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.
Bay (left) and chestnut (sometimes called "sorrel") are two of the most common coat colors
Black and Tan Coonhound
Cataract extraction. The procedure involves a surgical removal of a cataract lens and its replacemen
The effective temperature, or black body temperature, of the Sun (5777 K) is the temperature a black
black-eyed susan (2)
Structure of a Schwarzschild (Nonrotating) Black Hole