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While trying to convert ecliptic coordinates from mean equinox of date to true equinox of date, I ran into excessive overhead from the IAU2000B nutation model. The fact that it uses 77 trigonometric terms made the calculations a lot slower. https://apps.dtic.mil/sti/pdfs/AD1112517.pdf Page 4 in the above document mentions a shorter series “NOD version 2” that has 13 terms instead of 77 as used in IAU2000B. I had not noticed NOD2 before, because it appears only in the FORTRAN version of NOVAS 3.x, not the C version. After reading the FORTRAN code, I realized NOD2 is the same as IAU2000B, only it keeps the first 13 of 77 terms. The terms are already arranged in descending order of significance, so it is easy to truncate the series. Based on this discovery, I realized I could achieve all of the required accuracy needed for Astronomy Engine by keeping only the first 5 terms of the nutation series. This tremendously speeds up nutation calculations while sacrificing only a couple of arcseconds of accuracy. It also makes the minified JavaScript code smaller: Before: 119500 bytes. After: 116653 bytes. So that's what I did here. Most of the work was updating unit tests for accepting slightly different calculation results. The nutation formula change did trigger detection of a lurking bug in the inverse_terra functions, which convert a geocentric vector into latitude, longitude, and elevation (i.e. an Observer object). The Newton's Method loop in this function was not always converging, resulting in an infinite loop. I fixed that by increasing the convergence threshold and throwing an exception if the loop iterates more than 10 times. I also fixed a couple of bugs in the `demotest` scripts.