Mariners of the 17th, 18th and 19th Centuries knew that the shoal waters to the east and south of Sankaty Head presented a real danger because of the shifting currents, the movement of the sand bars, and the imprecise charts of the area. Ships, cargoes and lives were lost here. The need for a safe passage through this treacherous region was apparent to seamen and landlubbers alike.

In 1848 Congress appropriated $12,000 to erect a light on the high bluff, the southeasternmost headland in New England, to mark the location of these perilous waters and to identify a refuge below the bluff for ships endangered by strong westerly winds.

Sankaty Head Light rose sixty feet above the hundred-foot tall bluff and was topped by America's first Fresnel lens. This lens, a series of prisms and magnifying glasses designed by France's Augustin Fresnel, concentrated light into a narrow beam that was visible as far as twenty miles away.

Sankaty Head Light was lit for the first time on February 1, 1850 and has been in continuous service ever since. The first light was provided by a single wick whale oil lamp. At the time Sankaty's beam, focused through the Fresnel lens, was the brightest man-made light in the world.

The first Keeper of the Light, Captain Alexander Bunker and his two assistants, stood four-hour watches to fuel the lamp and wind the clockwork mechanism that rotated it. Over the years changes and improvements were made, increasing the light's height to its present 70 feet, electrifying and automating the light, and removing the Keeper's quarters.

In 1969 the Coast Guard removed the lantern and deck, replacing them with "...an odd-shaped aluminum cap." Following impassioned objections by the public, the Coast Guard rebuilt the deck and lantern and in 1970 Sankaty once again "...looked like a lighthouse."

Even with today's high tech navigational instruments and equipment, and accurate, up dated charts, the shoal waters off Sankaty Head, as in earlier times, are potentially dangerous. The busy shipping lanes continue to be protected by the venerable lighthouse, which is itself in danger as the sea continues to erode the base of the Sankaty Head bluff.

Sankaty Head's classic Fresnel lens and its clockwork mechanism are on display in Nantucket's Whaling Museum.