Photometry, The Art of Astronomy

Like many subject of sciences, study on astronomy depend on measurement. But, unlike any other branch of science, measurement on astronomy is quiet intricate, since in astronomy, measurement is dealing with the light, per se. In astronomy, object under investigation is the heaven bodies, such as variable stars, minor planets, extra-galaxies, supernovae, or extrasolar planets, as the name for fews contemporary objects in astronomy.

If the objects under investigation is within our grasp, we can measure the length, the weight, the heat, etc. But objects of astronomy are far far beyond our reach, so the question is how do we measure the objects? How far is the object of investigation from us? How old, how hot, how large, how do we know what is that?