Where the Sun stands
Checked at noon across 1930 to 2035, the Sun on this date has fallen between roughly twenty three and twenty four and a half degrees of Cancer. The spread is narrow because the leap year cycle keeps the calendar and the orbit in step, letting the position drift by about six hours a year and then snapping it back when February gains a day.
That places the Sun in the last of the sign's three faces, the stretch from twenty degrees to thirty. Cancer is water and cardinal, and the Moon rules it in every scheme, ancient and modern alike, since it was never reassigned to one of the outer planets. That stability is unusual. Most of the older rulerships acquired a modern rival once the outer planets were found, and this one did not.
The Chaldean face and its ruler
The Chaldean order runs the seven visible planets in sequence from the fastest moving to the slowest, Moon, Saturn, Jupiter, Mars, Sun, Venus, Mercury, and repeats that cycle through the thirty six faces of the zodiac starting at zero degrees of Aries. Count it out and the final face of Cancer lands back on the Moon.
So the ruler of the sign and the ruler of the band are one body. The competing triplicity scheme, which assigns each face to a sign of the same element in order, gives these degrees to Pisces and therefore to Jupiter. Both readings sit in water, which is why they are usually described as pulling in a similar direction here rather than contradicting each other.
What the tradition reads into it
Traditional writers treat a repeated ruler as an intensifier. The themes attached to the Moon, memory, tides of mood, care and its withdrawal, are read as less diluted in this band than in the earlier faces of Cancer, where Mars and then the Sun take the Chaldean turn. Under the Jupiter reading the same degrees are given a wider and more diffuse cast.
None of that is measurable and it should not be presented as if it were. What is measurable is the position. The interpretation is a convention with a long paper trail behind it, and it changes depending on which scheme an author follows, which is itself a reason to hold it loosely. Reporting a convention accurately means naming the scheme it came out of, and most sources quoting a decan ruler skip that step entirely.
The limits of a date
Two people born on the same 16 July, one at dawn in Auckland and one at dusk in Lisbon, share this solar degree to within a fraction and share almost nothing else. The Moon travels about thirteen degrees a day, so it can change sign inside that span. The ascendant moves through the whole zodiac in twenty four hours, which puts it beyond the reach of a date entirely.
The widget above is where the rest of it starts. Give it your year, your hour and the place you were born and it returns the exact solar degree instead of the noon figure, plus how far that degree sits from the nearest sign boundary. On this date the answer will be several days, which is worth confirming rather than assuming.
Questions people ask about this
Which planet rules a 16 July birthday?
The Moon rules Cancer, and in the Chaldean face order the Moon also rules the twenty to thirty degree band this date falls in. The triplicity scheme gives that band to Jupiter instead.
Is 16 July ever Leo?
No. Every year from 1930 to 2035 checked at noon puts the Sun near twenty three degrees of Cancer, with about a week of the sign still to run.
What is a decan?
A ten degree third of a sign. Every sign has three, which makes thirty six across the zodiac, and each carries a ruling planet under whichever scheme you follow.
Why do sources disagree about the ruler?
Because two systems survived side by side. The Chaldean order counts planets by speed through all thirty six faces, while the triplicity scheme assigns each face to a sign of the same element.
Does the doubled rulership make Cancer stronger?
That is how the tradition reads it, as emphasis rather than addition. It is an interpretive convention, not a measurement, and the other scheme reads the same degrees differently.
Do I still need my birth time?
For the sun sign, no. For the Moon, the rising sign and the houses, yes, since all three depend on the hour and the birthplace as well as the date.