When the Birth Time Is Uncertain

The Ascendant changes sign about every two hours. So a birth time off by an hour or two may put the Ascendant in another sign, and right at the border between two signs a few minutes can make a difference. When the Ascendant moves, the whole ring of twelve houses turns with it.

To find your birth time, look at your birth certificate, hospital records or baby book, or ask your family. If all you remember is “some time in the morning,” leave it blank and add the exact time once you find it, so the Ascendant and houses you see are really yours.

What the old texts say: Ptolemy's Tetrabiblos, Book III ch. 2, opens by admitting that the most important and most troublesome thing is the birth time down to the minute. Only measuring with proper instruments at the birth gets the minute; the other tools most people use often err — sundials when their position or pointer shifts, water clocks when they clog, run unevenly or by plain chance. So he then gives a method that uses the new or full moon just before the birth to work out the degree that should be rising.

With no birth time, this app takes a position every hour across your day of birth (25 samples, covering the whole local day) and sees which signs each body was in that day. If there was one, it is shown as it is; if there were two, both are listed and marked “unconfirmed.” The Ascendant, Midheaven and houses need a birth time to be calculated, so that layer is left empty.

So without a birth time you can still read your Sun, most planets' signs and every aspect. The Moon shows two candidates more often, because it changes sign every couple of days.

What the old texts say: Book III ch. 2 makes the rising degree the starting point of the whole chart; with that starting point, the houses can be laid out.

This app works from the data you give it: what can be calculated is shown as it is, and the layer that needs a birth time is left empty until you add one.

The good thing about an empty row is that you see at a glance what was calculated and where there is no data yet. Every row it shows was really calculated. If you find the exact time later you can add it any time, and the house layer appears.

Without a time, get to know the layers that are certain: the Sun, the planets' signs, every aspect, and the Moon's two candidates — compare the two descriptions and see which sounds more like you. Once you add a time, the Ascendant and houses join in and the same chart gains a layer of detail.

What the old texts say: the text's answer is a whole set of rules — domicile, exaltation, terms and aspects — used to work out the degree that should be rising. That is a grounded procedure you can check.