Derby Wharf Light Station is a historic lighthouse

Lighthouse

A lighthouse is a tower, building, or other type of structure designed to emit light from a system of lamps and lenses or, in older times, from a fire, and used as an aid to navigation for maritime pilots at sea or on inland waterways....

 on Derby Wharf in Salem, Massachusetts

Salem, Massachusetts

Salem is a city in Essex County, Massachusetts, United States. The population was 40,407 at the 2000 census. It and Lawrence are the county seats of Essex County...

 that is within the Salem Maritime National Historic Site

Salem Maritime National Historic Site

The Salem Maritime National Historic Site consists of 12 historic structures and about 9 acres of land along the waterfront in Salem, Massachusetts, plus a Visitor Center in downtown Salem...

.

It was built in 1871 and added to the National Register of Historic Places

National Register of Historic Places

The National Register of Historic Places is the United States government's official list of districts, sites, buildings, structures, and objects deemed worthy of preservation...

 in 1987. The United States Coast Guard Light List

Light List

The United States Coast Guard Light List is an American navigation publication in 7 volumes made available yearly by the U.S. Coast Guard which gives information on lighted navigation aids, unlighted buoys, radiobeacons, radio direction finder calibration stations, daybeacons, racons, and LORAN...

 description is "White square tower. Maintained by the U.S. Park Service". The actual light is 25 feet (8 m) above Mean High Water

Tide

Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....

. Its red light is visible for 4 nautical miles (7.4 km).