SDTV and high definition television (HDTV) are the two categories of display formats for digital television (DTV) transmissions, which are becoming the standard. In North America, digital SDTV is broadcast in the same 4:3 aspect ratio as NTSC signals with widescreen content being center cut.
Command pilot Neil Armstrong 's flight marked the second time a U.S. civilian flew into space (Joseph Albert Walker became the first U.S. civilian on X-15 Flight 90). Armstrong had resigned his commission in the United States Naval Reserve in 1960.
Neil Armstrong and Edwin Aldrin spent a total of 21 hours on the Moon, two-and-a-half of them outside the landing module. After re-joining the Columbia mothership the astronauts-including Collins-left the Moon's orbit on 22 July and returned to Earth on 24 July.