What the date does settle
At noon in every year from 1930 to 2035 the Sun on 15 April stood between roughly twenty four and a half and twenty six degrees of Aries. That is the sign, with no doubt attached, and the degree to within about a degree and a half.
It also settles the face. Twenty five degrees sits in the last of the three ten degree bands in Aries, the stretch from twenty to thirty, given to Venus in the Chaldean order and to Jupiter in the triplicity scheme. Sign, degree and face, all from a date. That is more than most sources offer and it is where the date's usefulness ends.
The Moon, which the hour decides
The Moon moves about thirteen degrees a day and changes sign every two and a bit days. On any given 15 April it will be in one sign for part of the day and, quite often, in the next one by the evening. Across different years it can be in any of the twelve.
That matters because the Moon is not a minor placement. In both traditional and modern practice it carries the material about temperament and habit that people usually go looking for under their sun sign. A date alone cannot produce it. A date with an hour and a place can.
Worth adding that the sign is settled at any hour on this date, not merely at noon. The Taurus boundary is several days ahead and the year to year drift in it runs to about a day and a half, so no combination of birth hour and time zone brings it within reach. That is a stronger statement than a date range can make, because a range is itself an approximation of a moving instant.
The rising sign, which the place decides too
The ascendant is the degree of the zodiac coming over the eastern horizon at the moment of birth. The whole circle passes in a day, so it moves through a sign roughly every two hours and through all twelve between one midnight and the next.
Latitude changes how long each sign takes, so two births at the same clock time in different countries can have different ascendants. This is why an unknown birth time is a real limitation rather than a technicality, and why the houses, which are laid out from the ascendant, go with it.
Reading the sun sign at its proper weight
Everyone born within about a month of you in any year of history shares your sun sign. Roughly one person in twelve has it. That is a useful thing to know and a poor description of an individual, and treating it as the headline is what makes so much birthday writing interchangeable.
The honest version is narrower and more interesting. The date gives a Sun in the closing third of a cardinal fire sign ruled by Mars, at about twenty five degrees. Everything else needs your year, your hour and your birthplace, which is what the widget above asks for before it returns your exact degree and your distance from the nearest sign boundary.
Questions people ask about this
Is a 15 April birthday always Aries?
Yes. Every year from 1930 to 2035 checked at noon puts the Sun in Aries on this date, several days short of the Taurus boundary. The hour makes no difference to that answer.
What does the date not tell me?
The Moon sign, the rising sign, the house positions and every planet other than the Sun. Those need the hour and the birthplace as well as the date.
Why does my birth time matter if my sign is settled?
Because the sign is one placement. The Moon can change sign within a single day and the ascendant changes roughly every two hours, so the hour decides both.
Can I do anything without a birth time?
Yes, up to a point. The Sun, and usually the slower planets, can be placed from the date alone. The Moon may be narrowed to two candidates and the ascendant cannot be found at all.
Which decan does 15 April fall in?
The third decan of Aries, from twenty to thirty degrees. Its ruler is Venus in the Chaldean face order and Jupiter in the triplicity scheme.
Is a sun sign meaningless then?
No, just narrow. It is a real position that the tradition reads in a specific way. The objection is to treating it as a full description when it is one factor among many.