The certainty, and its size
On 16 December the Sun stands near twenty four degrees of Sagittarius. Across every year from 1930 to 2035, measured at noon, the figure runs from about twenty three and a half to twenty five, which keeps it firmly inside the third face of the sign.
The face is the band from twenty to thirty degrees. Saturn rules it in the Chaldean order, Leo in the triplicity scheme, and Jupiter rules the sign itself throughout. That much can be stated for anybody born on this date without asking a single further question.
It is also, in chart terms, a modest amount of information. The Sun is shared with everyone born across four weeks and the face with everyone born across ten days. Neither figure narrows a person down in the way most readers assume a birthday does.
The degree is worth having all the same, because it decides which transits contact the Sun and by what margin. That is a working detail rather than a character claim, and it is one of the few things about a birthday that can be checked against an ephemeris.
The Moon has more than one answer
The Moon crosses roughly half a sign in a day, which means a boundary can fall at any hour and often does. On this date the lunar sign has at least two candidates in most years, and where the crossing happens near the middle of the day the split is close to even.
Since the Moon is read as need, habit and reaction rather than intention, the difference between the two candidates is not a technicality. It is the placement most people find most recognisable once they have it.
A date alone cannot supply it. A birth time and a chart calculation can, and where the time is unknown a calculation will at least say whether the Moon held one sign all day.
The horizon is wide open
The rising sign has no connection to the date whatsoever. The full zodiac passes the eastern horizon in twenty four hours, so any of the twelve can rise on 16 December, and it changes every couple of hours as the earth turns.
Place matters as much as time. Two births at the same instant in different longitudes have different Ascendants, because the horizon is a local thing rather than a global one. That is why a birthplace is asked for alongside an hour.
The houses are measured from the Ascendant, so an unknown time leaves the whole house layer undetermined. The planets sit in the same signs either way, and which department of life they are read into is unsettled.
Why the sun sign dominates anyway
The reason is practical rather than technical. A date is the one piece of birth information everybody knows and nobody has to look up, so it became the basis of the material that reaches most people.
That is a fact about publishing rather than about astrology. In the older texts the Ascendant and the Moon carry at least as much weight, and the Sun is one factor among several rather than the headline.
The widget above returns your exact solar degree from your year, hour and birthplace, along with the distance to the nearest sign boundary. For the Moon, the Ascendant and the houses, a full chart is the only honest route.
Questions people ask about this
What sign is 16 December?
Sagittarius, with no boundary question. The Sun does not leave the sign until around 21 December, so the date is settled in every year on record.
What is my Moon sign for this date?
The date cannot tell you. The Moon may cross a sign boundary at any hour, so most 16 December births have two possible lunar signs until a time is supplied.
Can the rising sign be worked out without a birth time?
Not properly. All twelve signs rise during a day, so the Ascendant depends on the hour and the birthplace rather than on the date at all.
What degree and decan is the Sun on?
Near twenty four degrees of Sagittarius, inside the third decan. Saturn rules that band in the Chaldean order and Leo in the triplicity scheme.
Why is the sun sign the one everybody quotes?
Because a date is the only birth detail everyone remembers. It is a convenience of publishing rather than a judgement about which placement matters most.
Is a chart worth calculating if my birth time is unknown?
Usually yes. The signs of the planets, the Sun to the degree and most aspects can still be worked out, and the parts that cannot are then clearly marked as unknown.