This is bit of a dump as there have been requests for this information. Therefore, I just want to get it out here, while I work on something more structurally as well as visually pleasant for good readability.

On this page, I will try to describe in reasonable detail and depth the features you can expect to find in our free astrology software Astrocalc 6.5, presented in a reasonable order for a student of astrology.

As Astrocalc is actively developed, it may bring changes and amendments not immediately reflected here. The first part below describes some basic features and characteristics included and further down more specific astrological features will be presented in greater detail.

Atlas module with Time Zone corrections
Our own developed Atlas covers over 200 000 places worldwide with geographic coordinates and handles time zone corrections including DST, also valid for historical dates. It is actively maintained and regularly updated to reflect time zone changes due to decisions taken by various governments. In case you disagree with geographical data, you can edit values, add new custom places and associate them with a time zone. All changes you do are persistent and will not be lost when you update/upgrade the program or just the atlas.

5000 Year Ephemeris and Accuracy of calculations
Astrocalc generates accurately calculated positions for the period from BC 2500 to AD 2500 using directly calculated algorithms that obviates the need for very large, pre-calculated disc ephemerides and allows calculations of Declinations and Latitudes.

For the outer planets (Jupiter to Pluto), we use a set of planetary algorithms calculated for us by John Dice. They are based on the  A.P.A.E. Volume 22. Our calculations give 1 minute accuracy over a 5000 year period (2500 BC to 2500 AD).

In fact, in practice the accuracy of all planetary calculations will normally be within a few seconds of arc – but note the comments below on time problems and the difference between true and apparent positions.

Adjustments to the algorithms used by NASA and others are always being made, but the changes are usually very small indeed. The only possible exceptions to this would be with Neptune and Pluto whose orbits have not yet been accurately observed over a full revolution. Even so future changes will have no noticeable effect on the calculated values over the past 400 years.

The values for the Asteroids (including Chiron) are obtained using mean values. On average, these will be within 1 degree of longitude. Note that Chiron has only been accurately observed over 1/3 of a revolution. Published ephemerides for Chiron also rely on unverified and inconsistent observations prior to 1978 and some use inappropriate integration periods. When ephemerides claiming 1 minute accuracy differ from current observed values by as much as 20 mins then no ephemerides can be regarded as better than 1 degree in accuracy! In fact, calculations involving Chiron are so sensitive to small changes (the butterfly effect) that historical calculations have to be treated with caution.

The values for the hypothetical planets are based on hypothetical algorithms.

True and Apparent Positions
Astrocalc 6.5 supports both True and Apparent positions by optional setting. ‘True’ positions are the instantaneous positions of the planets calculated as viewed from the centre of the Earth. They take no account of the time it takes for light to reach the Earth. Nor do they take account of any bending of light that may occur when a planet is near the horizon. Thus, when you see the Sun or Moon rising or setting they may in fact be below or above the horizon.

If you choose the ‘Apparent’ option, the program will calculate positions taking account of the time that it takes for light from the planet to reach the Earth. For the Sun, this is about 8 minutes so that True and Apparent positions will differ by about 20 seconds of longitude (1/3 min). The positions of the other planets, apart from the Moon which is too close to be affected, will differ by varying amounts depending upon their orbital speeds and positions.

For really high accuracy with Apparent positions, you would also take account of the geographical latitude and the height above sea level, though the largest variation would probably be caused by light refraction on planets near the horizon.

As with other calculations (e.g.  the Node), the use of the word True does not mean that the calculations are better, merely they are different. Your choice in this matter will depend upon how you view the action of ‘planetary’ influences. Are they instantaneous/synchronistic? In which case the True positions would be correct. Or do they operate at the speed of light? In which case the Apparent positions are correct.

For most practical purposes, and where birth times are not known to a closer degree than 5 or 10 minutes, it probably does not matter which method you use. However, beware of techniques that call for ‘great’ accuracy and yet ignore these potential problems.

