Military time, which uses the 24-hour time standard, begins each day at midnight, which is called 0000 hours. 1 AM is referred to as 0100. Noontime is 1200 hours, 1 PM is 1300, 2 PM is 1400, etc.

Coordinated Universal Time follows a similar format, but the start time of each day depends on a person's location on the globe. UTC, typically referred to as Greenwich Mean Time, or ZULU time, has as its origin Greenwich, England. When it is midnight in Greenwich, we consider that to be the beginning of a new day worldwide. Why one time standard? Imagine communicating with an amateur radio operator on the other side of the Earth. Most hams maintain a log book which includes information about frequency used, time, and remarks. Matters are greatly simplified when all operators include a time entry which is the same worldwide. Rather than noting local time, entries are typically written as UTC. For similar reasons, NASA maintains all of its times in UTC, and all satellite tracking software requires the knowledge and use of UTC.

Convert local time to UTC time

  1. Use the charts to determine the local and UTC times. Minutes are read as they normally are. For example, if a satellite is due to pass over our location from 8:23-8:37 AM local, this would correspond to 1223-1237 UTC.
  2. Ask your students to convert their current bell schedule using UTC time. What time do we:
  • Go out to recess?
  • Return from recess?
  • Go to lunch?
  • Get dismissed from school?
  • Go to sleep?

If you're going to be tracking satellites on a regular basis or over an extended period, you may want to locate a second clock, set to UTC, or ZULU time, in your classroom.


  • Accurate digital watch (UTC time is broadcast 24 hours a day on the following shortwave frequencies: 5000 Mhz, 10.00 Mhz, 15.00 Mhz)