Earth Day: 1970 to the Present

Earth Day was first celebrated on April 22, 1970. Founded by former US Senator Gaylord Nelson as an environmental teach-in, Earth Day is now coordinated by Earth Day Network, with extensive programming and events around the world. In 2009, the United Nations also declared April 22 to be International Mother Earth Day, an observance that "recognizes a collective responsibility, as called for in the 1992 Rio Declaration, to promote harmony with nature and the Earth to achieve a just balance among the economic, social and environmental needs of present and future generations of humanity." Look magazine first published the ecology flag shown above on April 21, 1970.

The First Observed Black Hole

Scientists with the National Science Foundation (NSF) and the Event Horizon Telescope (EHT) announced on April 10, 2019 that they have obtained the first visual record of a supermassive black hole and its shadow. Utilizing an international network of eight ground-based radio telescopes, a collaborative team of more than 200 researchers captured images of the black hole at the center of Messier 87, a massive galaxy in the Virgo galaxy cluster. The black hole is some 55 million light years from Earth and has a mass 6.5 billion times that of the Sun. The results of the years-long effort were published in a series of six papers in The Astrophysical Journal Letters, and were announced in a joint NSF/EHT press conference.