Observational Science vs. Historical Science?

2016 Note: This post was written addressing the distinction between observational science and historical science as Ken Ham and many young-earth creationists understand it. Their understanding of the concepts and their distinction are INCORRECT, but they are common in Christian circles, so they must be addressed. After reading this critique and seeing the highlighted problems with their distinction, please read my chapter-by-chapter review of the book that originally defined the terms and described the proper distinctions between them (Origin Science by philosopher Norman Geisler). The proper distinction does not fall prey to the critiques in this post, thus I do support the distinction between the terms, but ONLY as the terms are properly understood and properly distinguished.

Introduction
It is quite common to hear in Christian discussions about science that there exists a distinction between observational science and historical science. This distinction took center stage in Ken Ham's debate with Bill Nye one year ago (see here). Ken Ham is a young-earth creationist, who often appeals to this distinction to undermine the evidence that supports any age of the universe that is older than what he believes it to be (6000 to 10000 years). Bill Nye, as well as the majority of the scientific community, rejects such a distinction, though, so Ham's critiques based on this distinction are rarely taken seriously. For Christians who wish to demonstrate evidence for the truth that God created the universe, this distinction often stands in the way of their being taken seriously by those who offer scientific evidence against a young universe and earth. If this distinction is one that is not true, then Christians need not defend this stumbling block that stands between their scientifically minded friends and those friends' salvation. I decided to do a search for a piece that might explain the distinction a bit more on Ham's site before I critiqued the distinction. This is what I found: "Deceitful or Distinguishable Terms—Historical and Observational Science." Please read it to ensure that I am accurately representing the claims of the author in this critique.* Ken Ham recently posted a blog post the other day that appeals to this distinction. It may be read here. I also checked to see if those at the Institute for Creation Research (ICR) subscribe to this distinction, and they do; their article can be found here.