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Local Mean Time The UTC of any event observed from the Greenwich meridian. All times (sunrise, twilights, meridian passage, etc) listed in the Nautical Almanac are given in terms of LMT— that is, they tell you what time this will happen in UTC for observers at Greenwich. To figure the actual UTC you should observe for these events from a western DR-Lon, convert your DR-Lon to time using the Arc to Time table in the Nautical Almanac and then add this time interval to the listed LMT of the event. In east longitudes, subtract this interval from the tabulated LMT. Once you have figured the UTC of the event this way, you can figure watch time, by reversing whatever you normally do to your watch time to figure UTC from it. See Greenwich mean time and Watch Time. __________________ For a bit of celestial navigation humor, here is the official definition of LMT from Bowditch. Local Mean Time "The arc of the celestial equator, or the angle at the celestial pole, between the lower branch of the local celestial meridian and the hour circle of the mean sun, measured westward from the lower branch of the local celestial meridian through 24 hours; local hour angle of the mean sun, expressed in time units, plus 12 hours. Local mean time at the Greenwich meridian is called Greenwich mean time, or Universal Time." Abbreviation:  LMT

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