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Ken Ward's Astrology Pages

Astrology: Calculating the MC.

clear.gif (807 bytes) The MC is the mid heaven when the birth occurred. On this page, we will use Mary as an example.

Mary was born  7 May 1982 at 11 hours 17 minutes AM, New Berlin, New York, USA. The longitude is 75 degrees, 20 minutes west of Greenwich. And the latitude is 42 degrees 37 minutes North of the equator.

We have already calculated Mary's sidereal time of birth, so all we have to do is to look in the tables of houses to find the ascendant. Mary's sidereal time of birth is:

1 hour 16 minutes 13 seconds.

The tables for the MC do not depend on the latitude, so we only need to look at the tables for the nearest MC to Mary's sidereal time of birth.

The American Ephemeris 1931 to 1980 contains tables of houses which we can use. There are, of course, many other sources.

You can look at the tables and pick the nearest MC. As the time is nearer 1 hour 16 than 1 hour 20, you can choose to look at the table for 1 hour 16. You can directly see that the nearest MC (shown at the top of each table) is 20ar24. The correct answer is 20ar37.

Accurate Computation of the MC

1 hour 16 mins 1 hour 20 mins
20ar34 21ar38

The difference between these two values for the MC is 64 arcminutes. We multiply this by the factor for time, previously calculated (0.05417). So the difference is:


3.47 or 3

The MC is therefore the lower value plus this correction: