 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
� |
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
|
|