Question

The dusk is the time, when the sun _________.
A) appears
B) disappears
C) rise
D) None of these

Answer 1

Hint: The Sun is the central star of the Solar System. It's a nearly ideal sphere of hot plasma, heated to incandescence in its centre by nuclear fusion reactions and radiating energy primarily as visible light and infrared radiation. Sun, without a doubt, the most vital source of energy for life on Earth.

Complete answer:
After the top of the Sun has reached the horizon, it is called dusk. Astronomical dusk, nautical dusk, and civil dusk occur at 18 degrees, 12 degrees, and 6 degrees below the horizon, respectively, much like the dawn.

After sunset and just before nightfall, dusk happens at the darkest point of twilight or at the very end of astronomical twilight. Predusk, during the early to intermediate stages of twilight, there may be enough light in the sky under clear conditions to read outside without artificial illumination; however, at the end of civil twilight, when the centre of the Sun's disc is 6 degrees below the local horizon, artificial illumination is needed to read outside. Usually, the word dusk refers to astronomical dusk, or the darkest part of sunset before nightfall.

That is, dusk is the interval between sunset and full darkness when the top of the setting sun only disappears under the sea-level horizon. The dusk is the time when the sun disappears.

Thus the correct answer is option ‘B’.

Note: Today, the Sun is approximately halfway through its most stable phase. It hasn't changed much in over four billion years and is expected to stay that way for another five billion. The Sun, on the other hand, will undergo drastic changes both internally and externally once hydrogen fusion in its core has stopped.