英語 English：Time zone
日語 Japanese：タイムゾーン
類義 Synonym：World time Local time
意味 Meaning：A time zone is a set of times for each longitude in the east and west.
For example, the longitude of Tokyo (東京) is 139.7 degrees east, so the time zone for Tokyo is set at UTC+9 (Universal Time Coordinated plus nine hours). The longitude of Shanghai (上海) is 121.4 degrees east, so the time zone of Shanghai is set at UTC+8.
Therefore, the time difference between Tokyo and Shanghai is 9 - 8 = 1 hour.
教材 Learning materials：Time zones East Asia 2020 PDF Download
解説 Commentary：
Time zones are defined by longitude in the east and west, based on UTC (Universal Time Coordinated). UTC+0 is used in England.
The Earth's longitude ranges from 0 degrees east to 180 degrees east and from 0 degrees west to 180 degrees west. If you go around the earth once from east to west, you will travel 180 + 180 = 360 degrees.
Since the earth rotates once in 24 hours, one hour of time zone corresponds to 360 ÷ 24 = 15 degrees.