So, how are journal and magazine articles different?

  vs

The term "periodicals" refers to both journal and magazine articles.  There is a clear difference, however, between the two.

Can you tell by simply looking at the cover of these two periodicals?

Journal articles are scholarly and academic. Many are written by professional scholars in a particular field and can use a highly specialized language. The content of journal articles is usually substantiated with a bibliography.  Most journal articles list the authors' name and sometimes their academic credentials and institutional background, as well.  Journals tend to be very text oriented, without a lot of pictures or advertisements. Journal articles are what you use for college level research!

Magazine articles tend to be more accessible, general, and appealing to the public-at-large.  Many magazine articles will not list authors.  Most magazine articles will not include bibliographies.  Magazines have pictures and advertisements.   Generally, you do not want to use magazine articles for college level research.