Thy sun
shemesh  (sheh'-mesh)
the sun; by implication, the east; figuratively, a ray, i.e. (arch.) a notched battlement -- + east side(-ward), sun (rising), + west(-ward), window.
shall no more go down
bow'  (bo)
to go or come (in a wide variety of applications)
neither shall thy moon
yerach  (yeh'-rakh)
a lunation, i.e. month -- month, moon.
'acaph  (aw-saf')
to gather for any purpose; hence, to receive, take away, i.e. remove
itself for the LORD
Yhovah  (yeh-ho-vaw')
(the) self-Existent or Eternal; Jehovah, Jewish national name of God -- Jehovah, the Lord.
shall be thine everlasting
`owlam  (o-lawm')
concealed, i.e. the vanishing point; generally, time out of mind (past or future), i.e. (practically) eternity; frequentatively, adverbial (especially with prepositional prefix) always
'owr  (ore)
illumination or (concrete) luminary (in every sense, including lightning, happiness, etc.) -- bright, clear, + day, light (-ning), morning, sun.
and the days
yowm  (yome)
a day (as the warm hours),
of thy mourning
'ebel  (ay'-bel)
lamentation -- mourning.
shall be ended
shalam  (shaw-lam')
to be safe (in mind, body or estate); figuratively, to be (causatively, make) completed; by implication, to be friendly; by extension, to reciprocate