> The solution is to just use UTC. That’s it. Okay. I work in Minneapolis and need to schedule a meeting with someone in London. How do I know what UTC time is

> The solution is to just use UTC. That’s it. Okay. I work in Minneapolis and need to schedule a meeting with someone in London. How do I know what UTC time is during daylight hours for both participants? Well, we can use a formula that will tell us where the sun in the sky for a given longitude. But that's kind of a chore. So let's break ranges of longitude into zones and create a lookup table. Hang on a minute... I've just traveled to Tokyo from Minneapolis. What time do I need to set my alarm to, to wake up an hour before most businesses open? Well, I can use trigonometry to figure out what UTC time the sun will rise at this location on Earth. But that's kind of a chore, so presumably each city will have an offset from UTC time that they all agree on to begin business hours. Hang on a minute...