The Part of Fortune is not a celestial body or an angle: it is a calculation. It comes out of three pieces the chart already has, the Ascendant, the Sun and the Moon, combined in a formula inherited from ancient astrology. There is nothing there to point a telescope at, and nothing there the three do not already say.

That does not make it useless, but it changes what you can expect from it. It is a compact way of asking one question: where do those three pieces get along? Anyone selling it as “where your money is” is promising what the calculation does not contain.

The Part of Fortune is the phase of the Moon drawn from the Ascendant, and this is an identity, not an approximation. In a day chart the formula is Ascendant + Moon − Sun, and the arc separating the Part of Fortune from the Ascendant is exactly the distance between the Moon and the Sun: the Moon phase. Checked across a hundred thousand cases, with floating-point error and nothing else.

At the New Moon, at 0°, the Part of Fortune sits right on the Ascendant; at the waxing crescent, 45° from the Ascendant, still on the rising side; at the First Quarter, at the bottom of the chart, 90° from the Ascendant; at the waxing gibbous, 135° along, coming up to the Descendant; at the Full Moon, at 180°, on the Descendant, opposite the Ascendant; at the waning gibbous, 225° along, moving into the top of the chart; at the Last Quarter, at the top of the chart, 270° from the Ascendant; and at the waning crescent, 315° along, on its way back to the Ascendant.

Anyone born at New Moon has the Part of Fortune right on the Ascendant; anyone born at Full Moon, on the Descendant. Two people with the same Ascendant and the same Moon phase have the Part of Fortune on the same degree, even if they were born decades apart.

Ancient astrology uses two formulas, and picks by where the Sun is:

• Day chart, Sun above the horizon: Ascendant + Moon − Sun.
• Night chart, Sun below the horizon: Ascendant + Sun − Moon.

The two give points mirrored around the Ascendant, and the distance between them is twice the Moon phase, which is to say, it does not depend on the Ascendant at all. Swept hour by hour from 1930 to 2030, across 876,600 instants:

The two formulas sit 90.67° apart on average and fall in different signs in 91.8% of cases; they coincide only at New and Full Moon, 0.55% of hours, and are opposite at the two quarters, 0.56% of hours.

Nine out of ten. A site that always uses the day formula, and many do, gives a different sign for almost every night birth. This site uses both, and picks by where the Sun is, as the classical formula requires.

With the Part of Fortune in Capricorn, things move when you take on the whole responsibility. It is the place in the chart where half does not pay. A project you own end to end works; one where you are part of a diffuse machine does not. This usually shows up early, and is usually mistaken for excessive control.

Time is the other component: this arrangement pays off over a long horizon. Many people with this position spend their twenties feeling they have fallen behind and find out at forty that they were slowly building something the others do not have. It is the chart that punishes haste most.

This position is recognisable by the size of the responsibility you carry well. These are concrete signs, the kind you recognise in your own week:

• You get more done when the result depends on you alone.
• You took on responsibility early and it turned into a practical advantage.
• Your achievements look slow up close and solid from a distance.
• Confused structures stall you more than difficult tasks do.
• Someone has called you controlling, in a situation where you were only answering for the whole.

Notice what that list does not say. It does not say you are controlling, it says that your combination pays off when the responsibility is whole and the horizon is long.

Every piece that depends on the Ascendant needs the birth time. The Part of Fortune needs it for a second reason that is its own: the time decides which of the two formulas applies. If the Sun was above the horizon, it is one; below, the other, and we have just seen what that switch does.

Measured in four cities, from Belém to Reykjavík, across a full year hour by hour:

• half of all charts are day charts: from 49.9% in São Paulo to 51.4% in Reykjavík;
• 8.3% of birth times fall within thirty minutes of sunrise or sunset, and that is exactly the stretch where half an hour of error switches the formula;
• 1.39% fall within five minutes.

Anyone born near dawn or dusk whose birth time is not written down precisely should distrust their own Part of Fortune before any other piece of the chart.

The Part of Fortune is not money, and it is not luck. Nobody has “guaranteed success in Capricorn”. The calculation describes a fit: your three pieces work under complete responsibility, and that is as heavy as it is effective.

And it adds no new information to the chart. Being derived from the Ascendant, the Sun and the Moon, everything it says was already in them, what it offers is the summary, not an extra fact. Someone with the Part of Fortune in Capricorn and the Sun in Gemini often blames themselves for not being light, without noticing that the seriousness is precisely where the chart pays off.

A limit said out loud, because it is part of reading seriously: none of this is prediction. Astrology describes tendency and gives vocabulary for what a person already lives, it does not determine what will happen, and nobody should be selling that.

And the questions that come up most on this subject, with the short answer: