Why must astronomers say that the sun rotates once evert 27 to 31 days?

Answer 1

Since the sun isn't solid, there's no reason that all of it has to rotate at the same rate,

and in fact it doesn't. Different "latitudes" on the sun rotate at different Why_do_astronomers_say_that_the_sun_rotates_once_every_27_to_31_days_rather_than_give_an_exact_number. One belt

rotates every 27 days, another belt rotates every 31 days, and there are other belts

in between those that rotate at every rate in between 27 and 31 days. So there isn't

a single "exact number" for the sun, as there is for every solid body including the earth.

For any rate you want to name between 27 and 31 days, there's a part of the sun that

rotates exactly once in that period of time

Answer 2

Astronomers say that the Sun rotates once every 27 to 31 days because different parts of the Sun rotate at different speeds due to its gaseous nature. This differential rotation creates the range of rotation periods observed by astronomers.