Daylight Saving Time

Ham Radio operators need to be on the same time no mater their location. We use GMT time. This is Greenwich Mean Time, or Zulu time. This time never changes with the seasons . It is the same time in Perth, Australia as it is in Louisville, Ky USA. If I tell a Ham in Australia to call me at 09:00 December 22 GMT, both will be on the same day and time. I have a clock that displays the sun's travail across the world. I find this display very helpful in finding propagation of radio waves. At a glance, I can see where the sun is and where the terminator is located. (daylight - dark) (twilight)

Time is 9:35am March 11, 2019 local

The main purpose of Daylight Saving Time (called "Summer Time" in many places in the world) is to make better use of daylight. We change our clocks during the summer months to move an hour of daylight from the morning to the evening. Countries have different change dates.
The idea of daylight saving was first conceived by Benjamin Franklin.
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Daylight Saving Time

The Pros and Cons of Daylight Saving Time
Ever since the very first time Daylight Saving Time (DST) was introduced about 100 years ago, people have disagreed about whether setting the clocks one hour forward in the spring and back again in the fall has the desired effect.

http://www.timeanddate.com/time/dst/daylight-saving-debate.html