Grammatically, the phrase functions as an interrogative clause. Its primary purpose is to solicit a specific piece of information: a numerical quantity. The core of the query, "how many days," is an interrogative phrase where "how many" serves as a determiner modifying the noun "days." The entire clause is structured to elicit a noun phrase (a number) that represents the duration between a fixed start date and a variable end date.
To determine the value, two points in time must be established: a start date and an end date. The phrase implies a start date of September 11, which, due to historical context, is almost universally understood as September 11, 2001. The end date is "today," a dynamic variable that changes daily. The calculation involves computing the total number of days between these two dates. This is achieved by summing the days remaining in the start year, the total days in all the full years that have passed (accounting for 366 days in each leap year), and the number of days that have elapsed in the current year up to the present date. A more direct computational method involves converting both the start and end dates to a standardized serial date format (e.g., Julian day number) and finding the difference between the two values.
The practical application of this calculation is to produce a precise, quantitative measure of the temporal distance separating the present moment from a significant historical event. The resulting number is not static; it increments by one each day, serving as a continuously updated metric of elapsed time. This value is used in historical analysis, data journalism, and commemorative contexts to frame the passage of time, converting a general sense of duration into a specific, tangible data point that can be used for comparison and reflection.
