A 17th-century brass astrolabe, said to be the "perhaps the largest in existence" by Sotheby's Benedict Carter, is up for auction in London on Wednesday. The BBC reports that it's 30cm wide and 46cm tall, and weighs 8.2kg. ending up in the royal collection of Jaipur's Maharaja Sawai Man Singh II , but originally commissioned by Aqa Azfal, a nobleman in Lahore. The astrolabe, an ancient navigational computer, has 94 cities inscribed on it, marked according to their longitude and latitude, and maps them by 38 stars, indicated by "intricate floral tracery." The mechanism features five plates. This particular instrument was made in the early 17th Century in Lahore, now in Pakistan, at a time when the city had become a leading hub of astrolabe-making in the Mughal world. It was created by two brothers, Qa'im Muhammad and Muhammad Muqim, for a Mughal nobleman. The pair were part of the so-called "Lahore School", one of the most renowned centres of astrolabe production of its time.…