Young-earth creationists define “operational science” as experiments and observations of natural phenomena that are performed in real time—that is, in the present. They consider the outcomes from operational science as trustworthy and reliable. Young-earth creationists define “historical or origins science” as observations of and experiments on the presently existing natural realm so as to infer what occurred in the past. Such inferences, they argue, are based on questionable assumptions, such as the presumption that the laws of physics do not change over the history of the universe, Earth, and life. Consequently, they conclude that the findings of historical or origins science are not trustworthy and reliable. This explains why Ken Ham and other leaders of young-earth creationist organizations insist that the Bible, and the Bible alone, provides reliable information about what happened in the past.
But this dichotomy that young-earth creationists present is a false one. They are correct in stating that only phenomena we scientists observe directly can be considered to be assumption-free. They are wrong, however, in concluding that all historical sciences depend on indirect observations.
Astronomy is a discipline where we observe the past directly. [Read it all here.]