This is the difference in seconds between Terrestrial (TT) and Universal (UTC) Time, where the latter in practice equals GMT. This is a relatively new factor involved in modern time keeping. However, even if awareness of its existence as a force of time goes as far back as with Ptolemy around 150 AD, still it was not seriously researched in connection with time keeping until the middle of the 20th century. As research is relatively young and this involves a high degree of complexity, there have been several algorithms presented over the years by various astronomers of which 8-9 have earned recognition by publication and of these have 2-3 come to be more respected than others. One of these, developed by Espenak and Meeus, is used in Astrocalc and as far as we know at this point in time, no other astrology program uses the same. The impact of DeltaT on modern time charts are very minor, but of course just as when aiming with a rife the further away the target is the bigger impact has an even small deviation, hence its importance shouldn’t be underestimated when it comes to use of e.g. progressive techniques. Otherwise, it’s mostly when doing historical charts you may notice a difference depending what algorithm is used and its degree of accuracy. Is our algorithm the most accurate? We cannot claim that but it is one that is built on the latest available research and observations.

Chart Wheel
All planets and most points calculated by the program can be displayed in the chart wheel (currently, with exception of Fixed Stars, some Arabic Points and Midpoints that only is shown in lists) and you have the option of showing a planet/point but without any aspects to it. Similar options exist for all lists whether on screen or printed.

The Chart Wheel can be displayed as a single, bi- or tri wheel, and has a rich range of settings to affect what is shown.

Colours Options
A unique feature is the way that the planets take on the colours of the signs – this gives immense clarity and readability to the chart – no problems determining the sign of a planet on a sign cusp. If you like fixed colours for each planet, no matter which sign it’s found in, Astrocalc includes a rich option for colour setting. This also includes the ability to create pre-set colour profiles, of which 4 are included by default.

Also, note that by default Astrocalc will draw the chart wheel on screen against a black background. Most other software have as default to use a white background, as when printed on paper. In our opinion, a black background gives a crisper and more visible chart, and is less tiresome for the eyes if studying it a prolonged time. If you prefer a white background, it can be changed swiftly and permanently at several locations with a pre-set profile defined by the Colour Options.

Chart Design
Many of the items shown in the chart wheel can be defined using the Chart Design and other screens. This includes some colours, symbols, the type and thickness of various lines, the use of aspect indicators (these appear halfway along the aspect lines), the size of symbols, etc.

Install in any of 4 Languages available
Astrocalc 6.5 is currently available in 4 languages (English, Norwegian*, Spanish*, Swedish*), although the ones marked by * are not 100% complete at this point in time. We decided to include them anyway to make the program more available and useful for people not fully comfortable with the English as alternative language. The status for Spanish, Swedish and Norwegian are about 80%.

3 inbuilt methods of Interpretation
The 3 inbuilt interpretation methods are Sorted Remarks, Link Phrases and the Block Text facilities for Natal-, Transits Text etc. In addition, there is the Structure Analysis method from France and Ascara from Germany, and although they don’t produce any text, they still produce useful information that is relatively easy to learn interpreting.

The Block Text method has 3 variations and comes loaded with editable text, Wheel Text, Transits Text and Synastry Text. From start the Wheel Text method comes with our Natal Text, which contain about 40 000 words covering Planets in Signs, Planets in Houses and Aspects between Planets.

Wheel Text can be used wherever a chart is calculated and displayed in a wheel. The program also includes a special editor where you can not only extend the text but also copy and create new text files based on the present ones as a template. This way you can easily build a set of text adopted for not only different kind of wheels (e.g. progressions, returns) but also for different characteristics of charts (e.g. Teenagers, Women, and Karma etc.). You can of course also print out the interpretations.

Sorted Remarks is primarily intended for students or those who like to mark up their reports at the computer with the Chart Wheel displayed. It allows you to categorise your remarks under various headings such as Character, Mentality, Recreations, Love & Marriage, etc.  and have your notes automatically sorted under the headings.

Link Phrases has text that consists of key phrases which, when joined together, give the essential interpretation using the basic principles of the planets, signs and houses as well as aspects. Thus, for someone with the Sun in Aries in the 1st House, the text displayed would consist of a sentence made up like this; a text snippet for the sun, then a link phrase, a snippet for Aries, a link phrase and finally a snippet for the 1st House. With the Aspects, a sentence is constructed using the Planet text, the Aspect text plus the text for the Planet that is being aspected. It’s a very simple yet powerful way to produce vigorous interpretations.

