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# Spectral Lines of Hydrogen

## Emission lines are related to electron transitions.

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Deciphering the Sun

### Deciphering the Sun

Credit: AER Wilmington DE
Source: http://www.flickr.com/photos/25949441@N02/9616918091
License: CC BY-NC 3.0

You may have learned that the Sun is made up of mostly hydrogen and helium. Before accepting this as fact, think about it. How do we know this to be true? No one has been to the Sun, and no unmanned spacecraft have returned from the Sun. However, there is something from the Sun that is available in abundance here on Earth – sunlight. By analyzing the light that the Sun emits, we can obtain a large amount of information, including what elements are present.

#### Amazing But True!

• Essentially all of the information we have about stars comes from analysis of the light they emit, including both visible and non-visible electromagnetic radiation.
• Credit: NASA
Source: http://en.wikipedia.org/wiki/File:The_Sun_by_the_Atmospheric_Imaging_Assembly_of_NASA%27s_Solar_Dynamics_Observatory_-_20100819.jpg
License: CC BY-NC 3.0

This is a false-color image of the Sun observed in the extreme ultraviolet region of the spectrum [Figure2]

• The extremely hot center of a star emits a continuous spectrum. However, some of this light is absorbed by cooler atoms on the surface of the star. By matching these absorption patterns to known atomic absorption spectra, we can determine the relative abundance of various elements in the star.
• Learn more about using emission and absorption spectra to analyze starlight by watching the following video:

#### Explore More

With the links below, learn more about electromagnetic radiation and absorption spectra. Then answer the following questions.

1. Atomic hydrogen has a strong absorption band at a frequency of 2.45×1015 Hz\begin{align*}2.45 \times 10^{15} \ Hz\end{align*}. What is the wavelength of this band? Is this wavelength visible to humans?
2. What percentage of atoms in the Sun are either hydrogen or helium?
3. Various bands in the solar spectrum are labeled at the following website: http://www.harmsy.freeuk.com/images/spectrum.jpeg. Which four lines correspond to hydrogen absorption bands?
4. A spectrum of the Sun taken at the Palomar observatory in southern California has more absorption bands than one taken by the Hubble Space Telescope. Why might this be the case?

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