The line that separates day and night is called the terminator. It is also referred to as the "grey line" and the "twilight zone." It is a fuzzy line due to our atmosphere bending sunlight. In fact, the atmosphere bends sunlight by half a degree, which is about 37 miles (60 km). It is commonly thought that while half of the Earth is covered in darkness, the other half is covered in sunlight. This is actually not true because of the bending of the sunlight results in the land covered by sunlight

OLT ( OPTICAL LINE TERMINAL )