Module 4: “The Message of Starlight” Assignment #6 – How We Use Spectroscopy To Determine Light Sources (Chris Martin) The goal of this assignment is to explore how spectroscopy is used by astronomers to identify the elements in distant stars and galaxies. (It is also used in all sorts of fields to identify chemical composition: think CSI Miami.) This is accomplished by taking advantage of the fact that the spectra of hot, tenuous gases exhibit emission lines not at all wavelengths (i.e., a continuum spectrum) but only at specific wavelengths (an emission-line spectrum). The emission lines present depends on two things: (1) the elements (atoms or molecules) in the gas and (2) the temperature of the gas. Since each element yields a different pattern of lines, we can identify the elements present in the gas from the spectrum. Physicists and astronomers have identified hundreds of ionized elements and molecules in objects out in space by comparing their spectra to the spectra of hot gases on Earth. In fact, helium, the second most abundant element in the Universe, was first discovered in the Sun (hence the name helium- from the root “helios” for the Sun) by its unique spectral characteristics before it was found on the Earth. In this assignment you are going to identify types of lighting by their spectra. You will need the Night Spectra Quest card. First practice using the spectroscope to see the spectra of different light sources: this is easiest to do at night. Use a digital camera to take images of the spectra produced by holding your diffraction grating in front of an incandescent lamp (ensure there is no overspill from other lights). Take images of outdoor lights and try and identify the type of light as shown on the Night Spectra Quest card. Send your pictures to Chris Martin and explain on the blog how you might use this activity with your students. The International Dark Sky Association, headquartered in Tucson (www.darksky.org) has lots of information about lighting issues. You will find more about spectra in the lab at http://www.ifa.hawaii.edu/~barnes/ASTR110L_F03/spectralab.html And you may like to compare your spectra with the spectra produced by individual elements in the periodic table at: (you can click between emission and absorption spectra) http://jersey.uoregon.edu/vlab/elements/Elements.html.

An example of a kitchen light