text:  Because the orbit of the Moon is <unk> only 5 ° from the ecliptic , the interior of this crater lies in perpetual darkness . Estimates of the area in permanent shadow were obtained from Earth @-@ based radar studies . <unk> along the rim of the crater are almost continually illuminated by sunlight , spending about 80 – 90 % of each lunar orbit exposed to the Sun . <unk> illuminated mountains have been termed peaks of eternal light and have been predicted to exist since the 1900s . 
  