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Tables of Houses, Atlases,
Calculation Aids, page 2

Tables of Houses, etc., page 1

How to calculate houses using a table of houses

CHART PAD #12: 2 in 1 (biwheel) - Sophia Mason, $8.00
Inner & outer wheel to show natal & transits, or natal & progressions, or two natal charts (yours & a friend's). Two aspect grids & two element/quality boxes.

See this life size, in great detail (pdf).

AFA, oversize, 25 sheets.

CHART PAD #8 - AFA, $8.00
Single wheel, equally-spaced houses with degree markings on the outside edge. Use the degree markings with equal houses, or ignore them & use unequal houses (such as Placidus, Koch, etc.). Aspect grid includes space for declinations, box where you can total planets by element & quality.

See this life size, in great detail (pdf).

AFA, oversize pad of 50 sheets.

THE MATH OF ASTROLOGY, A step by step guide - Peter Murphy and Beth Rosato, $29.95


Preface to the revised edition

1. Getting ready
2. Preliminary birth time calculations
3. Preliminary sidereal time calculations
4. Calculating the house cusps
5. Calculating the planetary positions
6. Calculating the Part of Fortune and the Part of Spirit (aka Daimon - Dave)
7. Detecting and correcting errors
8. Copying data to the blank wheel
9. What do I do now?

Practice exercises

10. Calculating progressions: preliminary steps
11. Calculating the progressed planetary positions
12. Calculating the progressed midheaven and ascendant
13. Calculating the date & time of progressed contacts

Practical exercises

14. Interpreting progressed charts
15. Transits, returns, and other simple calculations

Worksheets for natal charts, progressed charts, and solar returns


Before I got my first computer program many years ago I had already calculated over 100 natal charts by hand and had found various short-cuts to the process. So I initially opened this book to natal chart calculations but was disappointed with what I read. So I next turned to the progressed section, to see if it might be different.

Regret that I am still disappointed. Page 86, the start of the instructions for progressed charts, table 14, Leap Years. There you will see the year 1900 given as a LEAP YEAR. It was, in the Julian calendar, which was in use in Russia at the time, but it WAS NOT in the Gregorian. Which has been in use, in England and America, since 1750, and in many other countries as far back as 1582. The change, from Julian to Gregorian, concerned century years not divisible by 400. Such as 1700, 1800 and 1900, NONE of which were leap years. The year 2000, evenly divisible by 400, was a leap year as we all remember. This book is the Revised Edition. Such an obvious mistake, in a book on calculation, should never have occurred.

So we have another fuzzy-headed book. I see a lot of books, I've come to think that "fuzzy" is all we can expect. On the back of the book it says,

The Math of Astrology is a simple, methodical, step-by-step guide for manual chart calculation with pencil and paper.
This is exactly true, but, regrettably, not of this book. Here is the simple method: My own.
  • You have the time of birth, am or pm
  • To the best of your knowledge, deduct an hour if it was daylight (summer time). If not, leave the time alone
  • You are in America, which is west of London. Subtract the proper number of hours (EST=5, PST=8, etc) to get GMT. For an early morning birth this may result in a GMT on the previous day. You will get used to this.
  • Go to your atlas. Look up the place of birth. There will be a number there. For New York, the number is 4:56. For Chicago, 5:50. For Los Angeles, 7:53.
  • ADD that number to your GMT
  • RESULT: The local mean time of birth (LMT). With this you can calculate planetary positions.
You want house cusps? This is rough'n'ready, not exact: Take your LMT. Go to your ephemeris for the day of birth. You will find the Sidereal Time listed there (ST). ADD the sidereal time to your Local Mean Time to get the Sidereal Time of birth. There are two minor adjustments to get that exact to the nearest second, but what you already have will be within four minutes of exact. If your birth time is approximate, you might as well stop here. Take the result, go to your Table of Houses, find the table with that Sidereal Time, then find the latitude of birth, and you have your house cusps.

In a nutshell, that's Dave's way of constructing a chart. You still have to figure out how to use your noon or midnight ephemerides and put up with adding & subtracting simple logarithms, but LMT and ST are the major steps.

In the Murphy/Rosato system, before you start you must know:

  • Base 60 !
  • Conversion of Base 60 to Base 10 !
  • The 24 hour clock !
  • All the world's time zone meridians !
  • If the place of birth is EAST or WEST of its meridian !
The East or West bit is important, because instead of a clean, simple conversion to GMT and then reduction to your LMT, as I showed you above, in the Murphy/Rosato system, for a New York chart, you must subtract 4:56 from 5:00 to get 0:04 (four minutes) and then figure out if you must ADD or SUBTRACT four minutes to your time of birth. The Eastern Standard Time Meridian, at 75 degrees west of Greenwich, happens to run darn near downtown Philadephia, but if you're in New York and a degree east of Philly (which is four minutes of clock time), do you ADD four minutes, or SUBTRACT four minutes? I've been in this biz a quarter century and off the top of my head, I STILL don't know. I have to look it up. Every time.

