The most reliable knowledge is that acquired by the scientific method.
Four essential elements of the scientific method are iterations,
recursions, inter-leavings, or orderings of the following:
- Characterizations (observations, definitions, and measurements of the subject of inquiry)
- Hypotheses (theoretical, hypothetical explanations of observations and measurements of the subject)
- Predictions (reasoning including logical deduction from the hypothesis or theory)
- Experiments (tests of all of the above)
Wikipedia: Elements of the Scientific Method
So to gain knowledge scientists need to characterize the subject of inquiry. One possible term for this process might be "data collection" but you'll be hard pressed to find a better term than your own, as @RegDwigнt already commented
- 1.a. To be or become aware of, especially through careful and directed attention; notice: observed a car leaving the property.
- 1.b. To watch attentively: observe a child's behavior.
- 1.c. To make a systematic or scientific observation of: observe the orbit of a comet.
A great example of making observations over a long period of time was
Tycho Brahe, born Tyge Ottesen Brahe (14 December 1546 – 24 October 1601), was a Danish nobleman known for his accurate and
comprehensive astronomical and planetary observations. He was born in
Scania, then part of Denmark, now part of modern-day Sweden. Tycho was
well known in his lifetime as an astronomer, astrologer and alchemist,
and has been described more recently as "the first competent mind in
modern astronomy to feel ardently the passion for exact empirical