Introduction:

To the naked eye, stars and planets look white in color. In reality though, they are many different colors. By finding out what those colors are, you can figure out what the composition of the star is, and how much of each different element the star is made up of. This is done using spectroscopy.

Spectroscopy is using a spectrometer to find the spectrum. "The distribution of energy emitted by a radiant source, as by an incandescent body, arranged in order of wavelengths." (www.dictionary.com)

Hypothesis:

Apparently the most abundant element found in stars is hydrogen. Therefore, I expect that the emission spectrum of a star would closely resemble the emission spectrum of hydrogen.

Procedure:

Find the position of your star using the altitude and azimuth co-ordinate system. Altitude uses the horizon as the starting point (90 degrees being straight up). Azimuth uses north as the starting point (0 degrees) and turns clockwise. After finding your star, use the spectrometer to collect the light. The light from the star will be collected through a small slit in the spectrometer, then pass through a grid that which splits the light into it's various wavelength components (the same way a prism splits white light into it's various components).

Fig. A. The light path through the spectrograph makes many turns on its way to the camera's CCD chips (From Sky & Telescope Magazine, May 2000).

Each element has it's own specific spectrum. By comparing a standard spectrum to the spectrum of the star, you can decide which elements are present in the star. For example, Fig.1 shows the spectra of mercury and argon that can be seen with a commercially available spectrograph.

Fig.1: Low resolution spectra of a calibration lamp containing mercury and argon. and argon that can be seen with a commercially available spectrograph (From Sky and Telescope magazine, May 2000).

Figure 2 shows the emission spectra of various stars.

Fig 2: Examples of emission spectra of the following stars (from top to bottom): Castor, Procyon, Capella, Pollux and Betelgeusse. (From Sky and Telescope magazine, May 2000)

The emission spectra in Fig. 2 are centered at the 4861 angstrom line of hydrogen.

Fig. 3 shows the emission spectrum of atomic hydrogen (a) and molecular hydrogen (b)

Fig. 3 a. The emission spectrum of atomic hydrogen consists of a few widely spaced bands. b. molecular hydrogen gives of light at more frequencies and thus has more bands in its spectrum (From Chemistry by Addison-Wesley).

Word Count: 411