Banneker's knowledge of astronomy helped him author a commercially successful series of almanacs. He corresponded with Thomas Jefferson, drafter of the United States Declaration of Independence, on the topics of slavery and racial equality. Abolitionists and advocates of racial equality promoted and praised his works.
Parks, schools, streets and other tributes have commemorated Banneker throughout the years since he lived. However, many accounts of his life exaggerate or falsely attribute his works.
Benjamin Banneker was born November 9, 1731, in Baltimore County, Maryland to his mother Mary, a free black, and his father George, a fugitive slave. There are two conflicting accounts of Banneker's family history. Banneker described himself as having only African ancestry. None of Banneker's surviving papers describe a white ancestor or identify the name of his grandmother. However, some biographers contend that Banneker's mother was the child of Molly Welsh, a white indentured servant, and an African slave named Banneka. The first published description of Molly Welsh was based on interviews with her descendents that took place after 1836, long after the deaths of both Molly and Benjamin.
Molly may have purchased Banneka to help establish a farm located near what eventually became Ellicott's Mills, Maryland, west of Baltimore. One biographer has suggested that Banneka may have been a member of the Dogon tribe that were reported to have knowledge of astronomy. Molly supposedly freed and married Banneka, who may have shared his knowledge of astronomy with her. Although born after Banneka's death, Benjamin may have acquired some knowledge of astronomy from Molly.
As a young teenager, Banneker met and befriended Peter Heinrichs, a Quaker who established a school near the Banneker family farm. Quakers were leaders in the anti-slavery movement and advocates of racial equality. Heinrichs shared his personal library and provided Banneker with his only classroom instruction. Once he was old enough to help on his parents' farm, Benjamin's formal education ended. Banneker spent most of the rest of his life at the 100 acres 0.40 km2 farm and was named on the deed in 1737.
In 1753 at the age of 22, Banneker completed a wooden clock that struck on the hour. He appears to have modeled his clock from a borrowed pocket watch by carving each piece to scale. The clock continued to work until Banneker's death.
After his father died in 1759, Banneker lived with his mother and sisters. In 1771, the Ellicott family moved to the area and built mills along the Patapsco River. Banneker supplied their workers with food and studied the mills. The Ellicotts were Quakers and shared the same views on racial equality as did many of their faith. George Ellicott lent Benjamin Banneker books and equipment to begin a more formal study of astronomy in 1788. The following year, Banneker sent George his work calculating a solar eclipse.
In February 1791, Major Andrew Ellicott, a member of the same family, hired Banneker to assist in the initial survey of the boundaries of the new federal district, which the 1790 federal Residence Act and later legislation authorized. Formed from land along the Potomac River that the states of Maryland and Virginia ceded to the federal government of the United States in accordance with the Residence Act, the territory that became the original District of Columbia was a square measuring 10 miles (16 km) on each side, totaling 100 square miles (260 km2). Ellicott's team placed boundary stones at every mile point along the borders of the new capital territory.
Banneker's duties on the survey consisted primarily of making astronomical observations at Jones Point in Alexandria, Virginia, to ascertain the location of the starting point for the survey. He also maintained a clock that he used to relate points on the ground to the positions of stars at specific times. However, at age 59, Banneker left the boundary survey in April 1791 due to illness and difficulties completing the survey. He returned to his home at Ellicott's Mills to work on an ephemeris. Andrew Ellicott continued the survey with his brothers Benjamin and Joseph Ellicott and other assistants through 1791 and 1792.
The title page of an edition of Banneker's 1792 Pennsylvania, Delaware, Maryland and Virginia Almanack and Ephemeris stated that the publication contained:
the Motions of the Sun and Moon, the True Places and Aspects of the Planets, the Rising and Setting of the Sun, Place and Age of the Moon, &c.—The Lunations, Conjunctions, Eclipses, Judgment of the Weather, Festivals, and other remarkable Days; Days for holding the Supreme and Circuit Courts of the United States, as also the useful Courts in Pennsylvania, Delaware, Maryland, and Virginia. Also—several useful Tables, and valuable Receipts.—Various Selections from the Commonplace–Book of the Kentucky Philosopher, an American Sage; with interesting and entertaining Essays, in Prose and Verse—the whole comprising a greater, more pleasing, and useful Variety than any Work of the Kind and Price in North America.In addition to the information that its title page described, the almanac contained a tide table for the Chesapeake Bay region. That edition and others listed times for high water or high tide at Cape Charles and Point Lookout, Virginia and Annapolis and Baltimore, Maryland.
The almanacs' editors prefaced the publications with adulatory references to Banneker and his race. The 1792 and 1793 almanacs contained lengthy commendations that James McHenry, a signer of the United States Constitution and self-described friend of Banneker, had written in 1791. A 1796 edition stated: