Portal:Radiation astronomy/Topic/3

Absorptions

Main articles: Radiation astronomy/Absorptions and Absorption astronomy

A spectrum is taken of blue sky clearly showing solar Fraunhofer lines and atmospheric water absorption band. Credit: Remember the dot.

"[P]referential absorption of sunlight by ozone over long horizon paths gives the zenith sky its blueness when the sun is near the horizon".

"For quenched galaxies, the Hα absorption trough is deep and can be traced through the nucleus and along the major axis. It extends to a radius at or beyond 2 R_d [where R_d is the galaxy disk scale length] in all but three cases. This makes it possible to determine a velocity width from the optical spectrum as is done for emission line flux, with appropriate corrections between stellar and gas velocities (see discussion in Paper I, also Neistein, Maoz, Rix, & Tonry, 1999). In the few cases where a velocity width can also be measured from the H I data, it is found to be in good agreement with that taken from the Hα absorption line flux."