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It is possible, particularly in dry, desert climates, for organic materials such as from dead trees to remain in their natural state for hundreds of years before people use them as firewood or building materials, after which they become part of the archaeological record.
Thus dating that particular tree does not necessarily indicate when the fire burned or the structure was built.
The technique often cannot pinpoint the date of an archeological site better than historic records, but is highly effective for precise dates when calibrated with other dating techniques such as tree-ring dating.
An additional problem with carbon-14 dates from archeological sites is known as the "old wood" problem.
In their investigation, the ancient astronomers needed tools to evaluate their observations, which are not commonly used on more earthly problems.
One such tool is the concept of the magnitude, which Greek astronomer Hipparchus used about 200 years ago.
However, it does not give a measure of the intrinsic brightness of the object.
The apparent magnitude of the same object observed in the infrared band is different from the amount observed in visible light.
However, the concept is mainly used for observations in the visible region of the electromagnetic spectrum. Absolute magnitude is defined as the apparent magnitude of a star at the distance of 10 parsecs or 32.6 light years.
Particular isotopes are suitable for different applications due to the types of atoms present in the mineral or other material and its approximate age.
For example, techniques based on isotopes with half lives in the thousands of years, such as carbon-14, cannot be used to date materials that have ages on the order of billions of years, as the detectable amounts of the radioactive atoms and their decayed daughter isotopes will be too small to measure within the uncertainty of the instruments.
• The absolute magnitude is an intrinsic measurement, but apparent magnitude is not.