Neil deGrasse Tyson @neiltyson
Mach-Talk... Your speed relative to the speed of sound in the medium you are traveling is called your Mach Number. Mach-1 is the speed of sound. Mach-2 is 2x the speed of sound, etc. At Mach-1 and higher you create a sonic boom. High Mach numbers cause more energetic booms. — PolitiTweet.org