It’s a tough question, deciding what is common knowledge and what requires attribution (citation/reference in APA format).
Listen to the podcast at Internet Archive.
I use an example from the university’s plagiarism tutorial to demonstrate the difficulty that we (as scholars) can face. The tutorial gives an example of common knowledge facts; however, I am willing to bet that most of us aren’t able to correctly answer one of the questions posed as an example. In fact, I rarely meet folk between the age of 10 and 40 that can correctly answer the example question…
What is the mean distance between the Earth and the Sun?
I will post the answer in a moment, just in case you want to test yourself. If you were to including this data in an academic paper and you had look up the answer, you should include a citation/reference to your research source. However, the university’s tutorial explains that this is common knowledge and does not require a citation/reference. For about a year, I have been quizzing students and other adults that I meet…so far, only a couple of folk (out of many hundreds that I have asked) have known the correct answer. The correct answer is: the mean distance between the Earth and the Sun is 93 million miles.
It is incumbent on all of us to be academically honest. I confirmed my data at NASA’s Web site.