Google has launched Knol, its user-generated online encyclopedia, which it announced in December but had kept under wraps in private testing.

Although its goal and approach are similar to Wikipedia's -- to tap the collective knowledge of Internet users within an encyclopedia format -- Knol is different in several ways.

Knol will encourage writers to use their real names and stand behind their articles, and will give them the possibility to generate income from their work via Google ads.

"Every knol will have an author, or group of authors, who put their name behind their content. It's their knol, their voice, their opinion. We expect that there will be multiple knols on the same subject, and we think that is good," wrote Knol product manager Cedric Dupont and software engineer Michael McNally in an official blog posting Wednesday.

Wikipedia, on the other hand, has a culture of anonymity in which contributors rarely use their real names, and no ads appear on the site.

In addition, Knol apparently will have more controls over submissions and edits than Wikipedia. In Knol, readers can suggest changes to articles, and the authors have the final word on whether to accept or reject the feedback. "This allows authors to accept suggestions from everyone in the world while remaining in control of their content. After all, their name is associated with it," the Google officials wrote. Readers will also be able to rate articles and write reviews of them.

In Wikipedia, anyone can make changes to articles and have them appear instantly online.

Although in the blog posting knols are described as "authoritative articles about specific topics, written by people who know about those subjects," a Google spokesman said that anyone can write an article.

"Google will have no advance knowledge of the content of a knol and we will not be doing editorial screening of content posted by users and authors," he wrote via e-mail.

In addition, Google will encourage authors to use their real names, but will not require it, he said. Google will give authors the ability to have their identity confirmed via a telephone or credit card verification process. Articles penned by these authors will appear with a "verified" stamp, he said.

Another difference is that in Wikipedia all content is licensed under the GNU Free Documentation License. This means that Wikipedia content can be copied, modified, and redistributed, as long as the new version extends those same freedoms to others and acknowledges the authors of the Wikipedia article used.

In Knol, authors will get two options for licensing their work. They may choose to reserve some rights using a Creative Commons license. They also may opt for a traditional copyright license format to reserve all rights.