The position first
Taken at noon across 1930 to 2035, the Sun on 7 April has sat between roughly sixteen and three quarters and eighteen degrees of Aries. Every year in that sample lands in the middle band of the sign, well clear of both edges.
The stability comes from the leap year cycle. Each ordinary year the Sun is about a quarter of a degree further along on a given date, and each leap day pulls it back by close to the amount three ordinary years added, so the position oscillates within a narrow band instead of drifting.
Two schemes for the same ten degrees
The Chaldean scheme runs the seven visible planets in order of apparent speed, from Saturn down to the Moon, and lays that sequence continuously across the zodiac from the first degree of Aries. Counting through, the middle band of Aries falls to the Sun.
The triplicity scheme works differently. It gives the first band of a sign to the ruler of that sign, then the second and third to the rulers of the other signs of the same element, in zodiacal order. Aries, Leo and Sagittarius are the fire signs, so the bands of Aries go to Mars, then the Sun, then Jupiter. The middle band again falls to the Sun.
What agreement is worth
Where the two schemes agree, a reader can at least be confident they are looking at a settled convention rather than a choice between traditions. That is not the same as evidence. It means the sources are consistent, not that the assignment describes anything measurable.
Elsewhere in the zodiac the schemes part company. The last band of Aries goes to Venus in the Chaldean order and to Jupiter by triplicity, which is why a reader born a fortnight later can find two confident and contradictory answers online. Knowing that the disagreement is structural saves a good deal of confusion.
Neither scheme claims to be a measurement, and neither set of sources argues the point at any length. They are systems of assignment, and the tradition uses them to narrow a description rather than to establish a fact.
What the schemes leave untouched
Neither system says anything about the Moon, which crosses about half a sign a day and can change sign during 7 April. Neither says anything about the rising sign, which turns through the full zodiac every twenty four hours and depends on the latitude of the birthplace as well as the clock.
Both are layers of description sitting on top of a single solar position. The widget above gives that position exactly for a chosen year and place, and adds the placements a date on its own cannot supply, including how far the birth fell from the nearest sign boundary.
Aries itself is cardinal fire under Mars, read as direct and quick to start. The band narrows that description; the rest of the chart is where two people born on the same date actually differ.
Questions people ask about this
Who rules the decan for a 7 April birthday?
The Sun, in both of the schemes usually quoted. The Chaldean order arrives there by planetary speed and the triplicity scheme by the rulers of the fire signs, and for this band the two routes coincide.
What degree is the Sun on this date?
About seventeen degrees of Aries, within a window of roughly a degree and a quarter across the last century. Your year fixes which end of the window applies.
Why do sources disagree about decan rulers elsewhere?
Because there is more than one scheme, and they were built on different principles. One follows planetary speed and the other follows the element of the sign, so they coincide on some bands and not on others.
Is 7 April ever a sign other than Aries?
No. It falls roughly halfway through Aries season, with about a fortnight of margin to each boundary, so no year or hour of birth changes the sign.
Does a decan ruler change my sun sign reading?
It refines it rather than replacing it. The tradition treats the sign as the main statement and the band as a qualification on the description.
Can I check this position myself?
Yes. Any ephemeris for your birth year gives the solar longitude for the date, and the widget above computes it directly from a year, a time and a birthplace.