Sadly, I have never spoken to a blind person asking them what they understand the Sun, a Star, a Black Hole, a Galaxy of Stars(?),... to be... somehow I hold though, that if blind people were to have more of a say in this world, there might be some disagreement as to what the Sun exactly is... I am yet to see a blind astrophysicist. Try to put yourself in their shoes... ?Known by whom? The quoted statement appears redundant. I think a more contextual statement would be: "What can be known by humanity is limited to what we can directly or indirectly perceive."Science is as intellectual as it is empirical. Not every result of an experiment can be repeated by every scientist; some experiments are just too complex/difficult/expensive.