John Glenn, an astronaut who was the first American to orbit the Earth [1], died on Dec. 8. Glenn was both an astronaut with an incredible career and a senator in Ohio who served four terms from 1974 to 1999. People across social media, including notable celebrities and figures like Elon Musk and Neil deGrasse Tyson, are expressing their sadness about Glenn's passing. See some of these tweets ahead remembering an American hero.