Each spacecraft was equipped with removable window shades which were secured in place with hook and loop closure, and prevented the sun shining inside. Above the Earth's atmosphere, the sun's light is strong and periodically required blocking (for sleeping, etc.).
This shade was used in Command Module "Columbia's" right side rendezvous window during the historical Apollo 11 first lunar-landing mission. NASA transferred it to the Smithsonian in 1970.
Transferred from the National Aeronautics and Space Administration