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.
Ankylosing spondylitis primarily affects the spine or back. In a person with ankylosing spondylitis, the joints and ligaments that normally permit the spine to move become inflamed and stiff. The bones of the spine may grow together, causing the spine to become rigid and inflexible.