The straddling position
At noon in each year from 1930 to 2035, the Sun on this date fell between about eight and seven tenths and just over ten degrees of Cancer. Nine and a half is the middle of that band, and the ten degree mark sits inside it rather than outside.
So in most of those years the position is under ten and in a minority it is over. The sign is Cancer throughout, since the nearest boundary is more than a week away in either direction, but the face the Sun occupies is year dependent in a way the sign is not.
Noon serves as a common reference point across the years. Because the position sits so close to an internal line, though, this is one of the dates where the choice of hour is not entirely cosmetic.
What the two bands differ in
Below ten degrees the Sun is in the first face of Cancer, which the Chaldean order assigns to Venus and the triplicity scheme assigns to the Moon. Above ten it is in the second, which the Chaldean order assigns to Mercury and the triplicity scheme assigns to Mars by way of Scorpio.
Nothing else moves. Cancer stays cardinal water with the Moon as its domicile ruler, and the elemental and modal readings are untouched. Only the face ruler swaps, so the difference is a shading rather than a different sign.
The tradition reads Venus over the opening of a water sign as softening, and Mercury over its middle as more analytical than the sign's own tenor. Under the triplicity scheme the Moon doubling with the sign ruler is read as intensifying it, and Mars as sharpening it. All four are conventions rather than findings.
How to settle it for yourself
The deciding factor is the year, and to a smaller degree the hour. Common years push the position a quarter degree further along for the same date and leap years pull it back around three quarters, so the value walks up and down within that band on a four year cycle.
Because the position can sit within a fraction of a degree of the line, the hour of birth can matter too, and so can the time zone that converts local clock time into a universal instant. The widget above handles all of that from your year, hour and birthplace.
What is settled either way
Cancer holds without qualification. The tradition reads it as protective and retentive, opening a season by instinct rather than plan, and that reading is the same whichever face the Sun landed in. It is also shared with everyone born within a month of you in any year.
The date does not reach the Moon, which may be in one of two signs depending on the hour, or the ascendant, which turns through all twelve in a day. Those are the placements that separate two people born on this date, and both need a birth time.
The slow planets do come with the date. Saturn, Uranus, Neptune and Pluto stay in a sign for years, so the year alone places them, and they are held in common with everyone born across the same period. They describe a background, not a person.
Questions people ask about this
Is 1 July definitely Cancer?
Yes, at noon in every year from 1930 to 2035. The Sun sits near the middle of the first third of the sign, more than a week from either boundary.
Which decan does 1 July fall in?
It depends on the year. The noon position runs from about eight and seven tenths to just over ten degrees, so most years fall in the first decan and a minority in the second.
What decides which side I am on?
Mainly your year, because leap years pull the position back and common years push it forward. When the value sits within a fraction of a degree of the line, the hour and time zone decide as well.
What changes between the two decans?
Only the face ruler. Venus gives way to Mercury in the Chaldean order and the Moon gives way to Mars in the triplicity scheme, while the sign, element and domicile ruler stay put.
Is a position on the line a blend of both?
No. A longitude falls in one band or the other at any instant. Being close to a line means the answer needs a calculation, not that it is mixed.
Does this affect my sun sign reading?
Not at all. Cancer holds either way, and the decan is a narrower layer beneath it rather than a competing verdict.