[alphaBetaGamma]

Galileo refers in this to a book he had published earlier, the "Starry Messenger". It is well worth reading.

Galileo had just build the first ever telescope and he describes what he has discovered: there are incredibly more stars than can be seen by the naked eye; Jupiter has satellites; there are mountains on the moon and he has figured out their height from the length of their shadows... The book is full of the quiet excitement of a man who has discovered a new world, and seen what no man had seen before.

https://archive.org/details/siderealmessenge80gali/page/6/mo...

[griffzhowl]

I don't think Galileo was quite the first to make a telescope. He had heard a description of one by someone in the Netherlands, and then designed and built his own. He was the first to use it to observe and describe those otherwise invisible objects in the night sky though

[alphaBetaGamma]

If I remember correctly, in that book Galileo says he heard of someone in the Netherlands having made a microscope, but without any details about how it was made. Armed with the knowledge that something like that was possible, he designs a telescope (lenses only, not a Newton type telescope with a mirror). He build three and used the last and best to do his observations.