Scientists in the 19th century believed that a hidden ninth planet, Vulcan, orbited between Mercury and the Sun—until Einstein buried the theory once and for all.
Explore the fact-checked online encyclopedia from Encyclopaedia Britannica with hundreds of thousands of objective articles, biographies, videos, and images from experts.
Finding Neptune: How we discovered the eighth planet astronomy.com - get the latest breaking news, showbiz & celebrity photos, sport news & rumours, viral videos and top stories from astronomy.com Daily Mail and Mail on Sunday newspapers.