GMT, Greenwich Mean Time, used to be adopted by England and it is now substituted by UTC beginning 1967. GMT is only used as time zones now.
UTC, Coordinated Universal Time, is the time we used across the world starting from 1967. It is not the time zone. It has more than 12 “time zones”.
England is at GMT-0. New York is in GMT-5. China is GMT+8. The time between New York and China is 13 hours.
360 / 24 = 15 degree per hour.
Every year, some countries move their clock 1 hour faster and move it back in the autumn. The idea is to “make” more sunlight in the summer by having the sun to rise and set later, which give people more time after work. Or better yet, it conserves more energy since people don’t stay indoors. This is called the Daylight Saving Time. While the rest of the year is called the Standard Time.
In the USA, Hawaii and Arizona doesn’t follow DST because of their geographic reasons. It is a controversial topic on whether the DST would still save money at today’s society.
Benc Tan 