Without timezones, you need a lookup table for what daylight hours are for every location on earth. For convenience, rather than publishing a table for every la

Without timezones, you need a lookup table for what daylight hours are for every location on earth. For convenience, rather than publishing a table for every latitude/longitude, let's group these locations along geographical borders nearby to longitude lines. We can call these grouping "zones", or in more broad contexts, "time zones." Hang on a second...