Mackay, Scott. "Threshold of Perception"
Divergence: 1910 CE
What if: What if Halley's Comet collided with Earth in 1910.
Summary: A French astronomer relates the history of the collision, from Percival Lowell's prediction to the subsequent invasion of stricken France by Germany's army.
Published: In Interzone #197 (Mar/Apr 2005).