Observation is an activity of an intelligent living being (e.g. human), which senses and assimilates the knowledge of a phenomenon in its framework of previous knowledge and ideas.
Observation is more than the bare act of observing: Observation requires observing and seeking knowledge, often through experiment.
Observations that come from self-defining instruments are often unreliable. Such observations are hard to reproduce because they may vary even with respect to the same stimuli. Thus they are not of much use in exact sciences like physics which require instruments which do not define themselves. It is thus often necessary to use various engineered instruments like: spectrometers, oscilloscopes, cameras, telescopes, interferometers, tape recorders, thermometers etc. and tools like clocks, scale that help in improving the accuracy, quality and utility of the information obtained from an observation.
The accuracy and tremendous success of science is primarily attributed to the accuracy and objectivity (i.e. repeatability) of observation of the reality that science explores.