March 13 links two milestones in the widening study of the natural world. In 1733, English chemist, natural philosopher, and theologian Joseph Priestley was born; he is famously credited with discovering oxygen and helped pioneer investigations into gases. In 1781, William Herschel discovered Uranus, the first planet found with a telescope and the first new planet identified since antiquity. One life and one observation mark different scales of inquiry: experiments probing the substances around us, and an instrument extending the known solar system. Together, they make this date a reminder that scientific understanding grows through careful investigation and a willingness to revise the boundaries of what is known.
The same date also carries a stark political contrast. In 1868, the U.S. Senate began President Andrew Johnson’s impeachment trial after his violation of the Tenure of Office Act; in 1881, members of the revolutionary organization Narodnaya Volya assassinated Russian Tsar Alexander II in St. Petersburg. One event turned on constitutional process, the other on revolutionary violence, but both reflect struggles over authority and its limits. In the Northern Hemisphere, March sits at the threshold of spring, a season associated with change—a fitting backdrop for a list in which discovery, institutional conflict, and upheaval share a date. The entries also span nearly a century and a half, showing how a calendar day can gather very different turning points without making them part of a single story.