A settled noon and a moving edge
Sagittarius begins at two hundred and forty degrees of ecliptic longitude. Across the years covered here that point is reached on 21 or 22 November, usually well after midday by universal time, so the noon reading on the twenty first is Scorpio each time.
The edge itself never stays still. A tropical year exceeds the common calendar year by close to a quarter of a day, so an ingress arrives about six hours later than it did the year before, then jumps back roughly eighteen hours when February gains a leap day. Watch this crossing over a decade and it covers about a day and a half of calendar. Scorpio is also one of the shorter signs, running near twenty nine and a half days because the Sun is accelerating towards perihelion in early January, and that faster motion gives the late autumn boundaries a drift pattern slightly unlike the long summer ones.
Why the hour and the city belong in the calculation
In years where the crossing falls during the twenty first, the hour of birth decides the sign outright. A birth at breakfast and a birth at midnight on the same date can be different answers, and a default of noon hides that rather than resolving it.
Location adds the second layer. An ingress is a single global instant, so a crossing at 03:00 UTC on 22 November is ten in the evening on the twenty first in New York. The same sky, two calendar dates, and only one of them agrees with whichever range the reader consulted. That single mismatch is the most common source of an incorrect sun sign. The widget above takes the year, the hour and the birthplace and reports both the sign and the number of hours between your birth and the crossing.
The cusp is a gap in the paperwork
Being told you are a Scorpio Sagittarius cusp usually comes with a description of intensity loosened by wanderlust. Nothing in the sky answers to it. The Sun holds a single longitude at any moment, and that value falls short of two hundred and forty degrees or exceeds it. There is no width to the boundary and no interval in which both signs apply.
Read the word as a note about what was missing. It appears where a date is known and a year, an hour and a birthplace are not, and hedging across both signs is the only honest response to that. Once the record is complete the hedge has nothing to protect against.
Scorpio and Sagittarius in contrast
Scorpio is fixed water, ruled by Mars in the traditional scheme and by Pluto in the modern one, read as concentrated, guarded and unwilling to release a subject. Sagittarius is mutable fire ruled by Jupiter, read as expansive, opinionated and restless with detail. They share no element, and fixed giving way to mutable is where holding fast turns into moving on, so the two readings pull firmly apart.
If the answer is not the one you were raised with, the practical loss is small. The Sun is one placement, and the Moon, the Ascendant and every planet keep the positions they had regardless of which side of two hundred and forty degrees the Sun fell on.
Questions people ask about this
Is 21 November Scorpio or Sagittarius?
Scorpio at noon in every year from 1930 to 2035. The crossing into Sagittarius comes later that day in some years, so an evening birth is worth checking with the widget above.
Why do tables disagree about when Scorpio ends?
Because the crossing moves through about a day and a half over a decade and a printed range cannot follow it. Each publisher froze a different year, which is why the end date is given as the twenty first, second or third.
Does the hour of birth matter on this date?
In the years where the ingress falls on the twenty first itself, yes, entirely. A morning birth is Scorpio and a late evening birth in the same place can be Sagittarius.
Am I on the Scorpio Sagittarius cusp?
No, since there is no space between two signs to occupy. Your Sun had one longitude at birth and that longitude lay inside one sign. The term describes absent birth details.
Is Scorpio really shorter than a month?
Usually. The Sun is speeding up towards perihelion in early January, so it crosses Scorpio in about twenty nine and a half days rather than the thirty one that spring signs can take.
Does a Sun in the last degrees of Scorpio still count?
Fully. The sign applies to its final minute. The degree affects which aspects form and which house the Sun occupies, and it does not dilute the sign.