A lopsided but real split
Leo starts at one hundred and twenty degrees of ecliptic longitude. In most years the Sun crosses that point during 22 July or the small hours of the twenty third, which is why the great majority of noon births on this date come out Leo. In a handful of years the crossing waits until later in the day and the tally goes the other way.
The reason it is not fixed is the tropical year, which runs about a quarter of a day longer than the calendar year. Each year the ingress arrives roughly six hours later on the clock, and each leap day pulls it back about eighteen hours. Follow this one boundary across a decade and it covers something like a day and a half before it returns to where it began.
Where the Cancer answers come from
Two conditions produce them. The first is the birth year: the early and middle part of the last century placed the ingress later on this date more often than recent decades do. The second is the hour, because in the borderline years the change falls somewhere inside 23 July and a birth at three in the morning is Cancer while a birth at ten at night is Leo.
This boundary also sits close to aphelion, when the Earth is at its greatest distance from the Sun and moving most slowly, so the Sun takes about thirty one and a half days to cross Cancer against about twenty nine and a half in the signs near early January. That extra length gives the entry point more room to drift, which is why late July boundaries move more visibly than the winter ones.
One moment worldwide, different local dates
An ingress does not happen at a local time. It is a single instant for everyone, and the only thing that changes from place to place is what the clock reads. When Leo begins at 02:00 UTC on 23 July, that same instant is ten in the evening on 22 July in New York and seven in the evening in Los Angeles, so an American born on the evening of the twenty second is already Leo.
Failing to make that conversion is the most common way a sun sign gets written down wrongly, and it accounts for a great many of the disagreements people have about their own charts. The widget above takes the year, the hour and the birthplace, resolves them to one instant, and tells you how many hours from the boundary you were born.
Cancer and Leo, and the cusp that does not exist
Cancer is cardinal water ruled by the Moon, read as protective, retentive and attached to origins. Leo is fixed fire ruled by the Sun, read as expressive, proud and centred on what it makes. They are ruled by the two lights, which is a real link and not a decorative one, and both are described in terms of loyalty and of taking things personally. The difference the tradition presses on is direction: Cancer keeps things safe and Leo puts things on display.
What you will not be is a mixture of the two. At any instant the Sun occupies one degree of longitude and that degree sits inside a single sign, so half an hour either side of the change you are entirely one or entirely the other. The Cancer Leo cusp is a label for a birth record nobody has finished reading. And if the answer turns out to be the sign you did not expect, it moves one placement. Your Moon, your Ascendant and everything else in the chart are unchanged.
Questions people ask about this
Is 23 July Cancer or Leo?
Leo in the large majority of years. Measured at noon from 1930 to 2035, ninety one years came out Leo and fifteen came out Cancer, so Cancer is uncommon on this date but not rare enough to dismiss.
Which birth years are most likely to be Cancer?
The earlier ones. The ingress has drifted slightly earlier across the last century, so births from the middle decades of the twentieth century are more likely to fall on the Cancer side than recent ones.
Does my birth time matter on this date?
In most years it does not change the sign, because the ingress has already passed by the time the day begins. In the borderline years it decides the answer outright, so it is worth supplying if you have it.
Am I on the Cancer Leo cusp?
No, because nothing sits between the two signs. The Sun holds a single ecliptic longitude at any moment and that longitude is inside one sign. The cusp term stands in for missing year, hour or place.
Why do some tables say Cancer runs to 22 July?
Because a printed range has to fix a boundary that actually moves. Ending Cancer on 22 July is a fair rounding for most years and simply wrong for the minority where the ingress falls later on the twenty third.
Is a Leo Sun at zero degrees a weaker Leo?
No. Position within a sign does not dilute it. A Sun at zero degrees of Leo is fully in Leo, and the degree affects aspects and house placement rather than the sign itself.