event-horizon
Explanation
The Joke
The comic depicts the aftermath of a duel at dawn. One man lies dead on the ground while another stands over him, still holding a pistol. An astronomer character explains his defense: "Look, I know it's still dark out, but the geometric center of the sun's disc was precisely eighteen degrees below the horizon, and it's not my fault if Jones wasn't ready at the marked time." The caption reads: "Never challenge an astronomer to pistols at dawn."
The joke is that "dawn" is an imprecise term in everyday language, but astronomers have very specific technical definitions for different stages of twilight. Astronomical dawn occurs when the sun's geometric center is 18 degrees below the horizon -- a point at which the sky is still essentially dark to the naked eye. The astronomer exploited this technicality, showing up and firing at "astronomical dawn" (when it was still pitch dark) before his opponent could even see him.
The Humor
The comedy comes from the lethal consequences of astronomical pedantry. The astronomer is technically correct -- he did appear and fire at dawn, by the most rigorous astronomical definition -- but this is clearly not what anyone means when they say "pistols at dawn." The image of a man lying dead because his opponent used a niche technical definition of sunrise is darkly funny. It also plays on the stereotype of scientists and academics being insufferably literal and using their specialized knowledge for personal advantage in unexpected ways.
References
- Astronomical dawn, nautical dawn, and civil dawn are three formally defined stages of twilight, occurring when the sun is 18, 12, and 6 degrees below the horizon, respectively. At astronomical dawn (sun 18 degrees below the horizon), the sky is still quite dark.
- Dueling at dawn was a common convention in historical duels, chosen partly for the symbolic significance and partly for practical reasons (good light, fewer witnesses).