This means that Eratosthenes estimated the circumference of the Earth to be about 40,000 km. He also knew that the circumference of a circle was equal to 2 times Ï (3.1415...) times the radius of the circle. (C = 2Ïr) With this information, Eratosthenes inferred that the Earth's radius was 6366 km.
Ankylosing spondylitis is a form of chronic inflammation of the spine and the sacroiliac joints. The sacroiliac joints are located at the base of the low back where the sacrum (the bone directly above the tailbone) meets the iliac bones (bones on either side of the upper buttocks) of the pelvis.
Doctors know a lot about how ankylosing spondylitis develops and leads to symptoms, but are still trying to understand what causes the disease. The symptoms of ankylosing spondylitis are caused by inflammation of parts of the lower spine. This inflammation can lead to damage and fusion - through the growth of new bone.