Furthermore does the program has a rich set of options and settings allowing you to change things like Orbs, Colours, Zodiac, Calendar, Aspects to use etc. etc. Alsoincludes our Harmonics Tutorial to give you a taste of Harmonics, which are described in more detail further down.

Astrological specifications

Natal chart calculations and sensitive points
To begin with, everything starts with the Natal chart calculations – the necessary base all other routines are drawn upon – involving the 9 main planets, the 4 major asteroids Ceres, Juno, Pallas and Vesta, plus Chiron. Furthermore, included are also calculation for the so-called Transneptunians (Cupido, Hades, Zeus, Kronos, Apollo, Admetos, Vulkanus and Poseidon), displayable with symbols in the chart wheel.

Transneptunians + Black Moon + Lilith, gives the positions of the hypothetical Isis/Transpluto, the Hamburg Transneptunian planets, the Black Moon and Sepharael’s Lilith. All of these points can be shown in the chart wheel.

Lunar Phases gives the times and dates of eclipses, full, new and moons and the quarter and three-quarter phases; also aspects to natal and progressed charts. Also includes Sun/Moon Angles, which gives you the times and dates in any year when the Sun/Moon Angle is the same as at birth.

Other sensitive points

Fixed Stars: The program includes 72 fixed starts, not currently displayable in the chart Wheel.

Arabic Points: Included by default are 28 point, but you can indeed make your own additions to this list.

9 House systems

Chose from 9 different house systems, Equal, Placidus, Koch, Regiomontanus, Porphyry, Campanus, Alcabitus and Whole Sign Houses, to use in the program. The houses can optionally also be divided with faint bisectional or trisectional house lines. Optionally, you can also have reversed houses.

In addition, included is also a Tables of Houses generator. With the Tables of Houses you can display and print your own accurate tables of houses for any valid latitudes anywhere in the world using any of the 9 available house systems.

The program also include some routines to do basic Horary, Hindu and Chinese Astrology, a routine to calculate ingresses for the Sun and Moon, and the time data can be imported into a chart wheel by a simple click.

For natal charts, there is also a Huber module included that cover most but not all of the Huber Schools techniques. More detail below.

Create your own Ephemeris showing the sidereal time, day of the week and the planetary positions etc. More details below.

Transits and Progressions to the natal chart.

(Exact Date) Transits can have a span of being either monthly or daily and give you fast and accurate exact date transits over various periods of time.

You can choose any start date and the program will calculate selected aspects showing the exact date for the transit to occur, plus an orb period of 1 degree influence when a transit takes place (where this exceeds 2 days). This can be on a monthly basis (from 1 to 60 months at any one time) either excluding the Moon, or on a daily basis (from 1 to 35 days) including the Moon.

The house positions of both planets are also shown and output can be sent direct to printer as well as screen.

The [Next] menu bar option allows you to select the next batch of transits by one simple click of the mouse. With the Transits Text file, you can also show on screen or print out a full text forecast.

Apart from the ordinary Daily and Monthly transits, the ability to do transits to charts other than the natal chart and shows aspects to house cusps, plus the ability to calculate and display current daily transits (i.e. transits which are occurring as of now rather than those to any natal chart).

The extended transits includes the ability to do them to other than the natal chart and show aspects to house cusps, plus the ability to calculate and display current daily transits.

You can also have the result output to an ASCII format file to store on disc and there is a powerful mutual transits search option, which allows you to find distant aspects – e.g. conjunctions, oppositions, etc. between the outer planets.

A Timed transits option, which gives you the time when the transit occurs, not just the date (only approximate with slow-moving planets).

As for interpretation text it adds text of about 15 000 words covering Transits. The text is fully editable and you can extend the text and give it your own touch of words.

The Day-for-a-year Progressions includes 2 variations. The first one, often referred to as Secondary Progression, uses the Age and gives the progressed positions with the birth details progressed on by the Age. Optionally you can set the date to use, instead of the Birth date. The second uses the Perpetual Noon/Midnight Date option and method of calculating progressions (Solar Arc added to the MC – i.e. Primary Directions), as used by the Faculty of Astrological Studies.

Both variations show mutual aspects and natal to progressed including the actual orbs, applying and separating aspects, together with lunar aspects by month. Select the next year by simply clicking the mouse button.

