Aug. 8 & 29 (different times). All invited to drop in and tour the historic building, view exhibits, participate in astronomy-related activities, and use the observatory’s telescopes (weather permitting). On Aug. 29, the observatory is open late to observe the night sky with the 1857 Fitz telescope. Noon–5 p.m. (Aug. 8) & noon–11 p.m. (Aug. 29), 1398 E. Ann at Observatory. Free. (734) 763–2230, detroitobservatory.umich.edu.