David Bowie's hauntingly beautiful Blackstar was the artist's final gift to us all, shortly before he died last year. But as it turns out, there was one final surprise hidden in the gatefold cover of his last LP. One Redditor discovered that if you expose the cover for Blackstar to the sun, it changes from the standard black design to one showing a starfield. According to another post on the same thread, the effect is seen when a bright light is shined through the back of the cover, since a difference in the thickness of the paper causes a bleed-through of the starfield on the inside of the cover.
In an interview with designer of the cover Jonathan Barnbrook at the time of the album's release, Barnbrook said Bowie "always wanted to do something interesting, often to the annoyance of the record company". I guess this qualifies.
Image: David Bowie/BoldlyGettingThere