... The extinction in terrestrial atmosphere. ... A star was observed at different zenith distances during one night at the Engelgardt's Astronomical Observatory in the program of atmospheric extinction study at blue. ... Calculate the air mass for given zenith distances in 1st 54.9 11800 column, and write the result into the 2nd column. ... Spectral observations. ... Calculate the radial velocity Vr of the star on each date, the results of measurements and write calculations into the table. ...