Relative dating involves radioactive isotopes
Do some reading on "radioactive dating" or "radiometric dating" for more details - for example, in the Wikipedia.
Radioactive elements tend to degrade or give off radiation at a constant rate.
Relative dating, meanwhile, measures the order of past events, without determining their absolute age.
Radiometric dating--the process of determining the age of rocks from the decay of their radioactive elements--has been in widespread use for over half a century.
The Hubble Telescope can detect objects having an apparent magnitude of up to 31.5.
brighter to observers on Earth if it is simply situated closer to the Earth, whereas a distant star, which is in fact very luminous, might seem faint. Sirius is a star which is comparatively much more luminous than the Sun. The absolute magnitude of an object is defined as the brightness of an object at a distance of 10 parsecs away from it.
Apparent magnitude is a measurement of how bright an object seems at the point where it is observed.
Radioisotopes decay into other elements at a fixed and known rate.However, because it is much farther away from Earth, it appears much fainter. (A parsec is a unit used to measuring distances between stars.A parsec is about 3.26 light years, and the distance between the Sun and Proxima Centauri, the closest star to the Sun is about 1.3 parsecs). Apparent magnitude gives the brightness of an object, observed from any point.So, if you know how much of the radioactive isotope is still left in the sample, then you can work out how long it would have taken for the rest to have decayed into other…By far the most common is radioactive dating which involves checking the amount of a given radioactive isotope in a given sample is left over (and calculating from the half-life [the time it takes for a radioactive element/isotope to decay to half the original amount]).