Ascendant and Midheaven Manual Calculation
The first step in calculating a birth chart is the calculation of two important points:
- The Ascendant (the sign rising on the eastern horizon at the moment of birth)
- The MidHeaven ( where the ecliptic crosses the subjects line of longitude)
There is a slightly different set of calculations depending on whether the subject is born in the northern or southern hemisphere.
In order to calculate these 2 points we need to find:
Local Sidereal Birth Time
Sidereal Time at Place of Birth
Worked Example
Step 1: Find data for Date, Place and Time of Birth
- Birth Date: 23rd Nov 1944
- Birth Place: New York
- Birth Time: 4 am
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Step 2: Find Latitude and Longitude of Place of Birth
From the section of the atlas in the image below we have:
- Latitude: 40°, 45’ N
- Longitude: 74° 00’ W
Step 3: Convert this local time of birth to GMT at their time of Birth
This can be found in 2 ways:
- Look up in an atlas containing standard time zones:
The image above shows a 5 hour difference and November is outside of daylight saving time so no further adjustment needed. 4am Eastern Standard time is 4+ 5 Hours GMT = 9am. So at their time of birth at 4am, it was 9am GMT.
- The second way of calculating this interval is mathematically as following
Solar Day = 24 hours and earth rotates 360°
Therefore in 1 hour earth rotates = 15°
- From step 1 we found : Longitude: 74° 00’ W
Since 15° = 1 hour
74° = (1/15) x 74 = 4.93 hours which we approximate to 5 hours.
GMT at their time of Birth = 9am
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Step 4: Calculate the equivalent Sidereal Time at Greenwich
In the previous step we converted local time of the subject to GMT and we now have to do another conversion. Sidereal time relates to the exact time the earth takes to revolve around its axis compared to the Solar Time which is an approximated 24 hours that we use for convenience day to day.
- Find Sidereal Time for Noon at Greenwich:
To find this we need to look at the relevant atlas tables:
Sidereal Time at noon Greenwich on Nov 23rd 1944 = 16h, 9 min and 20 secs
- Find the Interval (Difference) between GMT and Noon Sidereal Time for their dates of birth
- Subjects GMT of Birth = 9am (from step 3)
- Count forward to noon GMT = 12 am (9am + 3 hours)
- Subjects noon Sidereal Time of Birth = 16H, 9 min and 20 secs (from step 4)
- Subtract 3 hours from 16 hours 9 min and 20 secs
Answer: 13 hours, 9 min and 20 secs
- Find Acceleration on the Interval Calculated Above
Acceleration on the interval is another adjustment that needs to be done to allow for the difference between sidereal and solar time.
Acceleration Adjustment:
For every hour of interval time (+ or -) 10 secs
For every 6 minutes (+ or -) 1 sec
(Am = subtract, Pm = add)
[Interval = 16H, 9’ 20 secs – 13H, 9’ 20 secs
= 3 Hours]
Using Acceleration Adjustment 3 x 10 secs = 30 secs
As the birth time is 4 am then we subtract:
13H, 9’, 20 secs – 30 secs = 13H, 8’, 50 secs
Sidereal Time at Greenwich for TIME of Birth = 13H, 8’, 50 secs
Step 6: Find Sidereal Time for Place of Birth at Time of Birth
This difference is the difference in time between place of Birth and Greenwich It is called the ‘Longitude Equivalent in Time’
Longitude of N.Y. = 74º
360/24 15 degrees in 1 hour.
Every minute therefore we have 60/15 = 4º rotation of the earth.
N.Y. is 74º longitude from Greenwich which means 74 x 4º = 296 minutes
296 minutes/ 60 = 4.93 hours = 4 hours and [93/100] x60 = 56 mins
Sidereal Time at Greenwich for TIME of Birth = 13H, 8’, 50 secs.
N.Y. is WEST of Greenwich and so we subtract to find the equivalent time in N.Y
13 Hours 8 mins 50 secs – 4 Hours 56 mins
= 8 Hours 12 Mins 50 secs
Local Sidereal Time at Birth = 8 Hours 12 Mins 50 secs
Step 7: Finding the Ascendant and Midheaven from the Atlas
Below is a table showing the Ascendant and MidHeaven for the year 1944 at different latitudes:
Across the top are the latitudes and we stop when we find the one (highlighted in yellow) which is the closest to the subject.
Along the Y-axis we stop at the Sidereal Time which is closest to that of the subject. We calculated a sidereal time of 8 hours, 12 mins and 50 secs above. The closest match in the table is highlighted in yellow at 8 Hours, 12 minutes and 54 secs.
Sidereal Time Used = 8H 12 Minutes and 50 secs
- Y. Latitude = Latitude: 40°, 45’ N
From the above table we can conclude that the subject has
Ascendant 1º Leo
Midheaven of 26º and 17’ Libra