What is considered a credible source on the Internet?
There are a few categories of credible sources that you can rely on: academic sites, scientific sites, sites backed by well known entities, news sites, non-scientific sites written by experts in their fields.
Academic sites for universities and colleges (sometimes high schools as well) post research, press releases and course lecture material. Research and press releases are posted under the auspices of the institution itself therefore can be trusted as credible. If any doubt remains, each provides contact information for the research team or the writer for factual confirmation. Lecture or supplementary material can be authenticated through the professor or lecturer who wrote it. It may take some creative clicking to find the Home page or CV (resume) of the writer but it can be done.
For example, this URL leads to a page of information on Edmund Spenser's Amoretti:
It doesn't look elegant compared to some Web pages, so you may want to verify credibility. There is no "by" line nor is there a notation at the bottom of the page identifying the author. There is also no About page link. But there are clues to follow. At the bottom of the page is a link to the course syllabus. At the bottom of that page is a link to the course Home page. On the Home page, the author identifies himself as Arnie Sanders, Department of English of Goucher College, and provides a link to his CV, which identifies him as "Arnold Sanders, Associate Professor of English." Another small link takes us to his actual CV where we learn he took his Ph.D. from Brown University in 1968. The Spenser Amoretti page has been authenticated as credible.
Another route to authentication of this site is to read the URL and search for goucher.edu: www.goucher.edu . That takes you to the college Home page where you can click Faculty And Staff, then select "Faculty & Staff," choose "S" and find Sanders' name in the Faculty Directory. This directory listing does not link to his CV but does authenticate his qualifications and provide credibility to his site pages.
Scientific sites are easier to identify and verify. They will often be identified with a university or government. Here are three examples you can look up: Mullard Space and Science Laboratory, The Marshall Space Flight Center, British Antarctic Survey.
historyextra.com is an example of a site backed by a known entity. Look it up and you'll see it is associated with the BBC and Immediate Media. You can find this information at the bottom of the page or under About Us. News sites are similar. You can know that Barrons, The Wall Street Journal, The New York Times, etc are credible, and they often have much more than news, as does the BBC News site. Popular sites like LiveScience.com list their sources so you can often verify their information from the original source. New websites, like moneycrashers.com, can be authenticated by the founders and writers.
Other sites written by experts can also be authenticated as credible by tracking down founders and authors. victorianweb.org is one of these. Like Sanders pages, it doesn't look impressive, yet you fill find it is associated with the Nagoya University of Japan (bottom of Entry page). Under "What is the Victorian Web?" you will find pertinent information about contributors and that it was founded by George P. Landow Ph.D. Web search his name and you find he took his Ph.D. from Princeton. Articles also carry "by" lines with academic affiliation. This ought to get you going in the right direction.