Twilight is the period of the day when there is still light in the air after the Sun has set below the horizon. This happens because Earth's atmosphere scatters sunlight, creating the characteristic colors of twilight. On worlds without an atmosphere, such as the Moon, the sky becomes immediately dark when the Sun sets.
There are three types of twilight after sunset. The article mentions that there are three twilights, although the text was cut off before explaining them in detail.
If it were possible to observe twilight from space, it would be visible that there is no sharp boundary on Earth's surface. The shadow line over the planet, called the terminator line, extends over a fairly wide area rather than being a defined division.
