Astro-Databank:Handbook chapter 18

From Astro-Databank
Jump to: navigation, search

Handbook navigation:
Overview | ch.1 | ch.2 | ch.3 | ch.4 | ch.5 | ch.6 | ch.7.1 | ch.7.2 | ch.8 | ch.9 | ch.10 | ch.11 | ch.12 | ch.13 | ch.14 | ch.15 | ch.16 | ch.17 | ch.18

18. Local Mean Time of Sunrise for Latitudes

The method of calculating Location Time (or City Time) as well as calculating LMT or any local time to the reference location by which the birth was timed:

1. Time meridians are designated for every 15 degrees of longitude, which equates to one hour of time. There are 24 one-hour meridians around the earth:

 24 x 15 = 360 degrees of longitude, or    24 hours of time
            15	degrees of longitude equals  1 hour of time
             1	degree of longitude equals   4 minutes of time
             1	minute of longitude equals   4 seconds of time
                                        Greenwich
                      +                     |                    -
                     West                   |                   East
    If birth is West of Greenwich, add      |   If birth is East of Greenwich, subtract
    the correction to find what time it is  |   the correction to find what time it is
              at Greenwich (GMT)            |            at Greenwich (GMT)

Example: Person born at 9:00 a.m. in California at PST meridian (8 hr. west) = +8 hrs:

   9:00 a.m. plus 8 hrs = 17:00 GMT.

Example: Person born at 9:00 a.m. in Europe at MET (or CET) meridian (1 hr east) = -1 hr:

   9:00 a.m. minus 1 hr = 8:00 GMT.

2. When the birth is recorded on LMT (local mean time), the correction of longitude to time is made in reference to the meridian location.

                                        Location
                    -                       |                  +
                   West                     |                 East
 If birth is West of the location, subtract |   If birth is East of the location, add
   the correction to find what time it is   |   the correction to find what time it is
            at the location (LMT)           |            at the location (LMT)
       Example: Person born 9:00 AM LMT,          Example: Person born 9:00 AM LMT,
        in San Francisco (122 W.25)                   in Los Angeles (118 W.15)
         PST meridian is 120 W.00                     PST meridian is 120 W.00
                 122 W.25                                   120 W.00
                 120 W.00                                   118 W.15
                 --------                                   --------
                   2   25                                     1   45
                  x4   x4                                    x4   x4
                 --------                                   --------
                   8' 100" =0"                                4' 180" = 7'00"
                9:00AM  LMT                                 9:00AM  LMT
                  -9'40"  =                                   +7'00"  =
                -----------                                 -----------
                8:50:20 LMT                                 9:07:00 LMT
      (which is then 8 hrs plus to GMT)          (which is then 8 hrs plus to GMT)

3. Rather than correct the LMT to the nearest meridian, the correction may be made directly to Greenwich to find GMT.

          San Francisco, CA                            Los Angeles, CA
              122 W.25                                   118 W.15
               x4   x4                                    x4   x4
              --------                                   --------
              488' 100" =                                472'  60" =
              489'  40" =                                473'  00" =
              8 hrs 9 min 40 sec plus to Greenwich =     7 hrs 53 min plus to Greenwich =
              17:09:40 GMT                               16:53:00 GMT

4. When a birth is recorded on a location time, such as Paris time, Rome time, etc, the correction of the birth time is made to the reference point of the location.

 Example: Person born at 9:00 AM Paris time        Example: Person born at 9:00 AM Paris time
          at Marseilles, France, 5 E.24.                    at Ault, France, 1 E.27.
          Marseilles 5 E.24                               Paris 2 E.20
               Paris 2 E.20                               Ault  1 E.27
                     ------                                     ------
                     3'   4"                                    0'  53"
                    x4   x4                                    x4   x4
                    -------                                    -------
                    12'  16"                                    0' 212" = 3'32"
 Marseilles if east of Paris so the correction     Ault is west of Paris so the correction
 is added to find the time at Paris =              is subtracted to find the time at Paris =
                     9:00 AM Paris time                         9:00 AM Paris time
                      +12:16                                      -3:32
                     -------                                    -------
                     9:12:16 AM LMT                             8:56:28 AM LMT

5. Birth recorded to a location time such as Paris time, Rome time, etc, may be corrected directly to GMT by using the standard correction of the reference location.

  Example: Person born at 9:00 AM Paris time   |   Example: Person born at 9:00 AM Paris time
           at Marseilles, France, 5 E.24.      |            at Ault, France, 1 E.27.
                                               |
                             0 West        Greenwich        0 East
                                          Paris 2 E.20
                                               x4   x4
                                               --   --
                                                8'  80"
                                              = 9'  20"

Paris is 2 degrees 20 minutes east of Greenwich; multiple degrees and minutes of longitude by four to find minutes and seconds of time. The Paris time correction will always be minus 9'20", to Greenwich.

In both examples, the birth time of 9:00 AM Paris time may be corrected to Greenwich by subtracting 9'20" = 8:50:40 AM GMT. In common practice, the seconds are often rounded off to the closest minute.


Personal tools