Scholarship of Discovery
Double stars are celestial objects that allow for calculating the mass of stars by assessing their orbits. Stellar mass affects every current model of stellar evolution, but the most accurate double star orbits can take decades to record. Due to the long-term nature of such observations and lack of groundbreaking research in double star studies, professional astronomers are no longer focused on making these measurements, so amateur astronomers can pick up where professionals have left off. Amateurs can only do this if they can get the equipment that they need at prices they can afford. A personally-manufactured filar micrometer could fill this need. Astronomers use a filar micrometer paired with a telescope to take visual double star measurements. Unfortunately, current commercial filar micrometers are cost prohibitive for most amateur astronomers. This project sought to design, 3D print, test, and calibrate a filar micrometer that amateur astronomers could produce cost effectively.
Creo Parametric 3.0 and a ProJet MJP 3600 Series 3D printer were used to design and print the filar micrometer. A Fowler 1-2” digital counter micrometer, 54-gauge Nichrome 80 wire, and a 6” Orion SkyQuest Dobsonian telescope were used with the printed filar micrometer to take measurements. The measurements were of the separation between components of an artificial double star created by flashlights reflected in a bearing ball. These measurements were used to calibrate the filar micrometer and find the preliminary accuracy of the filar micrometer.
Twenty-one measurements were taken of three different arrangements of the artificial double star. The average calibration calculated from this data is 1.44E-4 inches per arcsecond. Measurements of the 24 Coronae Borealis simulated star (with a separation of 20.14 arcseconds) produced a 17 percent error with an average measured separation of 16.74 arcseconds.
Though there is no firm standard, according to multiple sources a professional-quality filar micrometer should be capable of precision to one tenth of an arcsecond when measuring close double stars or one arcsecond for wider double stars. The filar micrometer produced in this project is capable (by design) of precision to seven tenths of an arcsecond. This means that it cannot reach the accuracy of the very few professional filar micrometers available for resale when measuring close double stars. However, at a tenth of the cost of the professionally-produced version, it is an affordable amateur filar micrometer. Since these are preliminary values for the calibration and accuracy of the produced filar micrometer, future data collection in these areas will lead to a better view of the true calibration value and accuracy possible for this filar micrometer.
Rull, Emily, "3D Printed Filar Micrometer" (2018). Honors Program Projects. 94.
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