9
Spectral
Measurements
•Use
spectra of stars
•Ignore
broad (“high pressure” stellar lines
•Very
narrow (low pressure) lines from interstellar gas
–This
one Ca II = Ca+1
•Stronger
in more distant stars
•Stronger
when looking through
interstellar gas clouds
•Hydrogen
hard to measure
–remember
Balmer rules
From our text: Horizons, by Sees