Although a grand design spiral, M101's has a distinctly off center core and far flung spiral arms, likely from tidal interaction with some of its known satellite galaxies. M101 has a diameter of 170,000 light-years and is 21 million light-years away. Exposures: L:R:G:B=275:80:75:75 minutes=8 hours 25 minutes total exposure at f/8.3.