How can sun - pots help to determine the period of rotation of the sun?
Because sun spots appear to move across the surface due to the
sun's rotation. Observe the sun by projecting its image onto a
piece of paper through binoculars or a small telescope.
(Never look directly at the sun of course with or without
binoculars or telescope unless you want to immediately go
permanently blind!) Observe over a few weeks day by day and note
the time when a sun spot just appears at the edge of the sun. Track
this spot day by day and note the day when it reaches the other
side and disappears. It will therefore have appeared to travel over
half the sun's surface (the half we can see) because of the sun's
rotation. If you double this figure (to take into account the
apparent journey across the surface of the sun that we cannot see)
then this figure will be the time for the sun's rotation.