The yellow dots are airplanes in the sky during a 24 hour period. Stay with the picture. You will see the light of the day moving from the east to the west, as the Earth spins on its axis.
Also you will see the aircraft flow of traffic leaving the North American continent and traveling at night to arrive in the UK in the morning. Then you will see the flow changing, leaving the UK in the morning and flying to the American continent in daylight.