Wikipedia:Selected anniversaries/August 18
- 293 BC - The oldest known Roman temple to Venus was founded, starting the institution of Vinalia Rustica.
- 1590 - John White, the governor of the Colony of Roanoke, returned from a supply trip to England and found his settlement deserted.
- 1868 - Pierre Janssen discovered helium while analyzing the chromosphere during a total eclipse of the sun. This was the first element detected in space before being found on Earth.
- 1877 - Asaph Hall discovered Phobos, the larger of Mars' two moons.
- 1941 - The T-4 Euthanasia Program in Nazi Germany was temporarily halted due to public resistance.