People have practiced the science of astronomy since ancient times and the discipline has no formal inventor. Knowledge of astronomy stretches back prior to recorded history, as evidenced by such ruins as henge circles, sky disks, moon calendars and sun dials.
Some of the earliest recorded astronomers include the Greeks Eratosthenes and Claudius Ptolemy, the Persian Abd al-Rahman al-Sufi and the Indian Aryabhata. In modern times, astronomers credited with notable discoveries and inventions include Nicolaus Copernicus, Tycho Brahe, Johannes Kepler, Galileo Galilei, Christiaan Huygens and Isaac Newton. Prominent 20th-century astronomers include Albert Einstein, Edwin Hubble, Carl Sagan and Stephen Hawking.