Located on a hill in Greenwich Park, overlooking the River Thames, lies the Royal Observatory. Commissioned in 1675 by King Charles II, this is one of the world's most important scientific sites where one can learn how time was standardized and how great scientists first mapped the seas and the stars. See the UK's largest refracting telescope and touch a 4.5 billion years old asteroid. This observatory is both entertaining and educational, and has played a major role in the history of astronomy and navigation. Some prominent exhibits include John Harrison's sea watch, the H4 and the mid-20th-century Russian F.M. Fedchenko clock which is the most precise version ever made in multiple copies. Do not miss out on a star show at the Peter Harrison Planetarium, which offers a total of 120 seats and boasts extraordinary architecture that ingeniously reflects its astrological position.