Answer to Question 1
The escape velocity of a celestial object is the speed that an object on its surface needs to escape the gravitational field. A black hole is so dense that the escape velocity is greater than the speed of light, so light cannot escape the black hole; hence, the term black.
Answer to Question 2
It became known as the Copernican Revolution because it was not just the adoption of a new idea but a total change in the way astronomers, and, in fact, all of humanity, thought about Earth and its place in the Universe. In fact, our modern use of the words revolution and revolutionary to describe philosophical, political, and social upheavals comes from the title of Copernicus's book, De Revolutionibus, which means On Revolutions.
Black Knapweed
In this painting evangelist George Whitefield appears to be cross-eyed. This is no fault of John Wol
The Ku Klux Klan forces John Campbell, a black man, to beg for his life in Moore County, North Carol
Clay Lohmann, Black Lung.
Black-tailed Prairie Dog (Cynomys ludovicianus).