Sunspots  delta_S   time
S     dS        t

58  4.6 1
62.6    4.6 2
70  4.6 3
55.7    7.4 4
85  -14.3   5
83.5    29.3    6
81.6    -1.5    7
...
...
50.6    6.9 3153
78  6.7 3154
88  27.4    3155
96.7    10  3156
73  8.7 3157

D(S) = f(S)

F2 =AVERAGE(OFFSET($C2;-CELL("contents";F$1)+1;0;CELL("contents";F$1);1))
and propagate to all rows ...