Galileo's Starring Messenger

The telescope and the microscope were both invented within a decade of each other in the early 1600s. The Dutch had perfected optics long before anybody else did, so it's not a surprise that those two inventions came out of the Netherlands. With the telescope, Galileo sees that Venus has phases like the moon. He sees that Jupiter has what he calls Jovian stars. Why would you think looking at the sky with this piece of equipment would bring you any different information than your eyes would? Same with a microscope. Why aren't your eyes just seeing everything that's seeable?