An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The strong → scattering that occurs in a fluid near the → critical point. Large density fluctuations bring about inhomogeneities of all sizes. This results in the scattering of light at all wavelengths giving a milky appearance to the fluid.

→ critical; → opalescence.

A → mineral, an amorphous form of → silica, SiO₂ with some → water of → hydration, found in many varieties and colors, including a form that is milky white.

M.E., from M.Fr. opalle, from L. opalus, from Gk. opallios "opal, gem;" probably from a source akin to Skt. upala "jewel, precious stone."

Loan from E., as above.

1) The state of being → opalescent, or emitting an → iridescence like that of an opal.
2) Physics: The milky → iridescent appearance of a dense transparent medium when it is illuminated by → polychromatic visible radiation (such as sunlight) due to local → fluctuations in its density and therefore in its → refractive index. → critical opalescence.

→ opal; → -escence.

Exhibiting a play of colors like that of the opal.

→ opal; → -escent.