They realized this as result of the number of sunspots getting larger and smaller over the course of the years .
What is Sunspot?
This is defined as a temporary phenomena on the Sun's photosphere that appear as spots darker than the surrounding areas.
The presence of these sunspots is what gave Astronomers the idea of the Sun having varying levels of activities over the years.
Read more about Sunspots here https://brainly.com/question/4953210
