Hey Nicole, your math looks right to me. However, another way to look at is that, given your 0.77 arcsec/pix image scale, Polaris will have moved roughly 7 pixel widths, which is well below the FWHM of Polaris. That said, celestial north is just to the left of this crop, so stars near the upper and lower right corners will have moved the most. The stars in the lower right corner are clearly elongated, but does it add up?
The bottom right star is SAO 548, at 88.78 deg declination. It should have traveled about 12.5 pixel widths across your sensor. It's clearly elongated, but doesn't look like 12 pixels of smear. You would have to check the full res image. Also, bear in mind that the brightness of each pixel within a star trail is the integration of intensity at that point over the duration of the exposure. Pixels toward the center of the arc will have been exposed the that star's light longer than those near the ends. You might consider the expected star trail length to be the traverse length (12px in this case), minus the FWHM of the star, which appears to be several pixels in this case, leaving you with about a half dozen pixels of apparent smear. That seems to get you in the right ballpark.
Edited by rkinnett, 30 July 2020 - 05:22 PM.