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WJP X, XXXX.XX (20XX) Wabash Journal of Physics 1 Observing the Solar Spectrum Daniel Brown and Micah Milliman Department of Physics, Wabash College, Crawfordsville, IN 47933 (Dated: November 7, 2008) The solar spectrum gives a lot of information about the elements that make up the Sun and that are used in the fusion reaction. We looked at solar spectrum using a MEADE LX-200 8 inch and a Red Tide spectrometer and found the spectral lines given by the elements. We found evidence of hydrogen, helium, nitrogen, dioxide, and oxygen. The Sun is the most prominent feature in our solar system. It supports all the planets and life forms in our solar system. The energy from the Sun that sustains us is created deep within the core of the Sun. The temperature and pressure there is much greater than on Earth and is the perfect conditions for nuclear reactions to take place. In the core of the Sun gravitational forces accelerate hydrogen atoms and make them collide. The collision causes hydrogen nuclei to fuse together to form a helium nucleus. This means that the Sun generates its energy by the nuclear fusion of hydrogen nuclei into helium. The helium atom is much smaller than the hydrogen and the difference in mass is expelled as energy in the form of a photon and is carried to the surface of the Sun. Through convection the light and heat is released into the atmosphere and felt on Earth as heat and light. This energy can be harnessed through many different natural and synthetic processes. Photosynthesis and solar cells use solar power to generate power and energy. Spectroscopic analysis separates light emanating from the Sun into a pattern of colors. This allows scientists get an idea of the proportional breakdown of elements that are present in burning solar masses. Each element is related to a specific wavelength according to its energy. The Sun’s spectrum ranges from 350 nanometers to 950 nanometers. Using this process we can confirm which elements make up the Sun and which are involved in the fusion reaction. The spectrum should mostly consist of hydrogen and helium lines. To observe the solar spectrum we used a MEADE LX200 8 inch, seen in FIG. 1. The telescope gave us a clear imagine of the Sun but the light was far to intense to look at directly. We added an 8 inch solar screen over the lens of the telescope so that we could view the Sun without damaging our eyes or flooding the measuring equipment. The solar screen blocks out all of the Suns light except for 1/10,000th. This allows us to safely view the Sun. We then attached a fiber optic adapter to the eyepiece of the telescope and a fiber optic cable that led to a Red Tide spectrometer, shown in FIG. 2. The spectrometer is an optical instrument used to measure properties of light over a specific portion of the electromagnetic spectrum. The spectrometer produces spectral lines and measures wavelength and intensity using a CCD camera. The data collected is then sent to LoggerPro were we plotted the results. To align the telescope with the Sun we first removed the solar screen and took FIG. 1: The figure shows the telescope that we used for this experiment. We used the MEADE LX-200 8 inch telescope. We placed a solar screen that allowed 1/10,000th of the light in over the 8 inch lens and looked at the Sun. We then connected the Red Tide spectrometer, shown in FIG. 2 to the telescope using a fiber optic cable and we were able to measure the solar spectrum of the Sun. off the eyepiece. We held a piece of paper up against the eyepiece hole and moved the telescope lens vertically and horizontally using the control knobs until the light on the paper was brightest. We then placed the solar screen over the lens and attached the fiber optics cable. The LoggerPro program was set to fast collect and we made small adjustments to the vertical and horizontal positioning and the focus until the intensity was maximized. We then changed the the collection period. We performed ten trials. The first five had collection periods of 1000 ms and the next five had collection periods of 600 ms. While examining our results we noticed that the data did not fit the exact shape that we expected. The Sun is a black body and the shape of the spectrum can be described by Planck’s Law I(λ, T ) = 2πc2 h 1 , λ5 ehc/λkB T − 1 (1) where λ is wavelength, T is temperature, c is the speed of light, h is Planck’s constant, and kB is Boltzmann’s constant. WJP X, XXXX.XX (20XX) Wabash Journal of Physics 2 in our data. Using the Basic Atomic Spectroscopic Data supplied by NIST, we identified helium, hydrogen, fluoride, dioxide, nitrogen, and oxygen spectral lines. All these elements are found in either the atmosphere of the Earth or the Sun. This means that our solar spectrum measurement is a good representation of the Sun. For future trials of this experiment their some improvements that can be made. More research should be done about the sensitivity of the CCD camera in the Red Tide spectrometer. There may be an adjustment that can be made or maybe a constant to multiply the data by. Also, it may be better to calibrate the data using a black body with a higher temperature than the incandescent light bulb. We suggest trying an arc lamp or a halogen light bulb We found that our raw solar spectrum data did not fit this. We attributed this difference to the response function of the CCD camera in the Red Tide spectrometer. To fix this difference we took data with an incandscent light bulb, which is also a black body. We placed the fiber optic cable in a dark box and collected spectrum data. We randomly changed the voltage to create a different temperature for each trial. We preformed this ten times using different voltages each time. We calculated the expected value using Planck’s law and divided it by the actual data to get the calibrated data. We then normalized this data by dividing by the maximum. We took the solar spectrum data and averaged tthe ten trials and normalized it by dividing by the maximum. We then multiplied the normalized calibrated light bulb data by the normalized calibrated solar spectrum data to get the final calibrated data. shown in FIG. 3. We checked the accuracy of our solar spectrum measurement and calibration by identifying the spectral lines [1] [2] [3] [4] He H O2 F N N O 0.14 0.12 0.1 Intensity (I) FIG. 2: This figure shows the schematic for the Red Tide spectrometer that we used for the experiment. Light enters the spectrometer from a fiber optic cable(1) and goes through a small slit(2). The light then passes through a filter (3) and reflects off a collimating mirror(4) that focuses the light. Next the light enters a diffraction grating(5) and directs the light towards a focusing mirror(6). Finally the diffracted light is incident upon the CCD camera(7) and the data is sent to LoggerPro.[4] 0.08 0.06 0.04 0.02 0 400 500 600 700 800 900 Wavelength (nm) FIG. 3: The graph shown in this figure shows the results the calibrated spectrum of the Sun. We calibrated this data to eliminate the response effects of the CCD camera. We can see the spectral lines that are emitted from the Sun and the spectral lines from the light interfering with the atmosphere. This lines were in agreement with NIST’s Basic Atomic Spectroscopic Data[1]. instead. physics.nist.gov/PhysRefData/Handbook/periodictable.htm and Operation Manual”, Ocean Optics, Inc., Dunedin, FL, http://en.wikipedia.org/wiki/sun pages 20-21. http://www.solarviews.com/eng/sun.htm [5] www.meade.com Red Tide USB650 Fiber Optic Spectrometer, ”Installation