Well, if you guessed wrong and added instead of subtracted, you'll only be eight minutes wrong. When you're just starting out, a chart that accurate will be a godsend (trust me, I've been there), but if you were born in central Kansas, like me, the interval is 28 minutes. Get that wrong and you will be nearly an hour off, and there are many places on the globe where the clock on the wall is nearly a full hour from its proper (LMT) time (western Kansas), which makes for nearly two hour mistakes.

Which is why I invented my own system: Figure out if it's daylight or not, if it is, subtract an hour. Figure out how many hours it is back to Greenwich, which will always be the same for your time zone. Subtract that, then add the number in the atlas to your GMT (subtract if you're in Europe & therefore to the east of London), and, hey presto, you've got LMT. It's simple, it always works, you can't be fooled.

Murphy/Rosato's instructions for southern hemisphere house cusps are dreadful. Instead of having complete instructions at one place on a single page, with the reasons clearly stated, instructions are split between two pages, 14 and 21. For the southern hemisphere you are first told, in what amounts to a footnote, to add 12 hours to your Sidereal Time (pg. 14). Then, in what amounts to a second footnote on pg. 21, you are told to reverse the numbers of the resulting houses, where the MC becomes the IC, the ASC becomes the DSC, the second house becomes the eighth, etc. If you don't catch either of those footnotes, your South American charts will be somewhat wrong. If you only catch the first, your houses will be upside down. This is a common mistake. And, so far as reading a chart, it's a fatal one. For thirty bucks, we expect a book to help us avoid traps like this.

With progressed calculations, Murphy & Rosato are still murky. Page 88, they give instructions for the Adjusted Calculation Date (ACD), which makes looking up progressions in the ephemeris a snap. Only they don't call it that. They call it the "Midnight Date and Time". No one else does.

I've been in this biz a long time & if a casual glance finds errors and complications like these, how the heck can you, complete novice that you are, possibly understand what Murphy and Rosato are trying to teach you? You will flee back to your computer programs.

AFA, 172 pages, oversize.

Read the book? Want to tell the world? How many stars (1-5) would you give this book? Tell us!

For all you budding math junkies: Review of Plane Trigonometry, Elements of Spherical Trigonometry, the Celestial Sphere, Interpolation, etc. Appendices: Natural Trigonometric Functions to five places & Interpolation coefficients for Newton's Binomial Interpretation Formula. If you're bright & bored with computers, the purity of mathematics can be an unexpected delight. 62 pages. AFA, paper.

Contents: To proportion house cusps; To find the standard time; To orient a mundane chart; The computation of declination cycles; Computation of sunrise; To find the sidereal time; Basic trigonometric spherical diagram; To change right ascension to degrees, minutes and seconds; Detailed mechanics of changing right ascension and declination to (celestial) longitude and latitude; To compute the longitude of the sun; Computation of ingresses of sun and planets; Computation of conjunctions; To find the true node of the moon or a planet; Useful information of eclipses; To find the G.M.T. of the quarters of the moon. Appendix: Example math for sun time birth, solar return, progressions and increment table; Examples for near the international date line; "Once more around the wheel" directions (mundane). 74 pages including bibliography. AFA, paper.

BASICS OF ASTROLOGY, Vol. 3: Tables & Reference - Ove H. Sehested, $15.00

Contents: This is an appendix to (out of print) volumes 1 & 2.

Appendices: Acknowledgements, Feedback, Index to figures in the text; A. Raphael's ephemeris, sample page; B. Map of US time zones; C. Time zones of various countries; D. Systems of coordinates; E. AP [Aries Press] tables of houses, sample pages; F. Degrees or hours into decimals; G. How to use the electronic hand calculator;

H. Diurnal log tables; I. Latitude & longitude of various cities; J. Pluto ephemeris, 1900-1960; K. Correction factor table; L. Longitude into time; M. Declination of the Asc & MC; N. Synopses of calculations; O. Aspects; P. Sample chart form; Q. 360 chart form; R. Days of the year numbered; S. List of planet dignities; T. Decanates & their rulers; U. Table of mutual receptions;

V. Chart of the US (Gemini rising); W. "Ingrid's" chart; X. The Stockholm chart; Y. Encyclopedia of planets, signs & houses.

Comment: This book is mute testimony to the extent that computers, and Thomas Shanks, have changed astrology. Not so many years ago, a book like this would be indispensable.

AFA, 152 pages, numbered from 397 to 540 (includes 9 Roman numeral pages).

Tables of Houses, etc., page 1


Okay, you wanna know my secret method. Here it is:

The Requirements:

Midnight Ephemeris
Table of Houses (any will do)
An atlas of some sort (Shanks' are excellent)
For a birth NORTH of the Equator, and,
WEST of London, eg, somewhere in North America. Later you can adapt these rules for anywhere.

First: Convert clock time to GMT. Essentially, add

5 hours for EST
6 hours for CST
7 hours for MST
8 hours for PST

Example: Birth at 10:40 am, New York, November 14, 1965: Add 5 hours to get 3:40 pm GMT.

If it's a summer birth in the US/Canada, add

4 hours for EDT
5 hours for CDT
6 hours for MDT
7 hours for PDT

Example: Birth on June 14, 1976, 1:27 pm, Los Angeles. Add 7 hours to get 8:27 pm GMT.

If the GMT time is in the afternoon, convert to 24 hour time (eg, add 12). So 3:40 pm GMT is 15:40; 8:27 pm is 20:27.

Go to your atlas. Look up the city of birth. You will find the difference between local time & GMT listed for each city. Take this number and SUBTRACT it from GMT. This will give you LOCAL MEAN TIME (LMT). Our examples:

The New York Example: Birth at 15:40 GMT. New York time difference: 4:56. Subtract 4:56 from 15:40 to get 10:44 am LMT, New York.

The Los Angeles Example: Birth at 20:27 GMT. Los Angeles time difference: 7:53. Subtract 7:53 from 20:27 to get 12:34 pm LMT, Los Angeles.

(Notice this method automatically corrects for daylight time, but you still have to know if daylight was in use.)

Go to your ephemeris. Look up the sidereal time shown for the date of birth. If the GMT time is for the next day, look up that day, not the original day of birth. ADD this sidereal time to the LMT. Our examples:

The New York example: Ephemeris sidereal time for November 14, 1965: 3:32 (the ephemeris gives seconds, I've rounded). ADD this to the New York LMT of 10:44 am to get a Sidereal Time for your chart of 14:16.

The Los Angeles example: Ephemeris sidereal time for June 14, 1976: 17:30 (rounded). ADD this to the Los Angeles LMT of 12:34 to get 30:04. As this is greater than 24, subtract 24 to get a Sidereal Time for your chart of 6:04

The Fudge Factor: Go to your Table of Houses. Find the nearest Sidereal time for your chart. Then skip to the next greater Sidereal time. This is the fudge factor, a rounding up one notch in time. Look down the table to find the latitude of birth. Those are your house cusps. They will generally be accurate within one degree without any further calculation. Our examples:

The New York Example:
The sidereal time is 14:16. In the AFA Placidus Table of Houses, I found 14:16 on page 109. I skipped to the next table for 14:20. New York is 41 degrees north (from your atlas). The results:

MIDHEAVEN: 7 degrees, 21 minutes of Scorpio
11th house: 0 degrees, 53 minutes Sagittarius
12th house: 21 degrees 13 minutes Sagittarius

ASCENDANT: 12 degrees, 25 minutes of Capricorn
2nd house: 24 degrees, 50 minutes of Aquarius
3rd house: 6 degrees, 13 minutes of Aries.

The computer gives an ascendant of 12 degrees, 11 minutes Capricorn, a difference of 14 minutes.

The computer gives a midheaven of 6 degrees, 55 minutes Scorpio, a difference of 26 minutes.

The Los Angeles example:
The Sidereal time for the chart is 6:04. I found 6:04 on page 46 of the AFA Placidus Table of Houses. I skipped to page 47, where I found a table for 6:08. It gave these results:

MIDHEAVEN: 1 degree, 50 minutes of Cancer
11th house: 3 degrees, 11 minutes of Leo
12th house: 3 degrees, 43 minutes of Virgo

ASCENDANT: 0 degrees, 50 minutes of Libra
2nd house: 28 degrees, 4 minutes of Libra
3rd house: to be 28 degrees, 33 minutes of Scorpio

The computer gives a midheaven of 1 degree, 37 minutes of Cancer, a difference of 13 minutes.

The computer gives an ascendant of 1 degree, 29 minutes of Libra, a difference of 41 minutes.

Can better hand calculation be done? Of course. The "fudge factor" is a cover for the interval between midnight GMT & birth, combined with the shift westward from London to the birth location. If you want that, here they are:

Add ten seconds for every 15 degrees west of London, add 20 seconds for every hour past midnight.

Then you will need to interpolate the chart's sidereal time to the standard sidereal times shown in the table of houses, as well as interpolate the exact latitude of birth. New York is really 40 degrees, 45 minutes north of the equator. And remember that I rounded the sidereal time shown in the ephemeris. Do all this & you should be within a few minutes of a degree of the computer.

But for those of you completely in a fog, this should help.

The Astrology Center of America

207 Victory Lane, Bel Air, MD 21014
Tel: 410-638-7761; Toll-free (orders only): 800-475-2272

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