Question

The strongest lines in the solar spectrum are the Ca H and K lines which are produced by singly-ionized Ca atoms in the ground state. Show that, in the solar atmosphere (Teff = 5777 K, ne = 2

Answer 1

Although in the sun hydrogen is about a million times as abundant as calcium, the Ca II K line is much stronger (wider) than the H2 line.
The lines I compare are formed by calcium and hydrogen, the latter element being a million times as abundant as the first. The calcium line is caused by a transition from the first level of once ionized calcium to the second level. This corresponds with a wavelength of 3933.7Angstorm.
even though calcium is much less abundant as hydrogen in the sun's photosphere, the energy needed to get to the second level of hydrogen is too much, and therefor it rarely happens. Calcium on the other hand only needs about 7 eV to get to the second level of Ca+, which happens much more easily at 5800 K.Because the effort needed to get electrons to the right position in calcium is much less than in hydrogen, there are much more calcium ions with electrons in the ground level than there are hydrogen atoms with electrons in the second level. Therefore many more electrons are available to absorb photons for the calcium line than for the hydrogen line, and this means that the calcium line is wider.