Computers really have revolutionised astrology. If I’d been writing this article twenty years ago, explaining how to calculate your chart would have seemed very complicated indeed. You would have needed to do some fairly fiddly arithmetic, and required several books - a “table of houses” just to calculate the Ascendant, an “ephemeris” to find out where each planet was (and to find out “sidereal time”, a kind of star time needed to calculate your Ascendant), and a book giving lists of cities with their latitudes and longitudes and time zones. And knowing whether Summer Time was in operation was largely a matter of guesswork, and frequently the cause of incorrect charts.

That is all a thing of the past. There are various sites that enable you to calculate charts online, but the one I always use is the excellent Astrodienst site. (This page should open in a new window - if you don’t have Java or pop-ups enabled, click here to access the Astrodienst site).

The site is fairly easy to use, but requires a little bit of practice - so I’m going to show you how to use the site step by step.

As an example, we’ll use the chart of Pierre Trudeau, the former Canadian Prime Minister.

His details are:

Start off by going to the Astrodienst site and on the left hand side of their home page you’ll see a link saying “Free Charts”:

This should take you to a general menu; before selecting anything from this menu, you need to enter the birth data. You have the option to do this by clicking on the relevant wording about entering data, on the right hand side of the screen:

This then brings up a data entry screen, as follows:

Enter the relevant details. Tick the “show map” box, DON’T tick the “use manual timezone” box, select “Canada” for the country from the drop down box, and enter “Montreal” for the birth town:

Click on the “Continue” button:

This will then give you a list of matching towns, together with a map showing the first one on the list. You’ll notice that this map shows the latitude (45N31) and longitude (73W34), the timezone (EDT means Eastern Daylight Saving Time), and the code “h4w DST” which means 4 hours behind GMT, with daylight saving time in operation. Notice also that the Sun, Moon and Ascendant signs are now shown for the first town on the list, underneath the person’s surname.

In this case, the first town on the list is the correct one, so select it by pressing the “Continue” button once more:

You are now taken back to the original menu. This time, however, a box saying “Currently selected Astro data” appears on the right hand side.

Now select the “Chart drawing and Ascendant” choice from the menu, and the chart is displayed:

You have now produced the chart. This chart can be printed, or you can edit the data. This site allows to you enter up to three charts - or you can register (free of charge) and use it to create any number of charts.

So, to recap: we only knew Pierre Trudeau’s birth date, time and place. The Astrodienst site told us the latitude and longitude, the time zone, and whether Daylight Saving Time was in operation on 18 October 1919 in Montreal (it was). We then produced a chart, showing the position of all his planets to the nearest minute in a table, a chart wheel showing these planets together with house positions and the Ascendant (we can see that he has Sun in Libra, a Libra Ascendant as well, and Moon in Leo), and an “aspect grid” showing which planets are making aspects to other planets.

This would have taken most professional astrologers at least half an hour to do by hand, and a beginner very much longer. The thorny question of whether Daylight Saving Time was in operation in 1919 would have been quite difficult to find out, too.