why does each time zone extend 7 1/2 degrees oneach side of central meridian rather than extending from 0 degrees to 15 degree?
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i have no idea ..
Each time zone extends approximately 7 1/2 degrees on each side of the central meridian to account for the natural rotation of the Earth and to facilitate global timekeeping.
To understand why time zones are divided in this way, let's start with the concept of timekeeping. The Earth rotates once every 24 hours, which causes the cycle of day and night. To maintain consistent timekeeping across different regions, it was necessary to establish a system that divides the Earth into standardized segments called time zones.
The Earth is divided into 360 degrees of longitude—the imaginary lines that run from the North Pole to the South Pole. The main reference line for timekeeping is the Prime Meridian, which passes through Greenwich, London, and is assigned a longitude of 0 degrees.
To create time zones, it was decided to divide the Earth into 24 segments, with each segment representing one hour of time. The idea was to establish a standard time for each time zone based on the local solar time at the central meridian of that zone.
Since there are 360 degrees of longitude and 24 time zones, each time zone covers approximately 15 degrees of longitude. However, for practical and administrative reasons, it was determined that each time zone should extend roughly 7 1/2 degrees on each side of the central meridian. This ensures that the majority of a country or region lies within a single time zone, making timekeeping and scheduling easier.
By dividing time zones in this way, countries and regions within a time zone can maintain relatively consistent time without having to deal with the frequent transitions that would occur if each time zone strictly covered exactly 15 degrees of longitude.