An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 3 Search : depth
depth
  ژرفا   
žarfâ (#)

Fr.: profondeur   

Noun form of → deep. → optical depth.

From M.E. depthe, from O.E. deop "deep," → deep + -the "-th."

Žarfâ, noun of žarf "deep," → deep + .

equivalent depth
  ژرفای ِ هم-ارز   
žarfâ-ye ham-arz

Fr.: profondeur équivalente   

A measure of the number of particles passing a given point in a → planetary ring per unit time. It is obtained by multiplying the physical width of the ring by its average → optical depth. For the variable-width eccentric rings of → Uranus, equivalent depth remains almost constant around a given ring (Ellis et al., 2007, Planetary Ring Systems, Springer).

equivalent; → depth.

optical depth
  ژرفایِ نوری   
žarfâ-ye nuri

Fr.: profondeur optique   

1) A measure of how much radiation is absorbed when traveling through a medium (such as the atmosphere of a star or the interstellar medium) from the source to a given point. It depends on the type of medium and the frequency of radiation. It is defined as a dimensionless quantity λ = κλ ρ dx, where κλ is the extinction coefficient, ρ the density, and dx the path length.
2) The ratio of the intensity of radiation (light or radio waves) incident on a ring to that emerging from the opposite face of the ring, expressed as a natural logarithm. If the reduction in intensity is by a factors of e (= 2.718), the ring is said to have an optical depth of 1. Normal (or normalized) optical depth is optical depth corrected for oblique (non-vertical) viewing. In ring studies, the terms optical depth and optical thickness are generally used interchangeably. These terms generally refer to a particular wavelength (Ellis et al., 2007, Planetary Ring Systems, Springer).

optical; → depth.