http://www.teachastronomy.com/astropedia/article.aspx?qid=334 http://www.teachastronomy.com/astropedia/article.aspx?qid=335 http://www.teachastronomy.com/astropedia/article.aspx?qid=336
http://www.teachastronomy.com/astropedia/article.aspx?qid=337 http://www.teachastronomy.com/astropedia/article.aspx?qid=338
http://www.teachastronomy.com/astropedia/article.aspx?qid=339 http://www.teachastronomy.com/astropedia/article.aspx?qid=340 http://www.teachastronomy.com/astropedia/article.aspx?qid=341 http://www.teachastronomy.com/astropedia/article.aspx?qid=342
http://astro.unl.edu/classaction/ismstarform.html