(Custom Degree) Arc Directions. Enter a value in degrees and this is then used, together with the specified age to calculate new planetary positions. By tradition, 1 deg. is typically used but you can adjust this value by decimal as it pleases you. Aspects between the new Directed Chart and the Natal positions are also shown.

True Solar Arc. Enter the age and the program will calculate a chart based on the True Solar Arc of the Sun. This means that all planetary positions are advanced by the distance the Sun has travelled. Aspects to the Natal positions are shown.

Naibod/Radix. All planetary positions are advanced by the mean value of the Sun’s daily motion multiplied by the Age, except for the Moon where the Moon’s mean motion is used. Aspects to the Natal positions are shown.

Daily Progressed Angles. Enter a date and the program will calculate a Day-For-A-Year Progression as with the method included in Basic Edition, except for the angles. These are calculated on the basis that during each progressed day they travel through about 361 degrees instead of about 1 degree. The results will therefore only be the same on birthdays. Mutual and natal to progressed aspects are shown, plus lunar aspects by month.

Tertiaries 1 and 2 This is similar to Day-For-A-Year Progressions except that the Moon is used instead of the Sun. i.e. it is Month-For-A-Year and Day-For-A-Month Progressions. Mutual and Progressed to Natal Aspects are calculated.

Transits and Progressions can also be plotted as a graphic view, where you visually can see how the transit/progression of a planet moves over time in relation to the natal planets.


This is all about relationships. We all love Love and in astrology Love is about Synastry and here you can get it all analysed!

Apart from what you have read so far, this adds Direct Chart Comparisons, Composite Charts (for groups of up to 12 persons) and the so-called Davidson Chart, a relationship composite of time, location and space. Furthermore does it includes the Trigo method that is a method for choosing your ideal partner. It also adds the ability to do Bi-Wheels and readable Tri-Wheels, list planets in the other person’s houses and more.

Direct Chart Comparison enables input of 2 charts and subsequent comparison giving the aspects between the charts and planets in houses of other chart.

The Composite Chart calculates the midpoints between 2 or more charts and the inter-aspects for the natal chart (and progressed charts if calculated). There are 2 methods used to derive at the Ascendant and subsequently layout of house system and Mc, either by midpoint as with planets or from the latitude where the relationship/event is deemed to have taken place. The latter can be accomplished by either using the Atlas or enter in values manually. Up to 12 charts can currently be used to form the composite charts.

Relationship Chart, also known as the Davidson Chart, calculates a new chart using the midpoints in time, location and space. Thus if the latitude of the 2 charts are 60 N and 40 N, then the new chart would be calculated for 50 N and the same algorithm is used with the longitude, time and date of birth. Up to 12 charts can be used as basis for the new one.

The Trigo Method, named after the Spanish astrologer Juan Trigo who has developed it, is a test in 2 parts. The first is of a person’s facility for couple life. The second evaluates how 2 people relate to each other. Within each test, the rules are applied and points added positive and negative. Brief textual descriptions are then selected according to the various scores.

The Synastry module also adds interpretation Text for Direct Comparison between 2 charts, and the already included text for Natal Charts can easily be adjusted and adopted for use with Composite and Relationship charts.

Wait there is more coming up, Harmonic Calculations and Chart Analysis, Midpoints and Planetary Returns for not only the Sun but all planets. Zodiac Calendar, Lunar Calendar, Sun/Moon Ingresses.

Returns of Solar/Lunar and all major planets
allow you, depending on type of return, to enter the age in years or a date and a return chart will be calculated and displayed in a wheel. The chart can also be relocated.

In the case of the Sun, the date and time will correspond to the birth date plus the age, adjusted so that the Sun’s new position corresponds exactly to the birth position (hence the name Return). As for other planets, except for the Moon, the procedure is similar except that the return doesn’t necessarily appear close to the birth date.

With the Moon, which returns to its natal position every month, the program uses the date entered to calculate the nearest Lunar return, and can be in the future or the past.

There is also a relocation option if you want to relocate the chart from your natal birthplace to where you are at the time of the return, which simply involves picking the place from the Atlas or one of your own defined Quick Places.

You can optionally also apply a correction by precession, which ‘fixes’ your natal positions for the Sun and Moon as if they were in the Sidereal Zodiac and then adds a further correction based on the age or date entered, taking in to account the subsequent precession of the planets since birth.

