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The Chatham Lighthouse in Chatham, Massachusetts on Cape Cod, October, 2015. Chatham Light is a white conical cast-iron metal structure with a brick interior. It was erected in 1877 as one of two sister lighthouses that originally stood at the site. Its sister tower was moved to Eastham in 1923 to replace the Three Sisters lights and is now known as Nauset Light. The Fresnel lens, which was electrified in 1939, was replaced by rotating aerobeacons in 1969. The lighthouse is still under the authority of the United States Coast Guard. Tours of the lighthouse are run by the Coast Guard Auxiliary.