The speed of light in a vacuum, denoted by the symbol 'c,' is approximately 299,792 kilometers per second (or about 186,282 miles per second). It represents the maximum speed at which information or signals can travel through space according to the theory of relativity. The speed of light is crucial in astronomy because it determines the timescales and distances over which events occur in the universe. It allows astronomers to measure cosmic distances, calculate the age of the universe, and understand the vastness and dynamics of the cosmos. The finite speed of light also means that when we observe distant objects in space, we are seeing them as they existed in the past, providing a window into the history of the universe.