The measurement first
Checked at noon for every year from 1930 to 2035, the Sun on 7 July occupied between roughly fourteen and a half and just under sixteen degrees of Cancer. Fifteen degrees, the exact midpoint of the sign, sits inside that band in most years.
It is worth stressing that this is the full spread and not a mean. There is no year in the sample where the Sun on this date was at ten degrees, or at twenty. Across four generations the figure stays inside a window narrower than the width of a single face.
Six hours out, one day back
The Earth completes its orbit in about three hundred and sixty five and a quarter days. A common calendar year is three hundred and sixty five, so it finishes a quarter of a day early and the Sun arrives at any given longitude about six hours later by the clock than the year before. Three common years in a row accumulate close to eighteen hours of lateness.
The fourth year adds 29 February, which pushes every subsequent date one day later in the count and so pulls the solar longitude back by roughly a day's worth of motion, a little under one degree. The accumulated lateness is wiped out and the cycle starts again. What survives is a sawtooth of well under two degrees.
The correction to the correction
A quarter of a day is not exact. The tropical year is closer to three hundred and sixty five days and just under a quarter, so adding a leap day every four years slightly overcorrects. The Gregorian rule fixes this by skipping the leap day in century years not divisible by four hundred, which is why 1900 had no 29 February and 2100 will have none either.
That is why the sampled range holds steady rather than slowly sliding. Without the century rule this birthday's degree would creep by about three quarters of a degree every hundred years, which would be visible over the span of recorded astrology.
The same arithmetic answers the cusp question for this date. Fifteen degrees of Cancer is fifteen degrees from Gemini and fifteen from Leo, which at this rate of travel is about sixteen days in each direction. Since the ingress moment itself only wanders by around a day and a half between years, there is no reading of the calendar under which this birthday is near an edge. It is as far from both boundaries as a date in this sign can be.
What the steadiness is not
It does not mean the Sun is at the same place at the same clock time each year, only that the longitude on this calendar date stays in a tight band. Within one 7 July the Sun still advances close to a degree from midnight to midnight, so the hour of birth shifts your figure slightly.
It also applies to nothing else. The Moon can be in either of two signs across a single day here, and the ascendant covers all twelve in twenty four hours. The stability belongs to the Sun alone, which is exactly why the widget above asks for your hour and birthplace before reporting a degree and a margin from the nearest boundary.
One oddity of Cancer is worth naming while the subject is motion. The sign is ruled by the Moon, which is the fastest moving body the tradition uses, so the ruler of the chart travels about thirteen degrees a day against the Sun's one. In every other sign the ruler is slow enough to be shared across a run of birthdays. Here it is the single most variable thing in the chart, which is one reason two people born on the same 7 July can have very little technical common ground.
Questions people ask about this
What sign is 7 July?
Cancer, with no ambiguity. The date lies roughly halfway between the Cancer ingress in late June and the Leo ingress in late July.
Why is the solar degree so consistent?
Because the six hour annual drift and the leap day correction very nearly cancel over a four year cycle, and the century rule stops the small remainder accumulating.
What is the exact degree for my year?
It falls somewhere between about fourteen and a half and sixteen degrees of Cancer at noon. The widget above computes your own figure from the year, the hour and the birthplace.
Is fifteen degrees significant?
It is the midpoint of the sign, and older sources treat it as the point where a sign is least influenced by what lies either side. That is traditional interpretation rather than a measurable property.
Which face of Cancer is this?
The second, running from ten to twenty degrees. Mercury holds it in the Chaldean order and Mars holds it in the triplicity scheme through Scorpio.
Does the degree change within the day?
Yes, by about a degree from midnight to midnight. That is small compared with a face but enough to matter when a chart is measured precisely.