Second solar spectrum

These have broad effects 200 Å wide and show a sign reversal at their centers.

[1] Molecular lines with stronger polarization than the background due to MgH and C2 are common.

[1] Other odd lines include Li I at 6708 Å which has 0.005% more polarization at its peak, but is almost unobservable in the intensity spectrum.

What happens at the limb is that there is a forest of spicules poking out from the edge, so it is not possible to get parallel to such a rough surface.

[2] For most of the solar disk the degree of linear polarization of the continuum is under 0.1%, but it rises to 1% at the limb.

A visualization of the visible part of the solar spectrum (left) and second solar spectrum at the solar limb (right). The intensity spectrum is coloured to mimic a spectrograph observation, while the linear polarization is proportional to the brightness.