In the United States and Canada, digital clocks and computers usually show 12 a.m. right at midnight. However, people have to remember that any time is actually an instant. The "a.m." shown on clock displays means the 12-hour period after the instant of midnight. So when a clock says "12:00 a.m.", midnight has already passed and a new day has started. In other words, 11:59 p.m. shows until midnight; at the instant of midnight, it changes to 12:00. At the same time, the p.m. changes to a.m., but a.m. does not mean the instant of midnight which separates p.m. and a.m.