Conclusions

Now that we can use energy levels to explain absorption spectra, we can return to the spectrum of our sample star. In a star a continuous spectrum is created as a result of an extremely hot environment. A layer of relatively cool gases surrounds the star. Light emitted by the star passes through these gases. Atoms of the gases absorb photons and move from a lower energy state to a higher one. Then, photons of certain energies are no longer present in the light. Thus, we see dark lines — the absence of certain energies — in the spectrum of our star.

An important conclusion from this analysis is that absorption spectra can be used to identify elements in much the same way as emission spectra. 19th Century scientists used this identification process when they looked at the spectrum of the sun.

Are both hydrogen and nitrogen present in the gases surrounding the star?

Do you have any lines that are not accounted for by either hydrogen or nitrogen?

The 19th Century scientists went through this same process. The full solar spectrum had many more absorption lines than shown in the figure. The scientists were able to identify elements that could have absorbed photons associated with almost all of them. They even identified metals such as iron in the gases surrounding the sun. But, when they got done, they had some lines that they could not associate with any atom. These lines were the same ones that you had left over.

They knew that absorption of certain energies meant the presence of a certain type of atom. But, they had never seen either emission or absorption at these energies. So, an element not detected (in the 19th Century) on Earth must be in the gases around the Sun. They named the element helium after the Greek word helios, which means sun.