Lots and the Part of Fortune
Your chart holds more than planets. It also holds points nobody can see in the sky, because they are not bodies at all: you get them by measuring the distance between two things in the chart and laying that distance out again from the Ascendant. The Hellenistic tradition calls them Lots, and the best known of them is the Part of Fortune.
The name misleads, so let us clear it up straight away. A lot here is not blind luck, not a lucky break, not a fate already written. It is the share that falls to you: the portion of life the chart hands you in a given area, the ground you move on. A Lot is an index, a measuring device, not an oracle handing out prizes or announcing disasters.
The Part of Fortune measures the relationship between the Sun and the Moon at the moment you were born, read from the exact place you were born. The Sun says what lies at the bottom of your character, the Moon says how that gets distributed through ordinary days, and the Ascendant says which point on Earth you are looking from. The Part of Fortune holds the three together and points to where you most naturally find ease and expression. The Lot of Spirit, its counterpart, covers instead what you do deliberately and on purpose, and in the tradition it is the point zodiacal releasing starts from.
Like the lunar nodes, the Lots do not tell you what will happen. They tell you where you sit comfortably and where you have to supply the intention yourself. The chapters look at the mechanism first, meaning how a Lot is built and why the formula changes depending on whether you were born by day or by night, then at the Part of Fortune, and finally at the Lot of Spirit.