Twilight vs Dusk
Twilight and dusk are two different times of the day. The main difference between them is twilight comes twice a day and dusk just once.
Twilight
People hardly thought about twilight until the famous movie with the same name came out. Sundown and sunrise, dawn and dusk were the words used in everyday language.
“Twilight” refers to two different times. First, it refers to the time of day between sunrise and dawn, and secondly it refers to the time between dusk and sunset. It is the time when the sunlight scatters in the upper atmosphere of the Earth and illuminates the Earth’s lower atmosphere. The result is that neither the Earth is completely dark or completely lit. This time is a very favorite time with painters and photographers and also early risers who love to watch the sunrise. It is referred to as the blue hour. At this time, the sun is below the horizon of the Earth and is not directly visible. There is a distinctive light at this time of the day which is neither like night nor like day. At twilight, the upper atmosphere provides natural light from the sun directly and scatters some of it on the Earth.
Technically, twilight has three subcategories, and it is defined by the solar elevation angle. The solar elevation angle is the sun’s geometric center relative to Earth’s horizon. The three subcategories are:
Civil Twilight
Civil twilight is the brightest. At this time, the horizon can be seen clearly and without the help of artificial light. The terrestrial objects can be easily perceived. Civil twilight is again differentiated into civil dawn. This time ends at sunrise, and the sun’s geometric center is six degrees below the horizon. Civil dusk starts at sunset. It ends when the sun’s geometric center reaches six degrees below the horizon.
Nautical Twilight
Nautical twilight is when the sun’s geometric center is between 6 degrees and 12 degrees below the Earth’s horizon. It is called nautical mainly because of its use in navigation at sea. It ends when navigation at sea via the horizon is not possible anymore.
Astronomical Twilight
This period is the darkest twilight. At this time the sun’s epicenter is 12-18 degrees below the Earth’s horizon. It is called astronomical twilight because at this time, which is between evening and morning, the sky is dark enough for all kinds of astronomical observations.
Dusk
Dusk is the time of evening which starts after the evening twilight. It is considered the beginning of the evening. At dusk the sky is blue and bright. Civil dusk marks the end of the civil twilight, and the sun’s epicenter is six degrees below the Earth’s horizon. It occurs before sunset. Artificial light is required for reading outside during dusk.
Summary:
1.“Twilight” refers to the time of day between sunrise and dawn and, secondly, to the time between dusk and sunset. 2.“Dusk” refers to the time when evening starts and artificial light is required to read outside. It starts at the end of civil twilight.