Returns can also be used in Bi-Wheels and Tri-wheels.

Aspects to natal chart as well as aspects within the return charts are shown. You can step back and forth between returns by selecting the Previous/next option by one simple click of the mouse. The bi-wheel option also allows for comparison of Return Charts, or for Return Charts with Progressed or Harmonic Charts.


Includes Natal Planet Aspects to Natal Midpoints, Transits to midpoints and Solar Arc Directions to midpoints. Orb and dials can be changed and various sorted lists of midpoints obtained.

Midpoint Trees is a calculation module specially written by Mike Harding, plus a manual (included in the Windows user manual) explaining the use. Prints out 3 pages, the first being the trees, the second a sorted list of direct and indirect midpoints plus an aspectarian, the third being the Cardinal, Fixed and Mutable sort. The Trees can be viewed on-screen. As taught by the Faculty of Astrological Studies. A must have for all serious students of astrology.

Basic Harmonics give you multiple lists of harmonic positions and single harmonic charts with aspects. Also Harmonic Contacts between the various harmonic charts.

Harmonic Chart Analysis Uses Harmonic orbs, measures every aspect’s strength, gives aspect-strength for each planet, reports all 3-planet configurations with strength, user options for size of orbs, selection of aspects, etc.

Harmonic Chart Analysis with Progressions Carries out the basic analysis already available, on both natal and progressed charts, enabling an in-depth look at a person’s current personality and life-situation.

Decimal (dated) Harmonics – Enter a date and the program uses this to calculate a ‘harmonic’ number based on the difference between this and the birth date. New harmonic positions are then calculated with this number in the same way as usual.

Planetary Harmonics (as calculated by John Greig). The natal positions of the planets are divided into 360 degrees to get ‘harmonic’ numbers. E.g. if the Sun is at 0 degrees Libra then the harmonic number would be 2. This harmonic number is then used to multiply all the positions of all planets apart from the Sun and calculate new positions. This gives the Sun planetary harmonic chart. Similarly with other planets.

Tables of Houses Generator enables you to display and print your own accurate tables of houses, using any of the 8 House systems included, for any valid latitudes anywhere in the world. Choose any time interval from 4 to 60 minutes. Unlike published tables of houses where intermediate cusps are given to the nearest degree, the program gives all 12 houses with cusps to the nearest minute of longitude. This function is ideal for teachers, students and reference purposes.

The Ephemeris Generator will allow you to display on screen or send to printer an ephemeris showing the longitudes, declination/latitudes, distance values and heliocentric positions of the planets for any month from 2500 BC to 2500 AD. You can choose between Noon or Midnight Ephemeris and Calendar to use, Gregorian or Julian.

The Huber module is composed especially for you who only are interested in Huber Astrology and doing Natal Charts according to the methods of API. It allows you to do astrology according to the methods of API, following the approach of Huber School. It will calculate and draw all the Natal, Place, House and Moon Node charts, display aspects, perform the Dynamic Calculations, Age Point progressions, calculates and shows the Invert/Balance Points and Low Points, etc. and printouts of course.

In accordance with the Huber School directives, only the 9 planets are used and Koch houses, together with standard Huber colours and orbs.

With the Zodiac Calendar routine, you can create the ideal Christmas/New Year or Birthday Present as it enables to produce yearly printed Zodiacal calendars, or single months. Shows the dates and times of the Sun Ingresses, all Lunar phases with dates, times and positions and planetary information regarding changes in direction (Mercury to Pluto), etc…

  • 1 A4 sheet per month, with 1 line per day
  • Shows all the phases of the Moon, together with date, time and position.
  • All the ingresses of the Sun (when it changes sign), with date and time.
  • All dates when any of the planets (Mercury to Pluto) change sign.
  • All the dates when any of the planets change direction (from direct to retrograde or vice-versa) plus the positions when they do so.
  • In addition, at the beginning of each month the positions of the planets are listed.
  • All positions shown in degrees and minutes, all times in GMT.

Optionally print a designable front page to include in a nice binding, and produce a calendar in any of the languages English, French, German, Dutch, Spanish, Swedish, Norwegian and Italian.