SPECTROSCOPY AND THE STARS
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Background
Most of the objects we see in the everyday world are visible because they reflect ambient light into our eyes. These objects have color because they are made of materials that reflect certain wavelengths of light better than others. However, materials that are heated or otherwise injected with energy can also release this energy as light. The characteristics of this light can tell us the physical characteristics of the material.
Heating a dense gas or material will cause it to glow. This wavelength of radiation is randomized by collisions in the material and ends up spread across a broad range of wavelengths, but peaks at a wavelength systematically related to the temperature.
Heating a dense gas or material will cause it to glow. This wavelength of radiation is randomized by collisions in the material and ends up spread across a broad range of wavelengths, but peaks at a wavelength systematically related to the temperature.
Gases that are heated up, or receive electrical current, release that energy at discrete frequencies which cause white light to split into bands. This pattern of spectral lines is unique to each compound. This occurs because electrons in an atom are constrained to specific orbits, each of which has a particular energy. The energy of a photon depends on its frequency, and atoms can only absorb or release photons with energies with the right amount of energy to shift one of their electrons to another available energy level.
Emission Spectrum
Atoms of different elements, such as helium and nitrogen, have different allowable energy levels for their electrons. This produces different spectral lines for each atom. These spectral lines can appear as lines of color on a dark background, and this is called emission spectrum. If a source of continuum radiation shines through the gas, some of the radiation will be absorbed by the gas and scattered out of the line of sight. This produces a spectrum with dark spectral lines, or an absorption spectrum. Some sample spectra are shown below.
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Using a Spectrometer
You can use a spectrometer to measure the spectrum of each fluorescent bulb, just like a telescope can see these bands from across the galaxy and reveal the composition of celestial bodies, we can also determine what is the composition of the gas inside the bulb.
Using our worksheet, you will observe the different frequencies of light produced by different light bulbs. Modern fluorescents try to simulate daylight conditions by producing colors of various "temperatures". A fluorescent bulb actually contains a mixture of electrically excited gases that produce light at a number of narrow frequencies. Our eyes, however, are poor spectrometers and thus perceive this light as "warm" or "cool" light. What bands do you see on your spectrometer?
Using our worksheet, you will observe the different frequencies of light produced by different light bulbs. Modern fluorescents try to simulate daylight conditions by producing colors of various "temperatures". A fluorescent bulb actually contains a mixture of electrically excited gases that produce light at a number of narrow frequencies. Our eyes, however, are poor spectrometers and thus perceive this light as "warm" or "cool" light. What bands do you see on your spectrometer?
