How far is history a science ?
For the most part, history is not a science. There are at least two ways in which you can argue that it makes use of science and scientific ideas, but it is not itself a science.
History often makes use of scientific discoveries. For example, the use of carbon dating is very common in the study of history. The process of carbon dating is scientific. History also makes use, to some degree, of the scientific method. That is, historians can come up with hypotheses and then examine the evidence to determine whether their hypotheses are correct.
But this is where the similarity ends. Historians can try to test hypotheses by looking at evidence, but the evidence that they have to look at is generally subjective and open to interpretation. The answers to most historical questions cannot be objectively found by looking at evidence. Instead, they have to be subjectively interpreted by looking at that evidence. For example, if I wish to discover whether the US or the USSR was more at fault for the outbreak of the Cold War, I cannot find data that will objectively tell me this. Instead, I have to look at what happened and what was said at the time and I have to interpret that “data” to try to determine the answer.
Thus, history is only a science in very tangential ways.