dusk vs solar year

dusk

noun
  • A period of time at the end of day when the sun is below the horizon but before the full onset of night, especially the darker part of twilight. 

  • A darkish colour. 

  • The condition of being dusky; duskiness 

adj
  • Tending to darkness or blackness; moderately dark or black; dusky. 

verb
  • To begin to lose light or whiteness; to grow dusk. 

  • To make dusk. 

solar year

noun
  • The time it takes the Earth to pass once around the Sun, as reckoned with respect to the seasons and not the fixed stars (for instance from vernal equinox to vernal equinox). 

  • The time it takes for any astronomical object (such as a planet, dwarf planet, small Solar System body, or comet) in direct orbit around a star (such as the Sun) to make one revolution around the star, taking into account orbital precession. 

How often have the words dusk and solar year occurred in a corpus of books? (source: Google Ngram Viewer )