ASTRONOMY 105 Observational Astronomy Lab D Instructions Lab D: The Solar Spectrum Part A: Determine the Scaling factor (completing Table 2 on worksheet) 1. Using the solar spectrum, (which is a good example of an absorption spectrum), measure the distance (in millimeters - mm ) between two widely spaced, "known" lines (See Table 2 on worksheet, one pair has been completed as an example). 2. Find the distance between these lines in nanometers ( nm ) using Table 1. 3. Divide the distance in nanometers, nm (step 2) by the distance in mm (step 1) to get the number of nanometers per mm. 4. Average the results of the four measurements to get the scaling factor. This has been filled in for you for the on-line version. 5. Part B: Calculate the wavelengths of the "unknown" lines (Table 4) Pick the K line of Ca II at 393.4 to serve as your reference line to measure the unknown lines. Fill in your reference line's designation, location (in mm), and wavelength on the data sheet. Table 1 -- "Known" Lines Designation Wavelength (nm) Origin A 759.4 terrestrial oxygen B 686.7 terrestrial oxygen C 656.3 hydrogen (Hα) D 1 589.6 neutral sodium (Na I) D 2 589.0 neutral sodium (Na I) E 527.0 neutral iron (Fe I) F 486.1 hydrogen (Hβ) H 396.8 ionized calcium (Ca II) K 393.4 ionized calcium (Ca II) ASTRONOMY 105 Observational Astronomy Lab D Instructions 1. Find the location of each of the unknown lines (numbered 1-5) in mm on using the scale below the solar spectrum. They are at the bottom of the solar spectrum, on the left. 2. Measure the distance (in mm) from the reference line to each unknown line. Write each distance in Table 4 under distance ( mm) . Some of the table has been filled in for you. 3. Use the scaling factor to find the distance in nanometers. (= scale factor x distance in mm). Write this distance down in( nm) in Table 4. 4. Add the distance in nm to the wavelength of your reference line to get the wavelength of the "unknown" lines. This has been pre-filled for you. 5. Compare these wavelengths to the list of lines in Table 5 on the worksheet and identify the "unknown" lines in Table 4. Your values may not exactly match those given in the table. Just find the closest match. Table 5 – Wavelengths of known elements