Where the Sun actually stands on 13 April
Taken at noon in every year from 1930 to 2035, the Sun on this date has stood between roughly twenty two and a half and twenty four degrees of Aries. The spread across more than a century is under a degree and a half, which is far narrower than most people expect.
The reason is the leap year cycle. A tropical year runs about a quarter of a day longer than a calendar of three hundred and sixty five days, so the Sun arrives a little later each year, and then the extra February day pulls it back. The two effects cancel over four years, and the date keeps returning to almost the same longitude.
Twenty to thirty degrees, and who rules it
Each sign divides into three faces of ten degrees. Twenty three degrees falls in the last of the three in Aries, the stretch from twenty up to the Taurus boundary at thirty.
The Chaldean order runs Mars, Sun, Venus, Mercury, Moon, Saturn and Jupiter in an unbroken loop from the start of Aries, and counting forward it hands this face to Venus. The triplicity scheme ignores that loop and gives each decan of a sign to a sign of the same element in turn, so the fire decans go to Aries, Leo and Sagittarius, and the last one lands on Jupiter. Neither count is a corruption of the other. They were built on different principles and they were both in use.
What the tradition reads into each answer
Under Venus the reading softens a Mars sign. The older material treats the pairing as heat with something sociable attached to it, Aries drive turned outward rather than inward. Under Jupiter the reading widens instead, and the face is described in terms of scope and conviction rather than charm.
Both of those are interpretation and should be marked as such. The checkable part is the position: a Sun in the closing third of a cardinal fire sign whose domicile ruler is Mars in either scheme. What a reader does with the face ruler depends on which tradition they have decided to follow, and it is worth knowing that a source quoting one of them has usually not told you it made that choice.
The parts a date cannot reach
The Sun is one body. On 13 April the Moon can be in either of two signs depending on the hour, since it covers roughly thirteen degrees a day and changes sign every two and a bit days. The rising sign is worse still for a date alone, because the whole zodiac passes the horizon in a day and any of the twelve can be there.
That is why the sun sign is the least personal part of a chart rather than the most. It is shared with everyone born within about a month of you in any year. The widget above takes your year, hour and birthplace, returns the exact degree instead of the range on this page, and reports how far the birth fell from the nearest sign boundary.
None of the layers above is a claim about the reader either. A face ruler describes a stretch of the zodiac in the terms of an old system, and that is a different kind of statement from saying a date makes a person one way or another. The site keeps those apart deliberately, because the first can be checked against the scheme it comes from and the second cannot be checked against anything.
Questions people ask about this
Is 13 April always Aries?
Yes. Checked at noon in every year from 1930 to 2035, this date fell in Aries each time, with several days of margin before the change into Taurus. No year in that sample comes close to the boundary.
What degree of Aries is a 13 April birthday?
Near twenty three degrees, within a band of about twenty two and a half to twenty four across the last century. The widget above will give the exact figure once it has your year, hour and birthplace.
Which decan does this date fall in?
The third decan of Aries, the stretch from twenty to thirty degrees. Every year in the sample sits inside it, so the date settles the decan as firmly as it settles the sign.
So is the ruler Venus or Jupiter?
It depends on the scheme. The Chaldean face order gives Venus, the triplicity scheme gives Jupiter. Most modern sources quote one without saying which, and that is where the confusion starts.
Does the decan change my sun sign?
No. The decan is a subdivision inside the sign, not an alternative to it. A Sun at twenty three degrees of Aries is fully Aries whichever planet you assign to the face.
Does my birth time matter for this date?
Not for the sun sign, which is settled either way. It matters for everything else, including the Moon, the rising sign and the house positions, none of which a calendar date can supply.