Final answer:
Observations of Jupiter's Great Red Spot can be used to estimate Jupiter's rotation period, which has been determined to be 9 hours and 56 minutes based on the rotation rate of cloud patterns and measurements of radio waves influenced by Jupiter's magnetic field.
Step-by-step explanation:
When astronomers observe a reddish spot on the surface of Jupiter, such as the Great Red Spot, it provides an opportunity to estimate certain characteristics of the planet. In particular, these observations can lead to an estimation of the period of Jupiter's rotation. The rotation rate can be determined by tracking the motions of distinct cloud patterns, including those associated with the Great Red Spot, which has a counterclockwise rotation period of six days.
Furthermore, more fundamental measurements of Jupiter's rotation can be made by studying periodic variations in radio waves, which are influenced by Jupiter's magnetic field. These measurements show that Jupiter has the shortest "day" of any planet, with a rotation period of just 9 hours and 56 minutes.