شکست ِ دگرسانهای šekast-e dagarsâneyi
*Fr.: refraction différentielle*
A problem encountered in astronomical spectroscopy, which consists of a loss of light from
some wavelengths due to → *atmospheric dispersion*.
In simple terms, differential refraction means that at nonzero
→ *zenith distance*s an object cannot be simultaneously placed at
the same position within a → *slit* at all wavelengths. This problem
becomes more important for increasing → *airmass*, larger
→ *spectral range*, and smaller
→ *slitwidth*s. To remedy this drawback, the slit should always
be oriented along a direction perpendicular to the horizon, since differential
refraction occurs in that direction. → *differential*; → *refraction*. |