| Just for fun I decided to estimate the apparent brightnesses of stars that were recorded in the M42 image on the previous page. Below are three images which illustrate the estimation method I used. First, I superimposed the locations of stars from the Smithsonian Astrophysical Observatory (SAO) database onto the image and then digitized the locations of stars that appeared on the image but not in the SAO database. These stars are marked with green circles in the first image below. SAO stars are marked with diamonds. I then correlated the apparent stellar image widths and areas of the SAO stars with their corresponding visual magnitudes from the SAO database. After testing several fitting functions, it appeared that a simple linear fit of stellar image width to visual magnitude worked as well as any that I tried, particularly for the purposes of this exercise. A plot of image width vs. measured visual magnitude appears in the second image below. Using a "best-fit" linear fitting function, I estimated the visual magnitudes of the non-SAO stars and plotted the resulting values adjacent to each star in the third image below. Applying this method to all stars that were clearly visible in a high resolution scanned image of the negative, the lowest estimate of visual magnitude was approximately 11.5. |
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