To begin with, we need to convert the time of birth into Greenwich Mean Time (GMT), and then from GMT into Sidereal Time, which is the true or real time derived from the orbits of the planets.
Note down the time of birth, and then the latitude and longitude of the place of birth - these co-ordinates can be found in an atlas, or on the internet at heavens-above.com, an online resource offering useful astronomical data. The birth time should be entered as am or pm from the 12-hour clock system rather than using the 24-hour clock and then convert it into Greenwich Mean Time if the birth was outside the UK. For example, if the subject was born in Toronto, Canada five or six hours must be subtracted (depending on current UK Summer Time) because the sun rises five hours later than it does in Greenwich, London. If the birth occurred during Summer Time in the UK, the relevant hour is deducted to arrive at the actual time of birth at GMT.
The next stage is to find the Sidereal Time at noon from the relevant ephemeris which is written in after the GMT time of birth. The amount of time before noon or past noon then has to be worked out. For instance, someone born at 1am GMT has an interval of eleven hours before noon, whereas someone born at 5.30pm has an interval of five hours and 30 minutes after noon. The interval is added (pm births) or subtracted (am births) to the Sidereal Time at noon to form a new Sidereal Time.
One more slight adjustment is required - the - acceleration on the interval". This is because Sidereal Time is actually four minutes per day faster than GMT. Ten seconds should be added (pm birth) or subtracted (am birth) for every hour of difference. Someone born at 1am (eleven hours to noon) will require a deduction of 110 seconds, that is one minute 50 seconds, whereas a birth occurring at 5.30pm (five hours and 30 minutes from noon) requires an addition of 55 seconds. This minor adjustment gives the correct Sidereal Time at Greenwich at birth.
The final process is to find the Local Sidereal Time for all births outside the 0-degree Greenwich longitude. This is called the longitude equivalent and requires the multiplication of the longitude figure by 4.
For example:
Longitude for Leeds, UK, is 1 degree 32 minutes west x 4 = 6 minutes (M) to be deducted from Sidereal Time.
Longitude for Adelaide, Australia is 138 degrees 36 minutes east x 4 = 9 hours (H), 15 minutes to be added to Sidereal Time.
Proceed to Step 2 >>
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