Ken Ward's Astrology Pages

Astrology: Calculating Local Sidereal Time for an Eastern Birth.

We will continue using the midnight ephemeris, but in this case, we will use a birth that occurred to the East of Greenwich.

Charles Aznavour was born in Paris on May 22, 1924 at 0:15 am. The longitude is: 002E20, and the time zone is 1

We need to calculate the local mean time and the local sidereal time to look up the house cusps in the table of houses.

Local Birth Time

Charles was not born on the Time Zone meridean, so some corrections are needed to find his local birth time. Time Zone 1 is 15 degrees, so he was born to the West of the Time Zone. He was therefore born earlier than the civil time of his birth.

The difference between his birth place and his time zone (15º) is:

15 deg - 2 deg -20 arcminutes =12 deg 40 arcminutes

15 degrees of longitude represent one hour in time, so this difference is:

(12 deg 40 arcminutes)/15 hours=

12.66667/15 hours=

0.84444 hours =

50 minutes 40 seconds

Because he was born to the East of the time zone, the local time was earlier than the clock time. We need to subtract this difference from the clock time of birth.

His local time of birth is therefore:

0 hours 15 minutes -50 minutes -40 seconds

We need to add 24 hours to the civil birth time so we can subtract:

24 hours 15 minutes

And subtract the correction for longitude difference:

-50 minutes -40 seconds=

Giving us the local mean time of birth:

23 hours 24 minutes 20 seconds

The previous day, so his corrected birth date is May 21st, 1924, at 23 hours 24 minutes 20 seconds.

Because we go back in day, we will use the sidereal time from the ephemeris for the previous day to that of birth.

Local Sidereal Time

We use this to look up the ascendant, MC, and house cusps.

Using the midnight ephemeris, we simply add the local time of Charles' birth to the sidereal time in the ephemeris for his day of birth. We always add this, whether the birth was in the East or the West. This will be for 21 May 1924, the previous day:

15 hours 53 minutes 26 seconds (Sidereal Time from ephemeris, previous day) +

23 hours 24 minutes 20 seconds (Local mean time of birth, calculated above)

This comes to 39 hour 17 minutes and 46 seconds.

We subtract 24 hours to bring this time within the nornal range:

15 hour 17 minutes 46 seconds

This is the uncorrected local sidereal time of birth. We need to apply some corrections.

Acceleration

Because sidereal time is faster than regular time, we need to correct this figure (the local sidereal time) by allowing 10 seconds for every hour, or part thereof. A sidereal day is approximately 3 minutes 56 seconds short of a regular day, so we need to accelerate regular time to accord with sidereal time.

Because we added

23 hours 24 minutes 20 seconds

At 10 seconds per hour, the correction is 23x10+24/60*10+20/3600*10 seconds, which is 234 seconds (approx), or 3 minutes 54 seconds, but also deduct 4 seconds special correction. We add this to our sidereal time so far:

15 hour 17 minutes 46 seconds (uncorrected local sidereal time, from above) +

3 minutes 56 seconds -4 seconds =

15 hours 21 minutes 38 seconds

Time Zone Correction

We need a further correction for each 15 degree time zone. This is 10 seconds per zone (15º). One time zones make 10 seconds.

Charles was born 12 deg 40 to the East of the time zone (15 degrees), so the correction we need, noting that 12º 40' is 12+40/60, or 12.67 approx, as a decimal. So the correction is:

12.67/15x10 seconds=

8 seconds (approx)

Subtracting this correction (because the birth is to the East) we get the sidereal time for his place of birth as:

15 hours 21 minutes 38 seconds (calculated above) -

8 seconds (time zone correction, calculated above)=

15 hours 21 minutes 30 seconds (which is the local sidereal time of birth)

We use the local sidereal time of birth, 15 hours 21 minutes 26 seconds, to look up the houses in the table of houses.