The line spectrum for hydrogen is shown above with lines in the ultra-violet and visible regions.

$$\begin{array}{|c|c|} \hline \text{n, order} & \text{energy (eV)} \\ \hline 1 & -13.57 \\ \hline 2 & -3.39 \\ \hline 3 & -1.51 \\ \hline 4 & -0.85 \\ \hline 5 & -0.54 \\ \hline 6 & -0.38 \\ \hline \end{array}$$

The pattern of line can best be explained looking at series of transitions down to a particular level.

Lines to the ground state or n=1 are called the Lyman series and are in the UV as they have the largest energy transitions with n=2 to n=1 being the least energetic and longest wavelength.

Lines to n=2 are called the Balmer series with four lines in the visible spectrum. These are

$$\begin{array}{|c|c|} \hline \text{transition} & \text{wavelength (nm)} & \text{colour} \\ \hline \text{n=3 to n=2} & 656 \text{ nm} & \text{red} \\ \hline \text{n=4 to n=2} & 486 \text{ nm} & \text{blue-green} \\ \hline \text{n=5 to n=2} & 434 \text{ nm} & \text{violet} \\ \hline \text{n=6 to n=2} & 410 \text{ nm} & \text{violet} \\ \hline \end{array}$$

The line spectrum for mercury is shown.

Each element has a unique spectrum which can be thought of as a finger print revealing the presence of the element in the light observed.

The spectrum of mercury does not follow a simple pattern like hydrogen.

The diagram above show different atomic absoprtion spectra.

The are used to match the unknown spectrum.

The helium absorption spectrum is seen in the continuous white light spectrum from the Sun.

The missing lines are seen as the cooler atmosphere of the Sun absorbs specific wavelengths of light as the white from the hot Sun passes through the Sun's atmosphere.

The absorptio spectrum is the same as the emission spectrum except the wavelengths are missing.

This was used to discover the existence of helium in light from the Sun.

Helium is now known to be very abundant in the universe as it is formed in all main sequence stars as a product of nuclear fusion that allows the stars to burn hydrogen.