College professors will usually require some scholarly (also academic, peer-reviewed) sources.
Three things to look for:
Anyone can publish online, so make sure to evaluate the reliability and appropriateness of your sources. Consider all of the following when evaluating a source:
If you doubt the credibility of a source based on the above criteria, look elsewhere to confirm (or discredit) the source.
Scholarly Journals vs. Popular Magazines
Scholarly journals are often confused with popular magazines like Time, Newsweek, and U.S. News & World Report. Both are published on a regular schedule (weekly, monthly, quarterly, etc.) and both consist of short articles on a variety of topics. This chart shows clues that you can look for to determine whether an article comes from a scholarly journal or a popular magazine.