Why does each time zone extend 7 1/2 degrees on each side of central meridian rather than extending from 0 degrees to 15 degree?
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Each time zone extends 7 1/2 degrees on each side of the central meridian because this allows for the most accurate representation of local time within a particular region. The Earth is divided into 360 degrees of longitude, and there are 24 time zones in total (one for each hour of the day). Therefore, each time zone covers approximately 15 degrees of longitude.
However, it is not practical to simply divide the Earth into 24 equal time zones of 15 degrees each. This is because the Earth is not a perfect sphere, but rather an oblate spheroid with variations in the size and shape of its landmasses.
To accommodate these variations, the International Meridian Conference held in 1884 determined that time zones should be defined by lines of longitude that are multiples of 7 1/2 degrees away from the central meridian. The central meridian is typically taken as the Prime Meridian, which passes through Greenwich, London.
By extending each time zone 7 1/2 degrees on each side of the central meridian, the time zones align more closely with political and geographical boundaries. This helps to simplify timekeeping and ensure that neighboring regions have relatively synchronized time.
If you would like more specific details, I recommend visiting the provided link for a more comprehensive explanation and additional resources on time zones and latitude.