7; 9,20 M

7; 9,20 M

7; 9,20 M

7; 9,20 M

Table 91. Excess of revolution for the Sun in a year

Nu, f. 96r: Aequacio revolucionum Rc, f. 79r: Equatio revolutionum

Ed. 1526, f. 386v: Tabula equatonis [revolutionibus] [symbol for the Sun]

As is the case for most other tables above, this table is unprecedented in the astronomical literature, as far as we know: see Table 91. The argument is the true solar longitude, given in degrees at intervals of 1°. The entries, in seconds of an hour, represent the correction, whether negative (mi.) or positive (adde), to be applied to the time given in the preceding table when the Sun returns to the same true longitude after approximately 1 year.

In the first worked example presented in Chapter 40 we are asked to consider as epoch Nov. 8, 1383 at 18;38,4h. We are told that the true position of the Sun is Sco 24;59,39° = 234;59,39°. The problem is to find the time in year 1435 when the Sun was in the same position as it was in the year of the epoch. These two dates are relatively close, for they are only separated by 52 years. In Table 88 we find the excesses for 40y (7;9,20h) and 12y (2;8,48h). Both entries are found in the column headed 3, corresponding to the third year after a leap year, which is the case for 1383 and 1435. Both entries are assigned the letter M, for minue (subtract). Subtracting the sum of these two entries (9;18,8h) from the epoch, we obtain 9;19,56h. This time has to be corrected for the specific solar position (Sco 24;59,39° = Sco 25°) whose entry in Table 91 is 0;0,26h, with the notation adde (add). We are then told to multiply this correction by the number of years elapsed, and to add the result, 0;22,32h, to the time found previously, 9;19,56h. The new result, 9;42,28h, corresponds to the time on Nov. 8, 1435 when the Sun was in the same position as in the year of the epoch.

Table 91: Equation of the excess of revolution for the Sun in a year

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