SpectraThe spectra observed from galaxies are formed from a combination of stars, molecular clouds, and star-forming regions. We can examine them to determine many properties, among them the radial velocity of the galaxy, the star-formation rate, and the average age and metallicity of the stellar populations, and the kinematics (mass) of the galaxy. A spectrum has three components: the continuum, absorption lines, and emission lines. Show
Solar spectrum
The diagram below shows how one could observe a continuum spectrum, and emission spectrum, or an absorption spectrum from different positions around a continuum source partially shrouded by a cool gas cloud.
The spectrum of celestial bodies tells astronomers what kind of substances are found in the inside of the star or planet as well as what kinds of gases are surrounding it. This information is helpful in comparing both atmospheres between Earth and other planets in our galaxy as well as comparing the composition of other stars with our Sun. In order to collect this data, a spectroscope is used to capture the light. Once the light is broken up into its constituent wavelengths, a spectrum is produced. There exist three types of spectrum important for review in Astronomy. These three types of spectra are organized into a series of laws relating both concepts of emission and absorption, known as Kirchhoff's Laws of Spectroscopy. Gustav Kirchhoff and Robert Bunsen were the first physicists to deduce the the meaning of the patterns produced by spectra1. Figure 1 below is an example of such spectra produced by the sun in which there is a clear variety of wavelengths represented by the spectrum of colors as well as a series of dark lines of different widths.2  Figure 1 Spectra of the Sun. Since the mid 19th century, scientists understood the range of colors appearing in a spectrum like this corresponded to the range of wavelengths the light source was emitting. The dark bands splitting the colors, called Fraunhofer lines after the man who first noticed them, were however a mystery. Kirchhoff and Bunsen set forth to determine the meaning of these dark bands in spectra. Upon creating a makeshift spectroscope including an observing telescope, prism, and Bunsen's own burner to produce light (figure 2), Kirchhoff developed a three piece law series from which astronomy has lain its foundation.1 Figure 2. Spectroscope created by Gustav Kirchhoff and Robert Bunsen Kirchhoff deduced that hot solids, liquids, and gases under high pressure radiate a continuous spectrum, the black body radiation curve. He also noted hot gases under lower pressure produce tiny peaks of color throughout a spectrum, called emission lines or bright line spectra. The energy emitted by these molecules due to their kinetic motion is not enough to create a full spectrum targeting each wavelength, but small portions of the spectrum. Lastly, he realized that cooler gases surrounding the object in focus absorb some of the energy being released by the black body radiating. Thus, a spectrum where some wavelengths are omitted in the form of tiny dark bands are produced.1 These are known as absorption or dark line spectra because of their appearance.
Kirchhoff's Laws
Figure 3. Kirchhoff's Law's Illustrated.4 Stars, nebulae, and planets in space produce a continuous spectra because of the heat energy they radiate. The dark lines in the spectra produced from the absorption of some of the energy serve as evidence that cooler gases surround the bodies.3 The energy an electron absorbs to jump to the next level equals the amount of energy re radiated when the electron falls back to the ground state. In this way, astronomers can assume the gases absorbing the black body's radiation will produce a brightline spectrum in the same areas as the darkline spectrum.3 By measuring the wavelengths of radiation, an astronomer can tell what type of gas is surrounding the radiating celestial body. As we have discussed, hot bodies radiate much more energy than what simply exists in the visible spectrum. As such, astronomers need a system to measure spectra that cannot be seen. Spectra is often recorded in three series, Lyman series, Balmer series, and Paschen series.3 Each series corresponds with the transition of an electron to a lower orbit as a photon is emitted. Using the hydrogen atom as a model, astronomers have named the spectra recorded during a transition of an electron to the ground state, the Lyman series.3 This series records emission wavelegths in the ultra violet region because the energy and wavelength emitted is so powerful. The transition from an excited electron to the second level is not quite as big a jump and so it can be recorded in the visible spectrum above.3 The third series records emission lines from transitions to the third orbit, a much smaller jump resulting in the longer weaker waves of the infrared spectrum. These three series of spectra are important in examining the physical and chemical properties of both stellar and glaxy spectra. Figure 4 illustrates the three series in the emission spectra below. Figure 4 Lyman, Balmer, Paschen Series
Lastly, It is important to know that the spectra viewed by modern astronomers is digitally recorded as the spectroscope is aimed at a celestial body. Instead of bands of light, the scientist receives a graph comparing intensity and wavelength. These graphs will have sharp inverted peaks at the wavelengths of maximum energy. If you were using a spectrometer to observe the light radiating from an incandescent bulb you would see a continuous spectra. *What might happen if a cloud of cool gas was surrounding the light bulb? *What would you see if you turned the telescope side ways to capture the cloud of gas surrounding the bulb only? Which series would I be examining if a celestial body is radiating a 100nm wavelength? Examine the spectra of many common elements here. Back to Main Page References: 1. Walker, J. Light and its Uses: Making and Using Lasers, Holograms, Interferometers, and Instruments of Dispersion. W.H. Freeman: San Francisco, 1980; pp 93, 106 What are 3 types of spectra and how do they differ?The first spectrum is a continuous collection of wavelengths from the radiation of a heated body. The second is a brightline emission spectrum illustrating the wavelengths a particular gas emits. The third is a darkline absorption spectrum showing the wavelengths that would be aborbed if the gas above were cooled.
What are the 3 types of spectra produced by atoms?There are three types of atomic spectra and they are emission spectra, absorption spectra, and continuous spectra.
What is spectra and its types?A spectrum is defined as the characteristic wavelengths of electromagnetic radiation (or a portion thereof) that is emitted or absorbed by an object or substance, atom, or molecule. Examples of a spectrum include the rainbow, the emission colors from the Sun, and the infrared absorption wavelengths from a molecule.
Which of the three types of spectra is the Sun's spectrum?The spectrum of the Sun appears as a continuous spectrum and is frequently represented as shown below. This type of spectrum is called an emission spectrum because what you are seeing is the direct radiation emitted by the source.
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What are the 3 different types of spectra?
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