I decided to make this tutorial because the art of manually calculating a natal chart is getting lost. It’s very important for beginning astrologers to master at least the calculation of the natal chart by hand. It gives important insight into the movement of signs and planets and will later help develop a better understanding of transitions and progressions. You will have missed something if you use online calculators like Astrodienst or astrology programs.

What you will need for this tutorial is the following:

• Time zone and daylight savings information (timeanddate.com).
• Ephemeris (see Astrodienst)
• House tables (Placidus)
• Logarithm tables in 24 hour format (as a free service from AFAD)

The only thing I won’t be able to help with is the house tables, since I didn’t find them online. It is recommended to buy an Ephemeris with Placidus house tables for all latitudes, since you will need to reference it often in predictive astrology.

The order in which a natal chart is calculated is as follows:

1. Determining latitude and longitude of the place of birth.
2. Determining GMT + Local Time.
3. Determining Star Time with the Local Time and Longitude of birth.
4. Looking up the house positions using the Star Time and Latitude.
5. Determining Planetary positions with the GMT and log tables.
6. Drawing up the chart.

Below the cut, all is explained. I will be taking my own birth information as an example. The details are: Heerlen (the Netherlands), 31st of August 1981, 17:50 hours.

Are you ready to begin?

1. Determining latitude and longitude of the place of birth.

There is an easy and a hard way of doing this. The easy way is going to google maps and look up an address. After that you need to paste into the browser location bar:

javascript:void(prompt('',gApplication.getMap().getCenter()));

This will give you: (50.88304, 5.980935) for my place of birth. The old fashion way is by taking out an Atlas and measuring the difference between the two nearest latitude or longitude lines. Now you know how many centimeters or inches one latitude or longitude square is. If you then continue to measure the distance until the birth place you will only need to divide it.

Example:
50.30 to 51 degrees latitude = 6cm equals 0.30 (half a degree)
You found your birth place at 1/3rd of that distance measured from the left = 0.10.
Now you know your birth latitude = 50.40.

2. Determining GMT + Local Time.

The Netherlands is usually 1 hour from GMT, but I was born in summer and the Netherlands has daylight savings in place. This means I should subtract two hours from my birth time to find the GMT.

17:50 CEDT (Central European Daylight Time)
02:00- (Timezone difference to GMT + Daylight Savings)
—–
15:50 GMT

To get greenwhich mean time it is important to remember that East of the line you need to subtract the hours and West you will need to add the hours.

The local time is actually the time when the Sun is exactly over your birth place. “Zone time” is not precise enough in astrology, since there is quite some difference between one zone and the other. This is why Local Time needs to be calculated. We can calculate the Local Time by adding 4 minutes for every degree of longitude. As established in 1. the longitude of my birth place is around 6 degrees East.

15:50 GMT
00:24+
—–
16:14 LT

For every degree of longitude East, we add 4 minutes to the GMT. For every degree of longitude West, we subtract 4 minutes from the GMT.

3. Determining Star Time with birth time and longitude.

Take out your Ephemeris and look up the star time for 31st of August 1981. It is usually the first column. Write it down. There are three corrections that need to be done to this time. The first one is:

For every 15 degrees of longitude subtract 10″ (10 seconds) for East, add for West.

22.36’20″
00.00’03″-
——-
22.36’17″

The second correction is adding the Local Time. This is always added, regardless if East or West.

22.36’17″
16.14’00″ +
——-
38.50’17″

The third correction is adding 10″ (10 seconds) for every hour of Local Time, regardless if East or West.

38.50’17″
00.02’43″ +
——-
38.53’00″

As a last step we need to subtract 24 hours from the star time since the day doesn’t have 38 hours. Remember that 1 degree = 1 hour.

38.53’00″
24.00’00″
——-
14.53’00″

The corrected star time is: 14.53’00″.

4. Looking up the house positions with Star Time and latitude.

House tables are ordered by Latitude. This means we’ll need the Latitude of the birth place. In my case that is 51 degrees North. At the corresponding Latitude in the house tables you will need to look up the corrected star time (usually in the first column). The nearest value will give you the house locations.

15 SC 28 for MC
5 SA 23 for 11
22 SA 21 for 12
10 CP 25 for ASC
1 PI 55 for 2
17 AR 8 for 3

5. Determining planetary positions with the GMT and log tables.

The planetary positions mentioned in the Ephemeris for your day of birth are written down for 00:00 hours GMT. There are some Ephemerises that do it for 12:00 hours GMT, so please be careful with the difference. For this tutorial I’m assuming you have an Ephemeris for 00:00 hours GMT.

Since you now know they are written down for GMT, you we will need to calculate the distance travelled until the GMT of your birth. My GMT was 15:50 hours. The conclusion is that the planetary positions would have moved more than half between the values of 31st of august and september 1st. To calculate this exactly, we need to find out the Daily Distance Travelled (DDT). A planet has a different DDT for a given day, though in general their distance travelled in a day is around 1 degree for the Sun, 12-14 degrees for the Moon, etc.

Calculating DDT ex. the Sun
8.28 VI – 1st of September.
7.30 VI – 31st of August.
——
0.58

We’ve established here that the DDT for our example, the Sun, is 0.58′ (58 minutes). All we have to do now is use the log tables as a way of finding the number of minutes travelled until 15:50 GMT. First, look up the logarithmic value for 15:50, this is .1860.

1.3949 (log for 0.58′)
0.1860 (log for 15:50′) +
——
1.5809

All you have to do is look back 1.5809 in the log tables, which equals 38 minutes. Now add 38 minutes to 07.30 VI, the location of the Sun at 00:00 GMT.

07.30
00.38 +
—–
08.08 VI

There you have it, for my natal chart the Sun is located 08.08 in Virgo.

Tricky planets and their DDT

The moon might pose some more difficulty since she is often times overriding a sign in the daily distance travelled. A sign is 30 degrees so if you go over that value, it means the planet position is in the next sign.

Retrograde planets are a special case as well. The name says it: these are planets seemingly going backwards from the viewpoint of the Earth. The daily distance is calculated by reversing the days. So you won’t be subtracting the value of 31st of august from 1 september, but the other way around. Whatever value you added under normal circumstances needs to subtracted for Retrograde planets.

Sometimes there’s no difference between the position of a planet on your birthday and the next day. This means the planet is Stationary, often indicated by S. or St. in calculated charts. It means that from Earth the planet appears to be standing still.

Both retrograde and stationary are the results of Geocentric astrology, as most Western astrology is.

6. Drawing up the chart

It of course helps if you have empty horoscope forms, but if you don’t drawing a circle and dividing it into 12 pieces will do fine as well. What you always must remember is the following:

Signs on the house cusps move clockwise, planets move counter clockwise. Here is a beginners error:

Left: Correct placement of Pluto.
Right: Incorrect placement of Pluto.

Conclusion

With this tutorial you should now have an understanding of how the charts calculated by software or Astrodienst come together. I failed a lot of math tests, but I’ve been calculating natal charts like this since I was 13 years old. Perhaps one made me fuck up the other. lol. Perhaps I should have layed off trying to do fractions with degrees.