Changes

[[Comets]] are astral bodies composed of dust and ice.  As they approach the sun the increased temperature causes them to heat and shoot off jets of material, forming a "tail" pointing straight towards the sun. Most comets are in circular orbits out in the Oort cloud beyond Pluto. Some are in an [[ellipse|elliptical]] orbit around the sun, meaning that they will repeatedly enter orbits near the sun until they have evaporated.  Some are in a [[hyperbola|hyperbolic]] orbit around the sun, meaning that they will only come into the solar system once and will never return, moving on to other solar systems until they have evaporated or are captured in an elliptical orbit.

[[Comets]] are astral bodies composed of dust and ice.  As they approach the sun the increased temperature causes them to heat and shoot off jets of material, forming a "tail" pointing straight towards the sun. Most comets are in circular orbits out in the Oort cloud beyond Pluto. Some are in an [[ellipse|elliptical]] orbit around the sun, meaning that they will repeatedly enter orbits near the sun until they have evaporated.  Some are in a [[hyperbola|hyperbolic]] orbit around the sun, meaning that they will only come into the solar system once and will never return, moving on to other solar systems until they have evaporated or are captured in an elliptical orbit.

==Scientific dating==

==Scientific dating==

The closest material we have to hand, rocks formed in Earth's crust, has been subject to chemical alteration over time from volcanic action, so for accurate dating scientists use meteorites which have been free flying for billions of years before entering our atmosphere. Mass spectrometers are used to accurately identify and measure the different atomic isotopes making up a core sample from a meteorite. Different radiometric dating techniques from the same sample are used as a guard against possible contamination. The isotopic ratios of the sample correspond to the degree of atomic decay, accurately measuring the sample's age.

The closest material we have to hand, rocks formed in Earth's crust, has been subject to chemical alteration over time from volcanic action, so for accurate dating scientists use meteorites which have been free flying for billions of years before entering our atmosphere. Mass spectrometers are used to accurately identify and measure the different atomic isotopes making up a core sample from a meteorite. Different [[radiometric dating]] techniques from the same sample are used as a guard against possible contamination. The isotopic ratios of the sample correspond to the degree of atomic decay, accurately measuring the sample's age.

== External links ==

== External links ==