Via astronomical measurements.
360 days
Straddling a non-leap year, and including the start and end dates in the calculation, there are 288 days between the two dates. Straddling a leap year, and including the start and end dates in the calculation, there are 289 days between the two dates.
In a normal year, including the start and end dates in the calculation, there are 48 days between the two dates. In a leap year, including the start and end dates in the calculation, there are 49 days between the two dates.
In a non-leap year, including the start and end dates in the calculation, there are 104 days between the two dates. In a leap year, including the start and end dates in the calculation, there are 105 days between the two dates.
In a non-leap year, including the start and end dates in the calculation, there are 166 days between the two dates. In a leap year, including the start and end dates in the calculation, there are 167 days between the two dates.
Including the start and end dates in the calculation, in a non-leap year, there are 42 days between the two dates. Including the start and end dates in the calculation, in a leap year, there are 43 days between the two dates.
In a non-leap year, including the start and end dates in the calculation, there are 35 days between the two dates. In a leap year, including the start and end dates in the calculation, there are 36 days between the two dates.
In a non-leap year, including the start and end dates in the calculation, there are 64 days between the two dates. In a leap year, including the start and end dates in the calculation, there are 65 days between the two dates.
In a non-leap year, including the start and end dates in the calculation, there are 91 days between the two dates. In a leap year, including the start and end dates in the calculation, there are 92 days between the two dates.
In a non-leap year, including the start and end dates in the calculation, there are 83 days between the two dates. In a leap year, including the start and end dates in the calculation, there are 84 days between the two dates.
In a non-leap year, including the start and end dates in the calculation, there are 110 days between the two dates. In a leap year, including the start and end dates in the calculation, there are 111 days between the two dates.
In a non-leap year, including the start and end dates in the calculation, there are 96 days between the two dates. In a leap year, including the start and end dates in the calculation, there are 97 days between the two dates.