Coronium and nebulum
The chemical composition of all common stars is very much the same, so their spectrum depends on the surface temperature. For example, in the visible range of the sun spectrum two absorption lines of ionized calcium are seen best, which certainly does not imply that the sun is made mostly of calcium. It is the conditions on the sun that cause the minimal amount of calcium to manifest its presence so strongly.
When spectral analysis was applied to the light of heavenly bodies, it was soon discovered that the corona of the sun emits spectral lines of some unknown element. For lack of better ideas, it was given the name of coronium. On the other hand, similar lines of another unknown element were found in the spectrum of planetary nebulae. The element was called ... nebulum, of course. Unfortunately, there was no room in the Mendelyeev table for these two elements, so the conclusion could be no other than the following: the lines come from known elements subject to unusual conditions. It turned out that the "coronium" consists of metals ionized more than ten times due to the extremely high temperature of the corona (over 1,000,000 K). The "nebulum", in turn, proved to be composed of known heavy elements in a state of rarefaction unattainable in a laboratory. It is in this state that the atoms can indeed emit so-called forbidden lines that correspond to transitions between enrgetic states which do not occur at greater gas density, when they are destroyed by frequent collisions.