Each spacecraft was equipped with removable window shades which were secured in place with hook and loop closure, and prevented the sun shining inside. Without the "safety layer" of 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" circular hatch window during the historical Apollo 11 first lunar-landing mission. It was transferred from NASA to the Smithsonian in 1970.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.