Time.[1] Hourly time signals from Greenwich Observatory were first broadcast on 5 February 1924.