1. A computer-implemented method for determining topical authority, comprising: receiving, at a computer system, topic information for a document, the information including at least one topic and a weight for each topic, where the topic relates to content of the document, and the weight represents how strongly the topic is associated with the document; receiving authorship information for the document, the information including, for each topic in the document, at least one author and an authorship percentage for each author; generating a first update to an authority signature value for a first author of a first topic based on a product of the authorship percentage for the first author of the first topic and the weight of the first topic in the document, where the first topic is included in the received topic information; receiving topic information for a second document, the information including at least one topic and a weight for each topic; receiving authorship information for the second document, the information including, for each topic in the second document, at least one author and an authorship percentage for each author; and generating a second update to the authority signature value for the first author of the first topic based on a product of the second document first topic authorship percentage for the first author and the weight of the first topic in the second document.