and the story behind the Rockwell Painting
The occasion depicted in this Rockwell painting is the 1858 murder trial of an Illinois man named William "Duff" Armstrong. Armstrong was accused of murdering James Preston Metzker with a “slung-shot" - a weight tied to a leather thong, sort of an early blackjack - a few minutes before midnight on August 29, 1857. Lincoln was a friend of the accused man's father, Jack Armstrong, who'd just died, and so he offered to help defend young Duff Armstrong, without pay, as a favor to Jack Armstrong's widow.
The principal prosecution witness against Armstrong was a man named Charles Allen, who testified that he'd seen the murder from about 150 feet away. When Lincoln asked Allen how he could tell it was Armstrong given that it was the middle of the night and he was a considerable distance away from the murder scene, Allen replied, "By the light of the moon."
Enter the Almanac!
Upon hearing Allen's testimony, Lincoln produced a copy of the 1857 edition, turned to the two calendar pages for August, and showed the jury that not only was the moon in the first quarter but it was riding "low" on the horizon, about to set, at the precise time of the murder. There would not have been enough light for Allen to identify Armstrong or anyone else, said Lincoln. The jury agreed, and Duff Armstrong was acquitted.