While doing readings at Dose Market last weekend, a woman sat down and asked: What happens when people don’t know what time they’re born?

It’s a good question. And the answer is that the astrologer then has to take what he does know – the date of birth and place of birth – and try, through trial and error to figure out the time of birth. It’s important because the time determines the degree of the Ascendant, also known as the rising sign. In ancient astrology, the Ascendant was sometimes called the “helm,” because it was believed to be so important that it served as a guide for a person’s life.

To illustrate the difficulty, I’ve chosen a person we’re all very familiar with – Tom Cruise – but whose birth time has never been published or discovered. If you look on the web, the charts that are posted for Cruise use noon as the time of birth, which is the standard astrological convention when you don’t know the real time.

Before I talk about how I chose this particular time, let me just add that: FIGURING THIS OUT IS VERY DIFFICULT. There are 12 signs and 360 potential degrees to choose from, so there’s a lot of pushing and pulling the planets around the chart to see where they may work the best. Of some help is the fact that while the Moon moves at around 13 degrees per day, the degrees of the rest planets are stable. It’s just the houses and where the signs fall that we’re trying to determine. That said, below is the chart with a birth time that I’ve landed on for the actor.

So why, out of all the twelve signs, did I choose this particular time, which gives the actor Libra as the ascendant? First of all, remember that every sign has a ruling planet and for Libra that planet is Venus. When we look at Venus’ placement, we find it in Leo, which makes a lot of sense regarding Cruise’s “star quality”. Quite simply, whether you like him or not, he shines, and with both Venus and the Moon in Leo, he shines a lot. By using Libra as the ascendant, his Venus and Moon are suddenly in the 10th house, the midheaven, the most visible placement in the chart. Does that make Libra the only candidate? Not at all. I also considered Scorpio, for his secretive qualities, as well as Leo, for the qualities I’ve already mentioned. But in the end, Libra is the sign that best puts Cruise’s star potential in the chart position in which it has the most potential for fulfillment.

One thing that must be said about the chart is that there is a lot of power. Moon and Venus in Leo, the most dramatic and royal of signs: enormous needs for attention,  love and respect. A sense of drama is high: remember Cruise jumping up and down on the couch during the Oprah show? Venus, also in Leo, reinforces the need of the Moon and adds a magnetic quality. With the placement of both high in the chart – due to the Libra ascendant – these needs are played out dramatically in the world, in full view, so to speak. With Mercury in Gemini, we can anticipate a high degree of verbosity, there are a lot of ideas being tossed around in his head. As the chart stands, both Venus and Mercury make supporting aspects to the Ascendant: the image is everything and everything that is done protects the image. Speaking of protection, the Sun in Cancer adds both a layer of protection – think of the crab – and a sensitivity. In combination with the Leo Moon: enormous pride. There’s more that could be said, of course. But let’s look at the Cruise’s natal chart for the time I’ve calculated it against his chart for the current year.

What stands out here is Saturn (circled) almost exactly on the Ascendant and opposite the 7th house of relationship. Saturn on the Ascendant in any given year points to difficulty, a restriction, a loss, a reality check for the individual, a category in which being left by your wife belongs. How will Cruise deal with it? His Ascendant for the year is in Scorpio, a sign well known for its skill in rejuvenation, self-healing and resurrection. In other words, don’t worry too much about Tom: he’s going to be fine.