Hotter BBs emit a larger fraction of radiation at shorter wavelengths than cooler BBs. This law relates color to temperature provided that the emitting object is a BB or approximately so. Often, we use the Sun as a reference or where the suffix is the traditional symbol for the Sun. The binary star UT-301 consists of a blue and a red star emitting the same total amount of energy. The absorption lines of metals, such as calcium, are prominent in the solar spectrum.
Hydrogen lines are less prominent.
The electrons are constrained to move only in selected orbits. They are not like objects in orbit around a star free to select any orbit. Indeed, electrons should be thought of as waves not particles in this context. For our purposes, it should suffice to examine the hydrogen atom which consists of a single electron and a proton as a nucleus. We can number the allowed electron orbits 1,2,3,. . .