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Ken Ward's Astrology Pages
Astrology: Times for calculating houses and planets - idiot's guide Part 1
|This page deals with calculating GMT, which is used for
calculating the position of the planets. The next page
deals with calculating Greenwich Sidereal Time of birth, which is used for calculating the
house cusps, ascendent and MC.
On this page:
The time you need is Greenwich Mean Time (GMT). For practical purposes this is the same as:
The formula is simply:
The rule is: Add for West and subtract for East.
If this time is within the range 0 to 24 hours, then this is the time you use to look up (calculate) the position of the planets in an ephemeris. If the time is less than 0 or greater than 24, you need to use a date before or after the birth date.
If you use the Time Zone as stated, then it isn't necessary to bother with daylight saving time, etc. For example, Atlantic Standard Time is +4 hours. Atlantic Daylight Time is +3 (or +4-1 daylight saving). India Standard Time is -5:30. India Daylight Time is -6:30 (or -5:30-1 daylight saving).
If you use the current time zone, which takes into account daylight saving, etc, then the formula is simply:
The current time zone is used below.
If the above sum is less than 24 hours (negative), you use the previous day from birth. That is, if you need to add 24 hours to bring the time into the range zero to 24, then use the previous day in the ephemeris.
If the above sum is greater than 24 hours, and you need to subtract 24 hours, then you use the next day in the ephemeris.
Otherwise, of course, you use the birth date.
Ann was born in Idaho City (43N50, 115W50), USA on 18 July 1963 at 2:18 p.m. The Standard Timezone is UT-8 (120º W) and Summer Time was in operation (PDT=UT-7). Greenwich Mean Time (GMT) is simply:
The date to look up in the ephemeris is the birth date, 18 July 1963.
Alternatively, we can use the daylight saving information and the standard time zone:
Brian was born in Los Angeles (34N03, 118W15), USA on 3 February 1985, at 8:42pm. There was no summer time and the Standard Time Zone is PST (-8 hours, 120º). The GMT time of birth is:
We therefore look up the planets in the ephemeris for the next day, 4 February 1985, using the time 4:42am.
Ivan was born in Leningrad (59N55, 30E15) on 1 July 1959, at 11:15am. The time zone is UT+3, we deduct the 3 hours from the birth time to get UT:
Ruth was born in Jerusalem, Israel (31N46, 35E14) on 16 May 1959, at 1:05am. The timezone is EET, which is UT+2 hours. The UT time of birth is therefore:
We therefore look up the planets in the ephemeris for 15 May 1959 at 23:05 p.m.
We can find the planets' positions in the ephemeris by calculating the position from the UT of birth, using the appropriate date, either the birthday, or the day before (eastern) or the day after (western), if necessary. There is no difference between a Northern birth and a Southern birth in this respect. Therefore, what has been said above for Northern births is directly applicable to Sourthern births.
Kiri was born in Gisbourne New Zealand, on 6 March 1944, at 2pm. The timezone is UT-12. Therefore the UT of birth is:
We look up the planets for 2am on 6 March 1944.
Francis was born in Montevideo, Uraguay (34S53, 55W11), on 13 January 1972, at 6:30 am. The TZ is UT-3, so the UT of birth is:
We therefore look up the planets in the ephemeris on 13 January 1972 at 9:30 am.