Linda Goodman's Sun Signs
Sun signs were mass reading before Goodman: the New York Post printed forecasts for each sun sign from 1936, after London's Sunday Express began a column in 1930.
Geoffrey Dean and Arthur Mather, 'Sun Sign Columns: History, validity, and an armchair invitation', expanded from Astrological Journal 38(3), 1996 (astrology-and-science.com)
Linda Goodman's 1968 book on the twelve sun signs, published by Taplinger in New York.
More context
Linda Goodman's Sun Signs was published by Taplinger in New York in 1968, as the original edition record confirms. Pan Macmillan's later edition describes twelve sign portraits applied to men, women, children, bosses and employees. That is the book's astrological reading of character and relationships. Its commercial publication did not begin newspaper astrology. Dean and Mather trace a London Sunday Express column to August 1930 and forecasts for each sign in the New York Post to 1936. Those earlier newspaper dates distinguish the history of the format from the success of Goodman's book.
Light
Pan Macmillan presents Goodman's sign portraits as a way to understand the people in one's life.
Shadow
Goodman's own caveat, quoted by Pan Macmillan, denies that every person fits a sign's stereotype.