Greenwich mean time (GMT) or universal time (UT) is the mean solar time on the Greenwich meridian reckoned in days of 24 mean solar hours written as 00^h at midnight and 12^h at noon. To convert the above times to those of the other standard time meridians, add 1 hour for each 15^o of east longitude of the desired meridian and subtract 1 hour for each 15^o of west longitude. This table was compiled from data supplied by the Nautical Almanac Office, United States Naval Observatory.